Amarin (AMRN) 10-Q 3 Nov 21 2021 Q3 Quarterly report Financial data

Document and Entity Information

Document and Entity Information - shares	9 Months Ended
	Sep. 30, 2021	Oct. 29, 2021
Document And Entity Information [Line Items]
Document Type	10-Q
Amendment Flag	false
Document Period End Date	Sep. 30, 2021
Document Fiscal Year Focus	2021
Document Fiscal Period Focus	Q3
Trading Symbol	AMRN
Entity Registrant Name	AMARIN CORP PLC\UK
Entity Central Index Key	0000897448
Current Fiscal Year End Date	--12-31
Entity Filer Category	Large Accelerated Filer
Entity Emerging Growth Company	false
Entity Small Business	false
Entity Current Reporting Status	Yes
Entity Interactive Data Current	Yes
Entity Shell Company	false
Entity File Number	000-21392
Entity Incorporation, State or Country Code	X0
Entity Address, Address Line One	77 Sir John Rogerson’s Quay
Entity Address, Address Line Two	Block C
Entity Address, Address Line Three	Grand Canal Docklands
Entity Address, City or Town	Dublin
Entity Address, Postal Zip Code	2
Entity Address, Country	IE
City Area Code	353 (0) 1
Local Phone Number	6699 020
Document Quarterly Report	true
Document Transition Report	false
Title of each class	American Depositary Shares (ADS(s)), each ADSrepresenting the right to receive one (1) Ordinary Share ofAmarin Corporation plc
Name of each exchange on which registered	NASDAQ
Entity Tax Identification Number	00-0000000
American Depositary Shares
Document And Entity Information [Line Items]
Entity Common Stock, Shares Outstanding		395,629,060
Ordinary Shares
Document And Entity Information [Line Items]
Entity Common Stock, Shares Outstanding		196,827

Condensed Consolidated Balance

Condensed Consolidated Balance Sheets - USD ($) $ in Thousands	Sep. 30, 2021	Dec. 31, 2020
Current Assets:
Cash and cash equivalents	$ 222,875	$ 186,964
Restricted cash	3,917	3,915
Short-term investments	256,267	313,969
Accounts receivable, net	149,361	154,574
Inventory	309,268	188,864
Prepaid and other current assets	21,345	30,947
Total current assets	963,033	879,233
Property, plant and equipment, net	1,569	2,016
Long-term investments	38,802	62,469
Operating lease right-of-use asset	7,762	8,054
Other long-term assets	456	432
Intangible asset, net	24,183	13,817
TOTAL ASSETS	1,035,805	966,021
Current Liabilities:
Accounts payable	72,415	105,876
Accrued expenses and other current liabilities	289,684	198,641
Current deferred revenue	2,646	2,926
Total current liabilities	364,745	307,443
Long-Term Liabilities:
Long-term deferred revenue	14,486	15,706
Long-term operating lease liability	8,729	9,153
Other long-term liabilities	5,350	6,214
Total liabilities	393,310	338,516
Commitments and contingencies (Note 5)
Stockholders’ Equity:
Common stock, GBP 0.50 par, unlimited authorized; 402,772,229 shares issued, 395,613,406 shares outstanding as of September 30, 2021; 398,425,000 shares issued, 392,538,081 shares outstanding as of December 31, 2020	293,140	290,115
Additional paid-in capital	1,845,103	1,817,649
Treasury stock; 7,158,823 shares as of September 30, 2021; 5,886,919 shares as of December 31, 2020	(59,602)	(51,082)
Accumulated deficit	(1,436,146)	(1,429,177)
Total stockholders’ equity	642,495	627,505
TOTAL LIABILITIES AND STOCKHOLDERS’ EQUITY	$ 1,035,805	$ 966,021

Condensed Consolidated Balanc_2

Condensed Consolidated Balance Sheets (Parenthetical) - £ / shares	Sep. 30, 2021	Dec. 31, 2020
Statement of Financial Position [Abstract]
Common stock, par value	£ 0.50	£ 0.50
Common stock, shares authorized, unlimited	Unlimited	Unlimited
Common stock, issued	402,772,229	398,425,000
Common stock, outstanding	395,613,406	392,538,081
Treasury stock, shares	7,158,823	5,886,919

Condensed Consolidated Statemen

Condensed Consolidated Statements of Operations - USD ($) shares in Thousands, $ in Thousands	3 Months Ended		9 Months Ended
	Sep. 30, 2021	Sep. 30, 2020	Sep. 30, 2021	Sep. 30, 2020
Total revenue, net	$ 142,038	$ 156,499	$ 438,696	$ 446,809
Less: Cost of goods sold	30,211	33,071	90,692	96,676
Gross margin	111,827	123,428	348,004	350,133
Operating expenses:
Selling, general and administrative	102,965	120,164	315,966	346,496
Research and development	7,820	10,204	23,554	30,450
Restructuring	14,115		14,115
Total operating expenses	124,900	130,368	353,635	376,946
Operating loss	(13,073)	(6,940)	(5,631)	(26,813)
Interest income, net	163	549	919	1,908
Other (expense) income, net	(57)	33	(390)	50
Loss from operations before taxes	(12,967)	(6,358)	(5,102)	(24,855)
Income tax (provision) benefit	(184)	(430)	(1,867)	1,929
Net loss	$ (13,151)	$ (6,788)	$ (6,969)	$ (22,926)
Loss per share:
Basic	$ (0.03)	$ (0.02)	$ (0.02)	$ (0.06)
Diluted	$ (0.03)	$ (0.02)	$ (0.02)	$ (0.06)
Weighted average shares:
Basic	396,618	389,699	395,681	378,770
Diluted	396,618	389,699	395,681	378,770
Product Revenue, Net
Total revenue, net	$ 141,442	$ 155,190	$ 436,598	$ 441,118
Licensing and Royalty Revenue
Total revenue, net	$ 596	$ 1,309	$ 2,098	$ 5,691

Condensed Consolidated Statem_2

Condensed Consolidated Statement of Changes in Stockholders' Equity - USD ($) $ in Thousands	Total	Preferred Shares	Common Shares	Treasury Stock	Additional Paid-in Capital	Accumulated Deficit
Balance at Dec. 31, 2019	$ 608,263	$ 21,850	$ 269,173	$ (35,900)	$ 1,764,317	$ (1,411,177)
Balance (in shares) at Dec. 31, 2019		289,317,460	365,014,893
Balance, Treasury Shares (in shares) at Dec. 31, 2019				(4,910,992)
Exercise of stock options	1,306		$ 269		1,037
Exercise of stock options (in shares)			412,465
Vesting of restricted stock units	(13,831)		$ 1,274	$ (13,831)	(1,274)
Vesting of restricted stock units (in shares)			1,951,448	(759,832)
Stock-based compensation	10,591				10,591
Income (Loss) for the period	(20,553)					(20,553)
Balance at Mar. 31, 2020	585,776	$ 21,850	$ 270,716	$ (49,731)	1,774,671	(1,431,730)
Balance (in shares) at Mar. 31, 2020		289,317,460	367,378,806
Balance, Treasury Shares (in shares) at Mar. 31, 2020				(5,670,824)
Balance at Dec. 31, 2019	$ 608,263	$ 21,850	$ 269,173	$ (35,900)	1,764,317	(1,411,177)
Balance (in shares) at Dec. 31, 2019		289,317,460	365,014,893
Balance, Treasury Shares (in shares) at Dec. 31, 2019				(4,910,992)
Exercise of stock options (in shares)	642,756
Income (Loss) for the period	$ (22,926)
Balance at Sep. 30, 2020	607,257	$ 5,434	$ 287,585	$ (50,728)	1,799,069	(1,434,103)
Balance (in shares) at Sep. 30, 2020		23,850,780	394,642,079
Balance, Treasury Shares (in shares) at Sep. 30, 2020				(5,813,385)
Balance at Dec. 31, 2019	608,263	$ 21,850	$ 269,173	$ (35,900)	1,764,317	(1,411,177)
Balance (in shares) at Dec. 31, 2019		289,317,460	365,014,893
Balance, Treasury Shares (in shares) at Dec. 31, 2019				(4,910,992)
Balance at Dec. 31, 2020	$ 627,505		$ 290,115	$ (51,082)	1,817,649	(1,429,177)
Balance (in shares) at Dec. 31, 2020			398,425,000
Balance, Treasury Shares (in shares) at Dec. 31, 2020	5,886,919			(5,886,919)
Balance at Mar. 31, 2020	$ 585,776	$ 21,850	$ 270,716	$ (49,731)	1,774,671	(1,431,730)
Balance (in shares) at Mar. 31, 2020		289,317,460	367,378,806
Balance, Treasury Shares (in shares) at Mar. 31, 2020				(5,670,824)
Issuance of common stock under employee stock purchase plan	848		$ 76		772
Issuance of common stock under employee stock purchase plan (in shares)			123,608
Conversion of Series A Convertible Preferred Stock, net	(238)	$ (14,684)	$ 14,684		(238)
Conversion of Series A Convertible Preferred Stock, net (in shares)		(237,713,680)	23,771,368
Exercise of stock options	352		$ 92		260
Exercise of stock options (in shares)			148,290
Vesting of restricted stock units	(521)		$ 104	$ (521)	(104)
Vesting of restricted stock units (in shares)			167,240	(70,971)
Stock-based compensation	12,131				12,131
Income (Loss) for the period	4,415					4,415
Balance at Jun. 30, 2020	602,763	$ 7,166	$ 285,672	$ (50,252)	1,787,492	(1,427,315)
Balance (in shares) at Jun. 30, 2020		51,603,780	391,589,312
Balance, Treasury Shares (in shares) at Jun. 30, 2020				(5,741,795)
Conversion of Series A Convertible Preferred Stock, net	(28)	$ (1,732)	$ 1,732		(28)
Conversion of Series A Convertible Preferred Stock, net (in shares)		(27,753,000)	2,775,300
Exercise of stock options	203		$ 53		150
Exercise of stock options (in shares)			82,001
Vesting of restricted stock units	(476)		$ 128	$ (476)	(128)
Vesting of restricted stock units (in shares)			195,466	(71,590)
Stock-based compensation	11,583				11,583
Income (Loss) for the period	(6,788)					(6,788)
Balance at Sep. 30, 2020	607,257	$ 5,434	$ 287,585	$ (50,728)	1,799,069	(1,434,103)
Balance (in shares) at Sep. 30, 2020		23,850,780	394,642,079
Balance, Treasury Shares (in shares) at Sep. 30, 2020				(5,813,385)
Balance at Dec. 31, 2020	$ 627,505		$ 290,115	$ (51,082)	1,817,649	(1,429,177)
Balance (in shares) at Dec. 31, 2020			398,425,000
Balance, Treasury Shares (in shares) at Dec. 31, 2020	5,886,919			(5,886,919)
Exercise of stock options	$ 2,059		$ 536		1,523
Exercise of stock options (in shares)			783,320
Vesting of restricted stock units	(7,252)		$ 1,709	$ (7,252)	(1,709)
Vesting of restricted stock units (in shares)			2,447,405	(1,003,965)
Stock-based compensation	13,925				13,925
Income (Loss) for the period	(1,626)					(1,626)
Balance at Mar. 31, 2021	634,611		$ 292,360	$ (58,334)	1,831,388	(1,430,803)
Balance (in shares) at Mar. 31, 2021			401,655,725
Balance, Treasury Shares (in shares) at Mar. 31, 2021				(6,890,884)
Balance at Dec. 31, 2020	$ 627,505		$ 290,115	$ (51,082)	1,817,649	(1,429,177)
Balance (in shares) at Dec. 31, 2020			398,425,000
Balance, Treasury Shares (in shares) at Dec. 31, 2020	5,886,919			(5,886,919)
Exercise of stock options (in shares)	994,921
Income (Loss) for the period	$ (6,969)
Balance at Sep. 30, 2021	$ 642,495		$ 293,140	$ (59,602)	1,845,103	(1,436,146)
Balance (in shares) at Sep. 30, 2021			402,772,229
Balance, Treasury Shares (in shares) at Sep. 30, 2021	7,158,823			(7,158,823)
Balance at Mar. 31, 2021	$ 634,611		$ 292,360	$ (58,334)	1,831,388	(1,430,803)
Balance (in shares) at Mar. 31, 2021			401,655,725
Balance, Treasury Shares (in shares) at Mar. 31, 2021				(6,890,884)
Issuance of common stock under employee stock purchase plan	1,028		$ 161		867
Issuance of common stock under employee stock purchase plan (in shares)			226,402
Exercise of stock options	75		$ 19		56
Exercise of stock options (in shares)			27,139
Vesting of restricted stock units	(677)		$ 242	$ (677)	(242)
Vesting of restricted stock units (in shares)			346,010	(142,204)
Stock-based compensation	2,479				2,479
Income (Loss) for the period	7,808					7,808
Balance at Jun. 30, 2021	645,324		$ 292,782	$ (59,011)	1,834,548	(1,422,995)
Balance (in shares) at Jun. 30, 2021			402,255,276
Balance, Treasury Shares (in shares) at Jun. 30, 2021				(7,033,088)
Exercise of stock options	481		$ 128		353
Exercise of stock options (in shares)			184,462
Vesting of restricted stock units	(591)		$ 230	$ (591)	(230)
Vesting of restricted stock units (in shares)			332,491	(125,735)
Stock-based compensation	10,432				10,432
Income (Loss) for the period	(13,151)					(13,151)
Balance at Sep. 30, 2021	$ 642,495		$ 293,140	$ (59,602)	$ 1,845,103	$ (1,436,146)
Balance (in shares) at Sep. 30, 2021			402,772,229
Balance, Treasury Shares (in shares) at Sep. 30, 2021	7,158,823			(7,158,823)

Condensed Consolidated Statem_3

Condensed Consolidated Statements of Cash Flows - USD ($) $ in Thousands	9 Months Ended
	Sep. 30, 2021	Sep. 30, 2020
CASH FLOWS FROM OPERATING ACTIVITIES:
Net loss	$ (6,969)	$ (22,926)
Adjustments to reconcile loss to net cash (used in) provided by operating activities:
Depreciation and amortization	443	446
Amortization of investments	1,564	771
Stock-based compensation	26,836	34,305
Amortization of debt discount and debt issuance costs		601
Amortization of intangible asset	1,633	1,081
Changes in assets and liabilities:
Accounts receivable, net	5,213	(30,862)
Inventory	(120,404)	(71,762)
Prepaid and other current assets	9,601	(13,023)
Other long-term assets	(24)
Interest receivable	723	(1,732)
Accrued interest payable		(348)
Deferred revenue	(1,500)	(1,941)
Accounts payable and other current liabilities	45,582	121,240
Other long-term liabilities	(995)	727
Net cash (used in) provided by operating activities	(38,297)	16,577
CASH FLOWS FROM INVESTING ACTIVITIES:
Sale and maturities of securities	312,150	186,714
Purchases of securities	(233,067)	(587,111)
Disposal (purchase) of furniture, fixtures and equipment	4	(252)
Net cash provided by (used in) investing activities	79,087	(400,649)
CASH FLOWS FROM FINANCING ACTIVITIES:
Proceeds from issuance of common stock, net of transaction costs	1,028	848
Proceeds from exercise of stock options, net of transaction costs	2,615	1,861
Payment of transaction costs for conversion of preferred stock		(266)
Payment on debt from royalty-bearing instrument		(40,916)
Taxes paid related to stock-based awards	(8,520)	(14,828)
Net cash used in financing activities	(4,877)	(53,301)
NET INCREASE (DECREASE) IN CASH AND CASH EQUIVALENTS AND RESTRICTED CASH	35,913	(437,373)
CASH AND CASH EQUIVALENTS AND RESTRICTED CASH, BEGINNING OF PERIOD	190,879	648,495
CASH AND CASH EQUIVALENTS AND RESTRICTED CASH, END OF PERIOD	226,792	211,122
Cash Received Paid During Period For [Abstract]
Interest		(1,882)
Income taxes	3,670	$ (197)
Supplemental disclosure of non-cash transactions:
Laxdale Milestone	$ 12,000

Nature of Business and Basis of

Nature of Business and Basis of Presentation	9 Months Ended
	Sep. 30, 2021
Accounting Policies [Abstract]
Nature of Business and Basis of Presentation	(1) Nature of Business and Basis of Presentation Nature of Business Amarin Corporation plc, or Amarin, or the Company, is a pharmaceutical company focused on the commercialization and development of therapeutics to improve cardiovascular health and reduce cardiovascular risk. Most of the Company’s historical revenue and sales, marketing and administrative activities and costs have been associated with commercial operations in the United States, or U.S. In 2021 the Company began to increase pre-launch commercial activities throughout Europe. As of September 1, 2021, product was made available in Germany and as of October 1, 2021 was included in the country's electronic prescribing system. The Company’s operations outside of the U.S. and Europe are in early stages of development with reliance on third-party commercial partners in select geographies, including China where regulatory approval for the Company’s lead product is being actively sought. The Company’s lead product, VASCEPA ® (icosapent ethyl), was first approved by the U.S. Food and Drug Administration, or U.S. FDA, in July 2012 for use as an adjunct to diet to reduce triglyceride, or TG, levels in adult patients with severe ( > 500 mg/dL) hypertriglyceridemia. In January 2013, the Company launched 1-gram size VASCEPA in the U.S. and in October 2016, introduced a smaller 0.5-gram capsule size. On December 13, 2019, the U.S. FDA approved an indication and label expansion for VASCEPA based on the results of the Company’s long-term cardiovascular outcomes trial, REDUCE-IT ® , or Reduction of Cardiovascular Events with EPA – Intervention Trial. VASCEPA is approved by the U.S. FDA as an adjunct to maximally tolerated statin therapy for reducing persistent cardiovascular risk in select high risk patients. VASCEPA is also available for sale by prescription only in Canada, Lebanon and the United Arab Emirates through collaborations and is also in development in other jurisdictions. On March 30, 2020, following conclusion of a trial in late January 2020, the U.S. District Court for the District of Nevada, or the Nevada Court, issued a ruling in favor of two generic drug companies, Dr. Reddy’s Laboratories, Inc., or Dr. Reddy’s, and Hikma Pharmaceuticals USA Inc., or Hikma, and certain of their affiliates, or, collectively, the Defendants, that declared as invalid several of the Company's patents covering the first FDA-approved use of its drug, for use to reduce severely high triglyceride levels, which is known as the MARINE indication. The Company sought appeals of the Nevada Court judgment up to the United States Supreme Court, but the Company was unsuccessful. Most recently, on June 18, 2021, the Company was notified that its petition for writ of certiorari to the United States Supreme Court was denied. On May 22, 2020, Hikma received U.S. FDA approval to market its generic version of VASCEPA for the MARINE indication of VASCEPA. In November 2020, Hikma launched their generic version of VASCEPA on a limited scale. On August 10, 2020, Dr. Reddy's received U.S. FDA approval to market its generic version for the MARINE indication of VASCEPA. In June 2021, Dr. Reddy’s launched its generic version of VASCEPA with labeling that is substantially similar to labeling of the Hikma generic product. On September 11, 2020, Teva Pharmaceuticals USA, Inc’s., or Teva’s, abbreviated new drug application, or ANDA, was approved by the U.S. FDA and on June 30, 2021, Apotex, Inc.'s, or Apotex's, ANDA was approved by the U.S. FDA. In August 2020, the Company announced plans to launch icosapent ethyl under the brand name VAZKEPA, hereinafter along with the U.S. brand name VASCEPA, collectively referred to as VASCEPA, in major markets in Europe through the Company’s new European sales and marketing teams. On January 29, 2021, the Committee for Medicinal Products for Human Use, or CHMP, of the European Medicines Agency, or EMA, adopted a positive opinion, recommending that a marketing authorization be granted to icosapent ethyl in the European Union, or EU, for the reduction of risk of cardiovascular events in patients at high cardiovascular risk. On March 26, 2021, the European Commission, or EC, approved the marketing authorization application for VAZKEPA in the EU to reduce the risk of cardiovascular events in high-risk, statin-treated adult patients who have elevated triglycerides ( > 150 mg/dL) and either established cardiovascular disease or diabetes and at least one additional cardiovascular risk event. On September 13, 2021, the Company launched VAZKEPA in Germany, representing the Company's first European launch of VAZKEPA. On April 22, 2021, the Company announced that the Medicines and Healthcare Products Regulatory Agency, or MHRA, approved VAZKEPA in England, Scotland and Wales to reduce cardiovascular risk through MHRA’s new ‘reliance’ route following the end of the BREXIT transition period. Collectively CHMP, EMA, EC and MHRA are referred to herein as the European Regulatory Authorities. In November 2020, the Company announced topline results from the Phase 3 clinical trial of VASCEPA conducted by the Company’s partner in China. On February 9, 2021, the Company announced that regulatory review processes for approval of VASCEPA in Mainland China and Hong Kong have commenced. The Chinese National Medical Products Administration, or NMPA, has accepted for review the new drug application for VASCEPA based on the results from the Phase 3 clinical trial and the results from the Company’s prior studies of VASCEPA. The Hong Kong Department of Health is evaluating VASCEPA based on current approvals in the United States and Canada. The Company currently has strategic collaborations to develop and commercialize VASCEPA in select territories outside the United States. Amarin is responsible for supplying VASCEPA to all markets in which the product is sold, including the United States and Germany, as well as, in Canada, Lebanon and the United Arab Emirates where the drug is promoted and sold via collaboration with third-party companies that compensate Amarin for such supply. Amarin is not responsible for providing any generic company with drug product. The Company operates in one business segment. Basis of Presentation The condensed consolidated financial statements included herein have been prepared by the Company in accordance with accounting principles generally accepted in the United States and pursuant to the rules and regulations of the Securities and Exchange Commission, or the SEC. Certain information in the footnote disclosures of the financial statements has been condensed or omitted where it substantially duplicates information provided in the Company’s latest audited consolidated financial statements, in accordance with the rules and regulations of the SEC. These condensed consolidated financial statements should be read in conjunction with the Company’s audited consolidated financial statements and notes included in its Annual Report on Form 10-K for the fiscal year ended, or the Form 10-K, filed with the SEC. The balance sheet amounts in this report were derived from the Company’s audited consolidated financial statements included in the Form 10-K. The condensed consolidated financial statements reflect all adjustments of a normal and recurring nature that, in the opinion of management, are necessary to present fairly the Company’s financial position, results of operations and cash flows for the periods indicated. The preparation of the Company’s condensed consolidated financial statements in conformity with U.S. Generally Accepted Accounting Principles, or GAAP, requires management to make estimates and assumptions that affect the reported amounts of assets and liabilities, disclosure of contingent assets and liabilities at the date of the financial statements, and the reported amounts of revenues and expenses during the reporting period. The results of operations for the three and nine months ended September 30, 2021 and 2020 are not necessarily indicative of the results for any future period. Certain numbers presented throughout this document may not add precisely to the totals provided due to rounding. Absolute and percentage changes are calculated using the underlying amounts in thousands. The condensed consolidated financial statements include the accounts of the Company and its wholly-owned subsidiaries. All intercompany accounts and transactions have been eliminated in consolidation. The accompanying condensed consolidated financial statements of the Company and subsidiaries have been prepared on a basis which assumes that the Company will continue as a going concern, which contemplates the realization of assets and the satisfaction of liabilities and commitments in the normal course of business, as well as the current global pandemic, COVID-19. At September 30, 2021, the Company had Total assets of $ 1,035.8 million, of which $ 517.9 million consisted of cash and liquid short-term and long-term investments. More specifically, the Company had Current assets of $ 963.0 million, including Cash and cash equivalents of $ 222.9 million, Short-term investments of $ 256.3 million, Accounts receivable, net, of $ 149.4 million and Inventory of $ 309.3 million. In addition, as of September 30, 2021, the Company had Long-term investments of $ 38.8 million. As of September 30, 2021 , the Company had no debt outstanding.

Significant Accounting Policies

Significant Accounting Policies	9 Months Ended
	Sep. 30, 2021
Accounting Policies [Abstract]
Significant Accounting Policies	(2) Significant Accounting Policies Revenue Recognition In accordance with Accounting Standards Codification, or ASC, Topic 606, Revenue from Contracts with Customers , or Topic 606, the Company recognizes revenue when its customer obtains control of promised goods or services, in an amount that reflects the consideration which the entity expects to receive in exchange for those goods or services. To determine revenue recognition for arrangements that an entity determines are within the scope of Topic 606, the entity performs the following five steps: (i) identify the contract(s) with a customer; (ii) identify the performance obligations in the contract; (iii) determine the transaction price; (iv) allocate the transaction price to the performance obligations in the contract; and (v) recognize revenue when (or as) the entity satisfies a performance obligation. The Company only applies the five-step model to contracts when it is probable that the entity will collect the consideration it is entitled to in exchange for the goods or services it transfers to the customer. At contract inception, once the contract is determined to be within the scope of Topic 606, the Company assesses the goods or services promised within each contract and determines those that are performance obligations and assesses whether each promised good or service is distinct. The Company then recognizes as revenue the amount of the transaction price that is allocated to the respective performance obligation when (or as) the performance obligation is satisfied. For a complete discussion of accounting for net product revenue and licensing revenue, see Note 8—Revenue Recognition. Cash and Cash Equivalents and Restricted Cash Cash and cash equivalents consist of cash, deposits with banks and short-term highly liquid money market instruments with remaining maturities at the date of purchase of 90 days or less. Restricted cash represents cash and cash equivalents pledged to guarantee repayment of certain expenses which may be incurred for business travel under corporate credit cards held by employees. Accounts Receivable, net Accounts receivable, net, comprised of trade receivables, are generally due within 30 days and are stated at amounts due from customers. The Company recognizes an allowance for losses on accounts receivable in an amount equal to the estimated probable losses net of any recoveries. The allowance is based primarily on assessment of specific identifiable customer accounts considered at risk or uncollectible, as well as an analysis of current receivables aging and expected future write-offs. The expense associated with the allowance for doubtful accounts is recognized as Selling, general, and administrative expense. The Company has not historically experienced any significant credit losses. All customer accounts are actively managed and no losses in excess of amounts reserved are currently expected; however, the Company is monitoring the potential negative impact of COVID-19 on the Company’s customers’ ability to meet their financial obligations. The following table summarizes the impact of accounts receivable reserves on the gross trade accounts receivable balances as of September 30, 2021 and December 31, 2020: In thousands September 30, 2021 December 31, 2020 Gross trade accounts receivable $ 229,138 $ 203,875 Trade allowances ( 64,857 ) ( 36,242 ) Chargebacks ( 13,975 ) ( 12,114 ) Allowance for doubtful accounts ( 945 ) ( 945 ) Accounts receivable, net $ 149,361 $ 154,574 Inventory The Company states inventories at the lower of cost or net realizable value. Cost is determined based on actual cost using the average cost method. Net realizable value is the estimated selling price in the ordinary course of business, less reasonably predictable costs of completion, disposal, and transportation. An allowance is established when management determines that certain inventories may not be saleable. If inventory cost exceeds expected net realizable value due to obsolescence, damage or quantities in excess of expected demand, changes in price levels or other causes, the Company will reduce the carrying value of such inventory to net realizable value and recognize the difference as a component of cost of goods sold in the period in which it occurs. The Company capitalizes inventory purchases of saleable product from approved suppliers while inventory purchases from suppliers prior to regulatory approval are included as a component of research and development expense. The Company expenses inventory identified for use as marketing samples when they are packaged. The average cost reflects the actual purchase price of VASCEPA active pharmaceutical ingredient, or API. Income Taxes Deferred tax assets and liabilities are recognized for the future tax consequences of differences between the carrying amounts and tax bases of assets and liabilities and operating loss carryforwards and other tax attributes using enacted rates expected to be in effect when those differences reverse. Valuation allowances are provided against deferred tax assets that are not more likely than not to be realized. Deferred tax assets and liabilities are classified as non-current in the condensed consolidated balance sheet. The Company provides reserves for potential payments of tax to various tax authorities and does not recognize tax benefits related to uncertain tax positions and other issues. Tax benefits for uncertain tax positions are based on a determination of whether a tax benefit taken by the Company in its tax filings or positions is more likely than not to be realized, assuming that the matter in question will be decided based on its technical merits. The Company’s policy is to record interest and penalties in the provision for income taxes, as applicable. The Company regularly assesses its ability to realize deferred tax assets. Changes in historical earnings performance, future earnings projections, and changes in tax laws, among other factors, may cause the Company to adjust its valuation allowance on deferred tax assets, which would impact the Company’s income tax expense in the period in which it is determined that these factors have changed. Excess tax benefits and deficiencies that arise upon vesting or exercise of share-based payments are recognized as an income tax benefit and expense, respectively, in the condensed consolidated statement of operations. Excess income tax benefits are classified as cash flows from operating activities and cash paid to taxing authorities arising from the withholding of shares from employees are classified as cash flows from financing activities. The Company’s and its subsidiaries’ income tax returns are periodically examined by various tax authorities, including the Internal Revenue Service, or IRS, and states. The Company is currently under audit by the IRS for the Company’s 2018 U.S. income tax return and by the New Jersey Department of Treasury for the years 2012 to 2015 and the New York State Department of Taxation and Finance for the years 2017 and 2018 . Although the outcome of tax audits is always uncertain and could result in significant cash tax payments, the Company does not believe the outcome of these audits will have a material adverse effect on its consolidated financial position or results of operations. Loss per Share Basic net loss per share is determined by dividing net loss by the weighted average shares of common stock outstanding during the period. Diluted net loss per share is determined by dividing net loss by diluted weighted average shares outstanding. Diluted weighted average shares reflects the dilutive effect, if any, of potentially dilutive common shares, such as common stock options calculated using the treasury stock method and preferred stock using the “if-converted” method. In periods with reported net operating losses, all common stock options and preferred stock outstanding are deemed anti-dilutive such that basic and diluted net loss per share are equal. The Company’s preferred stock, of which none is outstanding as of September 30, 2021 and December 31, 2020, was entitled to receive dividends on an as-if-converted basis in the same form as dividends actually paid on common shares. Accordingly, the preferred stock was considered a participating security and the Company was required to apply the two-class method to consider the impact of the preferred stock on the calculation of basic and diluted earnings per share. The Company is in a net loss position for all of the periods presented and is therefore not required to present the two-class method. The calculation of net loss and the number of shares used to compute basic and diluted net loss per share for the three and nine months ended September 30, 2021 and 2020 are as follows: For the Three Months Ended September 30, For the Nine Months Ended September 30, In thousands 2021 2020 2021 2020 Net loss—basic and diluted $ ( 13,151 ) $ ( 6,788 ) $ ( 6,969 ) $ ( 22,926 ) Weighted average shares outstanding—basic and diluted 396,618 389,699 395,681 378,770 Net loss per share—basic and diluted $ ( 0.03 ) $ ( 0.02 ) $ ( 0.02 ) $ ( 0.06 ) For the three and nine months ended September 30, 2021 and 2020, the following potentially dilutive securities were not included in the computation of net loss per share because the effect would be anti-dilutive or because performance criteria were not yet met for awards contingent upon such measures: For the Three Months Ended September 30, For the Nine Months Ended September 30, In thousands 2021 2020 2021 2020 Stock options 19,146 17,479 19,146 17,479 Restricted stock and restricted stock units 10,307 7,727 10,307 7,727 Preferred stock (if converted) — 2,385 — 2,385 Stock options are anti-dilutive during periods of net earnings when the exercise price of the stock options exceeds the market price of the underlying shares on the last day of the reporting period. Restricted stock and restricted stock units are anti-dilutive during periods of net earnings when underlying performance-based vesting requirements were not achieved as of the last day of the reporting period. Concentration of Credit Risk Financial instruments that potentially subject the Company to credit risk consist primarily of cash and cash equivalents, short-term and long-term investments, and accounts receivable. The Company maintains substantially all of its cash and cash equivalents and short-term and long-term investments, in financial institutions believed to be of high-credit quality. A significant portion of the Company’s sales are to wholesalers in the pharmaceutical industry. The Company monitors the creditworthiness of customers to whom it grants credit terms and has not experienced any credit losses. The Company does not require collateral or any other security to support credit sales. Three customers individually accounted for 10% or more of the Company’s gross product sales, Customers A, B, and C accounted for 27 % , 37 % , and 28 % , respectively, of gross product sales for the nine months ended September 30, 2021, and represented 34 % , 37 % , and 21 % , respectively, of the gross accounts receivable balance as of September 30, 2021. Customers A, B, and C accounted for 25 % , 37 % , and 30 % , respectively, of gross product sales for the nine months ended September 30, 2020 and represented 37 % , 32 % , and 25 % , respectively, of the gross accounts receivable balance as of September 30, 2020 . The Company has not experienced any significant write-offs of its accounts receivable. All customer accounts are actively managed and no losses in excess of amounts reserved are currently expected; however, the Company is monitoring the potential negative impact of COVID-19 on the Company’s customers’ ability to meet their financial obligations. Concentration of Suppliers The Company has contractual freedom to source the API for VASCEPA and to procure other services supporting its supply chain and has entered into supply agreements with multiple suppliers. The Company’s supply of product for commercial sale and clinical trials is dependent upon relationships with third-party manufacturers and suppliers. The Company cannot provide assurance that its efforts to procure uninterrupted supply of VASCEPA to meet market demand will continue to be successful or that it will be able to renew current supply agreements on favorable terms or at all. Significant alteration to or disruption or termination of the Company’s current supply chain, including as a result of COVID-19, or the Company’s failure to enter into new and similar agreements in a timely fashion, if needed, could have a material adverse effect on its business, condition (financial and other), prospects or results of operations. The Company currently has manufacturing agreements with multiple independent API manufacturers and several independent API encapsulators and packagers for VASCEPA manufacturing. Each of these API manufacturers, encapsulators and packagers is U.S. FDA-approved and certain of these API manufacturers, encapsulators and packagers are also approved for the European Regulatory Authorities for the VAZKEPA manufacturing in Europe, with plans to expand such qualification in Europe to others of these suppliers. These suppliers are also used by the Company to source supply to meet the clinical trial and commercial demands of its partners in other countries. Each of these companies has qualified and validated its manufacturing processes. There can be no guarantee that these or other suppliers with which the Company may contract in the future to manufacture VASCEPA or VASCEPA API will remain qualified to do so to its specifications or that these and any future suppliers will have the manufacturing capacity to meet potential global demand for VASCEPA. Fair Value of Financial Instruments The Company provides disclosure of financial assets and financial liabilities that are carried at fair value based on the price that would be received upon sale of an asset or paid to transfer a liability in an orderly transaction between market participants at the measurement date. Fair value measurements may be classified based on the amount of subjectivity associated with the inputs to fair valuation of these assets and liabilities using the following three levels: Level 1—Inputs are unadjusted quoted prices in active markets for identical assets or liabilities that the Company has the ability to access at the measurement date. Level 2—Inputs include quoted prices for similar assets and liabilities in active markets, quoted prices for identical or similar assets or liabilities in markets that are not active, inputs other than quoted prices that are observable for the asset or liability (i.e., interest rates, yield curves, etc.) and inputs that are derived principally from or corroborated by observable market data by correlation or other means (market corroborated inputs). Level 3—Unobservable inputs that reflect the Company’s estimates of the assumptions that market participants would use in pricing the asset or liability. The Company develops these inputs based on the best information available, including its own data. The following tables present information about the estimated fair value of the Company’s assets and liabilities as of September 30, 2021 and December 31, 2020 and indicate the fair value hierarchy of the valuation techniques the Company utilized to determine such fair value: September 30, 2021 In thousands Total Level 1 Level 2 Level 3 Asset: Money Market Fund $ 116,456 $ 116,456 $ — $ — U.S. Treasury Shares 22,214 22,214 — — Corporate Bonds 95,771 — 95,771 — Commercial Paper 126,832 — 126,832 — Agency Securities 6,748 — 6,748 — Repo Securities 9,000 — 9,000 — Asset Backed Securities 9,895 — 9,895 — Certificate of Deposit 21,575 — 21,575 — Non-US Government 11,523 — 11,523 — Total $ 420,014 $ 138,670 $ 281,344 $ — December 31, 2020 In thousands Total Level 1 Level 2 Level 3 Asset: Money Market Fund $ 88,266 $ 88,266 $ — $ — U.S. Treasury Shares 48,356 48,356 — — Corporate Bonds 179,864 — 179,864 — Commercial Paper 106,650 — 106,650 — Agency Securities 20,782 — 20,782 — Repo Securities 10,000 — 10,000 — Asset Backed Securities 8,599 — 8,599 — Certificate of Deposit 6,125 — 6,125 — Non-US Government 5,240 — 5,240 — Total $ 473,882 $ 136,622 $ 337,260 $ — The carrying amount of the Company’s cash and cash equivalents approximates fair value because of their short-term nature. The cash and cash equivalents consist of cash, deposits with banks and short-term highly liquid money market instruments with remaining maturities at the date of the purchase of 90 days or less. The Company’s held-to-maturity investments are stated at amortized cost, which approximates fair value. The Company does not intend to sell these investment securities and the contractual maturities are not greater than 24 months . Those with maturities greater than 90 days and less than 12 months are included in short-term investments on its condensed consolidated balance sheet. Those with remaining maturities in excess of 12 months are included in long-term investments on its condensed consolidated balance sheet. Unrealized gains or losses on held-to-maturity securities are not recognized until maturity, except other-than-temporary unrealized losses which are recognized in earnings in the period incurred. The Company evaluates securities with unrealized losses to determine whether such losses are other than temporary. The unrealized gain for the nine months ended September 30, 2021 and 2020 was $ 0.1 million and $ 0.9 million, respectively. Interest on investments is reported in interest income. Segment and Geographical Information Operating segments are defined as components of an enterprise about which separate financial information is available that is evaluated on a regular basis by the chief operating decision-maker, or decision-making group, in deciding how to allocate resources to an individual segment and in assessing performance of the segment. The Company currently operates in one business segment, which is the development and commercialization of VASCEPA. A single management team that reports to the Company’s chief decision-maker, who is the Chief Executive Officer, comprehensively manages the business. Accordingly, the Company does not have separately reportable segments. Restructuring On September 22, 2021, the Company announced a new Go-to-Market strategy for VASCEPA, or the Plan, which aims to expand healthcare professional engagement through a new omnichannel platform, enhance managed care access and optimize VASCEPA prescriptions for cardiovascular risk reduction. As part of the process, the Company reduced its field force to approximately 300 sales representatives and completed this reduction during the three months ended September 30, 2021. The Company estimates that it will incur approximately $ 14.1 million in charges related to the reduction in force, substantially all of which are cash expenditures for one-time termination benefits and associated costs. During the three and nine months ended September 30, 2021 the Company recognized approximately $ 14.1 million within Restructuring expense in the condensed consolidated statements of operations. The following table shows the change in restructuring liability, associated with the Plan, which is included within accrued expenses and other current liabilities: In thousands Restructuring Liability Balance at December 31, 2020 $ — Costs incurred 14,115 Payments — Other (1) ( 306 ) Balance at September 30, 2021 $ 13,809 (1) - Represents the acceleration of expense associated with the vesting of certain equity awards. Recent Accounting Pronouncements From time to time, new accounting pronouncements are issued by the Financial Accounting Standards Board, or FASB, and are early adopted by the Company or adopted as of the specified effective date. In December 2019, the FASB issued ASU No. 2019-12 , Income Taxes (Topic 740), Simplifying the Accounting for Income Taxes, which simplifies the accounting for income taxes by eliminating certain exceptions to the guidance in ASC 740 related to the approach for intraperiod tax allocation, the methodology for calculating income taxes in an interim period, the recognition of deferred tax liabilities for outside basis differences, among other simplifications. The Company adopted this standard effective January 1, 2021 , which did not have an impact on the Company’s condensed consolidated financial statements. The Company believes that the impact of other recently issued but not yet adopted accounting pronouncements will not have a material impact on the Company’s condensed consolidated financial position, results of operations, and cash flows, or do not apply to the Company’s operations.

Intangible Asset

Intangible Asset	9 Months Ended
	Sep. 30, 2021
Goodwill and Intangible Assets Disclosure [Abstract]
Intangible Asset	(3) Intangible Asset Intangible asset consists of milestone payments to the former shareholders of Laxdale related to the 2004 acquisition of the rights to VASCEPA, which is the result of VASCEPA receiving marketing approval in the U.S. for the first indication in 2012, the expanded label in 2019 and marketing approval in Europe in 2021. Upon approval of the marketing authorization application for VAZKEPA in March 2021, a milestone for £ 7.5 million was achieved, which resulted in the Intangible asset increasing by $ 12.0 million. Refer to Note 5 – Commitments and Contingencies for further details. In accordance with ASC 350, the Company evaluates the remaining useful life of the intangible asset at each reporting period to determine if any events or circumstances warrant a revision to the remaining period of amortization. As of September 30, 2021, the intangible asset has an estimated weighted-average remaining life of 9.5 years. The carrying value as of September 30, 2021 and December 31, 2020 is as follows: In thousands September 30, 2021 December 31, 2020 Technology rights $ 32,081 $ 20,081 Accumulated amortization ( 7,898 ) ( 6,264 ) Intangible asset, net $ 24,183 $ 13,817

Inventory

Inventory	9 Months Ended
	Sep. 30, 2021
Inventory Disclosure [Abstract]
Inventory	(4) Inventory The Company capitalizes its purchases of saleable inventory of VASCEPA from suppliers that have been qualified by the U.S. FDA. Inventories as of September 30, 2021 and December 31, 2020 consist of the following: In thousands September 30, 2021 December 31, 2020 Raw materials $ 71,838 $ 50,657 Work in process 39,521 30,388 Finished goods 197,909 107,819 Total inventory $ 309,268 $ 188,864

Commitments and Contingencies

Commitments and Contingencies	9 Months Ended
	Sep. 30, 2021
Commitments and Contingencies Disclosure [Abstract]
Commitments and Contingencies	(5) Commitments and Contingencies Litigation – U.S. ANDAs On March 30, 2020, the United States District Court for the District of Nevada, or the Nevada Court, ruled in favor of two generics companies, Hikma and Dr. Reddy’s, in Amarin’s patent litigation related to its ANDAs that sought U.S. FDA approval for sale of generic versions of VASCEPA for the original indication of VASCEPA as an adjunct to diet to reduce TG levels in adult patients with severe (>500 mg/dL) hypertriglyceridemia. On September 3, 2020, the U.S. Court of Appeals for the Federal Circuit, or the Federal Circuit, upheld the March ruling by the Nevada Court in favor of the two generics companies. On October 2, 2020, the Company filed a combined petition for panel rehearing or rehearing en banc. On November 4, 2020, the Company’s rehearing and en banc petitions were denied. On February 11, 2021, Amarin filed a petition for a writ of certiorari with the United States Supreme Court to ask the Court to hear the Company’s appeal in this litigation, which was denied on June 18, 2021. On May 22, 2020 and August 10, 2020, Hikma and Dr. Reddy’s, respectively, received U.S. FDA approval to market its generic versions of VASCEPA. During the ANDA litigation, the Company reached agreements with Teva and Apotex, under which they received royalty-free license agreements to promote a generic version of icosapent ethyl in the U.S. under certain circumstances, one of which circumstances was achieved when the Federal Circuit upheld the ruling by the Nevada Court and Hikma launched its generic version of icosapent ethyl. On September 11, 2020, and June 30, 2021, Teva and Apotex, respectively, received U.S. FDA approval to market their respective generic versions of icosapent ethyl. In November 2020, Hikma priced and launched its generic version of icosapent ethyl. In June 2021, following the denial to hear the Company’s appeal by the U.S. Supreme Court, Dr. Reddy’s announced the price of its generic version of icosapent ethyl and launched its generic version of icosapent ethyl. The generic versions of icosapent ethyl as approved by the U.S. FDA for both Hikma and Dr. Reddy’s pertains to the MARINE indication of VASCEPA, lowering of TG levels in patients with very high TG ( > 500 mg/dL). As of September 30, 2021, neither Teva or Apotex had announced pricing or launched a generic version of icosapent ethyl. Current generic competition, together with past and on-going litigation related to such generic versions of icosapent ethyl are applicable to the U.S. only. The Company did not seek, nor is VAZKEPA approved in Europe for lowering of TG levels in patients with very high TG ( > 500 mg/dL). The active pharmaceutical ingredient in VASCEPA is difficult and time consuming to manufacture, often requires considerable advanced planning and long-term financial commitment, including to manufacturing infrastructure such as dedicated facilities, to ensure sufficient capacity is available when needed. The Company has invested over a decade to develop with individual members of its third-party, active pharmaceutical ingredient supply chain the technical knowhow, manufacturing processes and related regulatory approvals that have helped enable the Company’s suppliers to supply the Company’s need for clinical and commercial supply globally. Based on statements made by generic competitors, Hikma and Dr. Reddy’s, the active pharmaceutical ingredient of VASCEPA needed to manufacture their generic versions of VASCEPA is in limited supply to them. The Company believes all icosapent ethyl generic manufacturers are similarly situated. The Company believes the limited supply of generic icosapent ethyl may be due to such companies’ lack of adequate planning, investment, knowhow and expertise regarding this fragile active ingredient. In November 2020, the Company filed a patent infringement lawsuit against Hikma in the United States District Court in Delaware. The complaint alleges that Hikma induced the infringement of VASCEPA-related cardiovascular risk reduction U.S. Patent Nos. 9,700,537 (Composition for preventing the occurrence of cardiovascular event in multiple risk patient), 8,642,077 (Stable pharmaceutical composition and methods of using same), and 10,568,861 (Methods of reducing the risk of a cardiovascular event in a subject at risk for cardiovascular disease) by making, selling, offering to sell and importing generic icosapent ethyl capsules in or into the United States. The Company is seeking remedies including a permanent injunction against Hikma’s unlawful inducement of infringing uses of its generic product to reduce cardiovascular risk and monetary damages in an amount sufficient to compensate the Company for such infringement. In January 2021, the Company expanded the scope of the VASCEPA CV risk reduction patent infringement lawsuit against Hikma to include a health care insurance provider in the United States, Health Net, LLC or Health Net. Through insurance coverage and economic incentives the Company alleges that Health Net has actively induced pharmacies to dispense, and patients to use, Hikma generic icosapent ethyl capsules in infringement of the related patents. In the complaint, the Company is seeking remedies including a permanent injunction against the unlawful inducement by Hikma and Health Net of infringing uses of the Hikma generic product, i.e., uses to reduce cardiovascular risk as detailed in the patents, and monetary damages in an amount sufficient to compensate the Company for such infringement. The Company is considering its legal options against parties similarly situated to Health Net and Hikma and acting in concert with either by making or selling any drug product or component thereof covered by the subject patents, or inducing others to do the same. As has been a practice in the generic pharmaceutical industry, on April 27, 2021, Dr. Reddy’s filed a complaint against the Company in the United States District Court for the District of New Jersey, Civil action No.21-cv-10309, alleging various antitrust violations stemming from alleged anticompetitive practices related to the supply of active pharmaceutical ingredient of VASCEPA. The complaint also includes a related state law tortious interference claim. Damages sought include recovery for alleged economic harm to Dr. Reddy’s, payors and consumers, treble damages and other costs and fees. Injunctive relief against the alleged violative activities is also being sought by Dr. Reddy’s. Amarin believes it has valid defenses and will vigorously defend against the claims. Amarin received a civil investigative demand from the U.S. Federal Trade Commission and a subpoena from the New York Attorney General with respect to information on the same antitrust topic covered in the Dr. Reddy's litigation. The Company believes such contact from the governments may have been prompted by a generic competitor. Amarin is cooperating with the government agencies. As has been a practice of class action legal counsel following governmental investigations and litigation by generics companies, Amarin is also named as a defendant in five antitrust class action lawsuits in the District Court for the District of New Jersey. Amarin is a defendant in a class action lawsuit filed by Uniformed Fire Officers Association Family Protection Plan Local 854 and the Uniformed Fire Officers Association for Retired Fire Officers Family Protection Plan, on behalf of indirect purchasers, in the District Court for the District of New Jersey, Civil Action No. 21-12061, alleging Amarin and its co-defendant suppliers violated state and federal antitrust laws by monopolizing and engaging in a conspiracy to restrain trade in the icosapent ethyl drug and API markets. Amarin is a defendant in a class action lawsuit filed by The International Union of Operating Engineers Locals 137, 137A, 137B, 137C, 137R, on behalf of indirect purchasers, in the District Court for the District of New Jersey, Civil Action No. 21-12416, alleging Amarin violated state and federal antitrust laws by monopolizing and engaging in a conspiracy to restrain trade in the icosapent ethyl drug and API markets. Amarin is a defendant in a class action lawsuit filed by KPH Healthcare Services, Inc., on behalf of direct purchasers, in the District Court for the District of New Jersey, Civil Action No. 21-12747, alleging Amarin and its co-defendant suppliers violated state and federal antitrust laws by monopolizing and engaging in a conspiracy to restrain trade in the icosapent ethyl drug and API markets. Amarin is a defendant in a class action lawsuit filed by Local 464A United Food and Commercial Workers Union Welfare Service Benefit Fund, on behalf of direct purchasers, in the District Court for the District of New Jersey, Civil Action No. 21-13009. Amarin is a defendant in a class action lawsuit filed by Teamsters Health & Welfare Fund of Philadelphia and Vicinity, on behalf of indirect purchasers, in the District Court for the District of New Jersey, Civil Action No. 21-13406, alleging Amarin violated state and federal antitrust laws by monopolizing and engaging in a conspiracy to restrain trade in the icosapent ethyl drug and API markets. Such antitrust litigation and investigations can be lengthy, costly and could materially affect and disrupt the Company’s business. The Company cannot predict when these matters will be resolved, their outcome or their potential impact on the Company’s business. If a government determines that Amarin has violated antitrust law, the Company could be subject to significant civil fines and penalties. The Company intends to vigorously enforce its intellectual property rights relating to VASCEPA, but cannot predict the outcome of these lawsuits or any subsequently filed lawsuits. Litigation – Other On February 22, 2019, a purported investor in the Company’s publicly traded securities filed a putative class action lawsuit against Amarin Corporation plc, the chief executive officer and chief scientific officer in the U.S. District Court for the District of New Jersey, Debendra Sharma v. Amarin Corporation plc, John F. Thero and Steven Ketchum, No. 2:19-cv-06601 (D.N.J. Feb. 22, 2019). On March 12, 2019, another purported investor filed a substantially similar lawsuit captioned Richard Borghesi v. Amarin Corporation plc, John F. Thero and Steven Ketchum, No. 3:19-cv-08423 (D.N.J. March 12, 2019). On May 14, 2019 the court consolidated the cases under the caption In re Amarin Corporation PLC Securities Litigation, No. 3:19-cv-06601 and appointed two other purported shareholders, Dan Kotecki and the Gaetano Cecchini Living Trust, as Co-Lead Plaintiffs. Co-Lead Plaintiffs filed a consolidated amended complaint, or Amended Complaint, on July 22, 2019 that added as defendants the Company’s former chief medical officer and the Company’s former chief executive officer. The Amended Complaint alleged that from September 24, 2018 to November 9, 2018 the Company misled investors by releasing topline results for the REDUCE-IT study without disclosing data on biomarker increases in the placebo group as compared with baseline measurement. The Amended Complaint alleged that these data suggest that the mineral oil placebo used in the REDUCE-IT study may have interfered with statin absorption in the placebo group, which they alleged may have increased adverse outcomes in the placebo group. The Amended Complaint further alleged that these purported misrepresentations and omissions inflated the share price. Based on these allegations, the suit asserted claims under the Securities Exchange Act of 1934 and sought unspecified monetary damages and attorneys’ fees and costs. On March 29, 2021, the court granted the Company’s motion to dismiss this litigation for failure to state a valid claim. The litigation was dismissed without prejudice, giving the plaintiffs the right to file an amended complaint. Plaintiffs in this action did not file an amended complaint within the permitted filing deadline. Plaintiffs filed a notice of appeal of the motion to dismiss ruling, which has been denominated In re: Amarin Corp. PLC , case number 21-2071 (3d Cir.). The Company intends to vigorously defend against any future complaint in this matter. On October 21, 2021, a purported investor in the Company's publicly traded securities filed a putative class action lawsuit against Amarin Corporation plc, the former chief executive officer and the chief financial officer in the U.S. District Court for the District of New Jersey, Vincent Dang v. Amarin Corporation plc, John F. Thero and Michael W. Kalb, No. 1:21-cv-19212 (D.N.J. Oct. 21, 2021). The complaint alleges that from December 5, 2018 through June 21, 2021 the Company misled investors by allegedly downplaying the risk associated with the ANDA litigation described above and the risk that certain of the Company's patents would be invalidated. Based on these allegations, plaintiff alleges that he purchased securities at an inflated share price and brings claims under the Securities and Exchange Act of 1934 seeking unspecified monetary damages and attorneys' fees and costs. We believe we have valid defenses and will vigorously defend against the claims but cannot predict the outcome. In addition to the above, in the ordinary course of business, the Company is from time to time involved in lawsuits, claims, investigations, proceedings, and threats of litigation relating to intellectual property, commercial arrangements and other matters. Milestone and Supply Purchase Obligations The Company entered into long-term supply agreements with multiple API suppliers and encapsulators. The Company is relying on these suppliers to meet current and potential future global demand for its lead product. Certain supply agreements require annual minimum volume commitments by the Company and certain volume shortfalls may require payments for such shortfalls. These agreements include requirements for the suppliers to meet certain product specifications and qualify their materials and facilities with applicable regulatory authorities, including the U.S. FDA. The Company has incurred certain costs associated with the qualification of product produced by these suppliers. Pursuant to the supply agreements, there is a total of approximately $ 213.0 million that is potentially payable over the term of such agreements based on minimum purchase obligations. The Company continues to meet its contractual purchase obligations. On March 26, 2021, the EC approved the marketing authorization application for VAZKEPA. Under the 2004 share repurchase agreement with Laxdale, upon receipt of pricing approval in Europe for the first indication for VASCEPA (or first indication of any product containing intellectual property acquired from Laxdale in 2004), the Company must make an aggregate stock or cash payment to the former shareholders of Laxdale (at the sole option of each of the sellers) of £ 7.5 million. The Company recorded a liability of $ 12.0 million in Accrued expenses and other current liabilities on the condensed consolidated balance sheet as of September 30, 2021. Also under the Laxdale agreement, upon receipt of a marketing approval in Europe for a further indication of VASCEPA (or further indication of any other product acquired from Laxdale in 2004), the Company must make an aggregate stock or cash payment (at the sole option of each of the sellers) of £ 5 million (approximately $ 6.7 million as of September 30, 2021) for the potential market approval. The Company has no provision for any of these obligations, except as noted above, since the amounts are either not paid or payable as of September 30, 2021 .

Equity

Equity	9 Months Ended
	Sep. 30, 2021
Equity [Abstract]
Equity	(6) Equity Preferred Stock In March 2015, the Company entered into subscription agreements with both existing and new investors, or the Purchasers, for the private placement of a total of 391,017,970 restricted American Depositary Shares, or ADSs, each representing one share of Amarin’s Series A Convertible Preference Shares , par value £ 0.05 per share, in the capital of the Company, or Series A Preference Shares. For each restricted ADS, the Purchasers paid a negotiated price of $ 0.15 (equating to $ 1.50 on an as-if-converted-to-ordinary-shares basis), resulting in gross proceeds to the Company of approximately $ 58.6 million before deducting estimated offering expenses of approximately $ 0.7 million. At the request of the holders and provided certain conditions were met, each ten Series A Preference Shares were able to be consolidated and redesignated as one ordinary share, par value £ 0.50 per share, in the capital of the Company, each ordinary share to be represented by ADSs. During the years ended December 31, 2020, 2018, and 2015, the Company issued 28,931,746 , 3,886,718 , and 6,283,333 ADSs, respectively, upon consolidation and redesignation of Series A Preference Shares at the request of the holders, such that no Series A Preference Shares remained outstanding as of September 30, 2021 and December 31, 2020. Refer to the Company’s Annual Report on Form 10-K for the year ended December 31, 2020 for a more complete background. Common Stock During the nine months ended September 30, 2021 and 2020, in addition to ordinary shares issued as described in Preferred Stock above and Incentive Equity Awards below, the Company issued 226,402 and 123,608 ordinary shares, respectively, under the Amarin Corporation plc 2017 Employee Stock Purchase Plan. Incentive Equity Awards The following table summarizes the aggregate number of stock options and restricted stock units, or RSUs, outstanding under the Amarin Corporation plc 2020 Stock Incentive Plan, or the 2020 Plan, as of September 30, 2021: September 30, 2021 Outstanding Stock Options 19,145,833 % of Outstanding Shares 5 % Outstanding RSUs 10,307,168 % of Outstanding Shares 2 % The following table represents equity awards activity during the nine months ended September 30, 2021 and 2020: For the Nine Months Ended September 30, 2021 2020 Stock Options Issued 994,921 642,756 Gross Proceeds $ 2,616,050 $ 1,861,000 Common Shares Issued in settlement of RSUs Vested 1,202,590 1,206,494 Shares retained for settlement of employee tax obligations ─ RSUs 454,973 440,573 Common Shares Issued in settlement of Performance-Based RSUs Vested (1) 1,923,316 1,107,660 Shares retained for settlement of employee tax obligations ─ Performance-Based RSUs 816,931 461,820 (1) Performance-based RSUs vested in connection with the achievement of certain regulatory and sales performance conditions associated with the REDUCE-IT clinical trial and subsequent revenue growth. These performance-based RSUs have fully vested as of August 2021. On June 14, 2021, the Company granted a total of 218,000 RSUs and 278,271 stock options to members of the Company’s Board of Directors under the 2020 Plan. The RSUs vest in equal installments over a three-year period upon the earlier of the anniversary of the grant date or the Company’s annual general meeting of shareholders in such anniversary year, and are subject to deferred settlement upon the Director’s separation of service with the Company. The stock options vest in full upon the earlier of the one-year anniversary of the grant date or the Company’s annual general meeting of shareholders in such anniversary year. Upon termination of service to the Company or upon a change of control, each director shall be entitled to a payment equal to the fair market value of one share of Amarin common stock per award vested or granted, respectively, which is required to be made in shares. On January 4, 2021, the Company granted a total of 3,265,700 RSUs and 3,100,200 stock options to employees under the 2020 Plan. The RSUs vest annually over a three-year period and the stock options vest quarterly over a four-year period with a one-year cliff vesting. Also on January 4, 2021, the Company granted a total of 1,345,800 RSUs to certain employees under the 2020 Plan that vest upon the achievement of specified operational performance conditions. On June 1, 2020, the Company granted a total of 782,520 RSUs to employees under the Amarin Corporation plc 2011 Stock Incentive Plan, or the 2011 Plan. The RSUs vest quarterly over a three-year period. On March 2, 2020 and February 3, 2020, the Company granted a total of 821,950 RSUs and 1,875,000 stock options, respectively, to employees under the 2011 Plan. The RSUs vest annually over a three-year period and the stock options vest quarterly over a four-year period. Also on February 3, 2020, the Company granted a total of 1,253,400 RSUs to employees under the 2011 Plan that vest upon the achievement of specified sales performance conditions.

Co-Promotion Agreement

Co-Promotion Agreement	9 Months Ended
	Sep. 30, 2021
Co Promotion Agreement [Abstract]
Co-Promotion Agreement	(7) Co-Promotion Agreement On March 31, 2014, the Company entered into a Co-Promotion Agreement, or the Agreement, with Kowa Pharmaceuticals America, Inc. related to the commercialization of VASCEPA capsules in the United States. The Company and Kowa Pharmaceuticals America, Inc. intentionally designed the Agreement to naturally end as of December 31, 2018 and mutually agreed not to renew the Agreement. During 2018, which was the last year of the co-promotion of VASCEPA by Kowa Pharmaceuticals America, Inc., the Company incurred expense for co-promotion tail payments which are calculated as a percentage of the 2018 co-promotion fee, which was eighteen and a half percent ( 18.5 %) of VASCEPA gross margin in 2018. The accrued tail payments are paid over three years with declining amounts each year. Kowa Pharmaceuticals America, Inc. was eligible to receive $ 17.8 million in co-promotion tail payments, the present value of which $ 16.6 million, was fully accrued as of December 31, 2018. As of September 30, 2021, a net payable to Kowa Pharmaceuticals America, Inc. of $ 1.3 million was classified as current on the condensed consolidated balance sheet, representing the remaining accrued co-promotion tail payments. As of December 31, 2020, a net payable to Kowa Pharmaceuticals America, Inc. of $ 3.8 million, of which $ 3.2 million was classified as current on the condensed consolidated balance sheet, represents the remaining accrued co-promotion tail payments.

Revenue Recognition

Revenue Recognition	9 Months Ended
	Sep. 30, 2021
Revenue from Contract with Customer [Abstract]
Revenue Recognition	(8) Revenue Recognition The Company sells VASCEPA principally to a limited number of major wholesalers, as well as selected regional wholesalers and specialty pharmacy providers in the United States and Europe, or collectively, its distributors or its customers, that in turn resell VASCEPA to retail pharmacies for subsequent resale to patients and healthcare providers. Patients are required to have a prescription in order to purchase VASCEPA. In addition to distribution agreements with distributors, the Company enters into arrangements with health care providers and payors that provide for government-mandated and/or privately-negotiated rebates, chargebacks and discounts with respect to the purchase of the Company’s product. Revenues from product sales are recognized when the distributor obtains control of the Company’s product, which occurs at a point in time, typically upon delivery to the distributor. Payments from distributors are generally received 30 - 60 days from the date of sale. The Company evaluates the creditworthiness of each of its distributors to determine whether revenues can be recognized upon delivery, subject to satisfaction of the other requirements, or whether recognition is required to be delayed until receipt of payment . The Company calculates gross product revenues generally based on the wholesale acquisition cost or list price that the Company charges its distributors for VASCEPA. Reserves for Variable Consideration Revenues from product sales are recorded at the net sales price (transaction price), which includes estimates of variable consideration for which reserves are established and which result from (a) trade allowances, such as invoice discounts for prompt pay and distributor fees, (b) estimated government and private payor rebates and chargebacks and discounts, such as Medicaid reimbursements, (c) reserves for expected product returns and (d) estimated costs of incentives that are offered within contracts between the Company and its distributors, health care providers, payors and other indirect customers relating to the Company’s sales of its product. These reserves are based on the amounts earned or to be claimed on the related sales and are classified as reductions of accounts receivable (if the amount is payable to the distributor) or as a current liability (if the amount is payable to a party other than a distributor). Where appropriate, these estimates take into consideration a range of possible outcomes which are probability-weighted for relevant factors such as the Company’s historical experience, current contractual and statutory requirements, specific known market events and trends, industry data and forecasted customer buying and payment patterns. Overall, these reserves reflect the Company’s best estimates of the amount of consideration to which it is entitled based on the terms of the contract. The amount of variable consideration which is included in the transaction price may be constrained, and is included in the net sales price only to the extent that it is probable that a significant reversal in the amount of the cumulative revenue recognized will not occur in a future period. Actual amounts of consideration ultimately received may differ from the Company’s estimates. If actual results in the future vary from the Company’s estimates, the Company adjusts these estimates, which would affect net product revenue and earnings in the period such variances become known. Trade Allowances: The Company generally provides invoice discounts on VASCEPA sales to its distributors for prompt payment and fees for distribution services, such as fees for certain data that distributors provide to the Company. The payment terms for sales to distributors in the U.S. and Germany generally include a 2 - 3 % discount for prompt payment while the fees for distribution services are based on contractual rates agreed with the respective distributors. Based on historical data, the Company expects its distributors to earn these discounts and fees, and deducts the full amount of these discounts and fees from its gross product revenues and accounts receivable at the time such revenues are recognized. Rebates, Chargebacks and Discounts: The Company contracts with Medicaid, Medicare, other government agencies and various private organizations, or collectively, Third-party Payors, so that VASCEPA will be eligible for purchase by, or partial or full reimbursement from, such Third-party Payors. The Company estimates the rebates, chargebacks and discounts it will provide to Third-party Payors and deducts these estimated amounts from its gross product revenues at the time the revenues are recognized. The Company estimates these reserves based upon a range of possible outcomes that are probability-weighted for the estimated payor mix. These reserves are recorded in the same period the revenue is recognized, resulting in a reduction of product revenue and the establishment of a current liability, which is included in Accrued expenses and other current liabilities on the condensed consolidated balance sheets. For Medicare, the Company also estimates the number of patients in the prescription drug coverage gap for whom the Company will owe an additional liability under the Medicare Part D program. The Company estimates the rebates, chargebacks and discounts that it will provide to Third-party Payors based upon (i) the Company’s contracts with these Third-party Payors, (ii) the government-mandated discounts applicable to government-funded programs, (iii) information obtained from the Company’s distributors and (iv) information obtained from other third parties regarding the payor mix for VASCEPA. The Company’s liability for these rebates consists of invoices received for claims from prior quarters that have not been paid or for which an invoice has not yet been received, estimates of claims for the current quarter, and estimated future claims that will be made for product that has been recognized as revenue, but remains in the distribution channel inventories at the end of each reporting period. Product Returns: The Company’s distributors have the right to return unopened unprescribed VASCEPA during the 18-month period beginning six months prior to the labeled expiration date and ending 12 months after the labeled expiration date. The expiration date for VASCEPA 1-gram and 0.5-gram size capsules is currently four years and three years , respectively, after being converted into capsule form, which is the last step in the manufacturing process for VASCEPA and generally occurs within a few months before VASCEPA is delivered to distributors. The Company estimates future product returns on sales of VASCEPA based on: (i) data provided to the Company by its distributors (including weekly reporting of distributors’ sales and inventory held by distributors that provided the Company with visibility into the distribution channel in order to determine what quantities were sold to retail pharmacies and other providers), (ii) information provided to the Company from retail pharmacies, (iii) data provided to the Company by a third-party data provider which collects and publishes prescription data, and other third parties, (iv) historical industry information regarding return rates for similar pharmaceutical products, (v) the estimated remaining shelf life of VASCEPA previously shipped and currently being shipped to distributors and (vi) contractual agreements intended to limit the amount of inventory maintained by the Company’s distributors. These reserves are recorded in the same period the related revenue is recognized, resulting in a reduction of product revenue and the establishment of a current liability which is included in Accrued expenses and other current liabilities on the condensed consolidated balance sheets. Other Incentives: Other incentives that the Company offers to indirect customers include co-pay mitigation rebates provided by the Company to commercially insured patients who have coverage for VASCEPA and who reside in states that permit co-pay mitigation programs. The Company’s co-pay mitigation program is intended to reduce each participating patient’s portion of the financial responsibility for VASCEPA’s purchase price to a specified dollar amount. Based upon the terms of the program and information regarding programs provided for similar specialty pharmaceutical products, the Company estimates the average co-pay mitigation amounts and the percentage of patients that it expects to participate in the program in order to establish its accruals for co-pay mitigation rebates. These reserves are recorded in the same period the related revenue is recognized, resulting in a reduction of product revenue and the establishment of a current liability which is included in Accrued expenses and other current liabilities on the condensed consolidated balance sheets. The Company adjusts its accruals for co-pay mitigation rebates based on actual redemption activity and estimates regarding the portion of issued co-pay mitigation rebates that it estimates will be redeemed. The following tables summarize activity in each of the net product revenue allowance and reserve categories described above for the nine months ended September 30, 2021 and 2020: In thousands Trade Rebates, Product Other Total Balance as of December 31, 2020 $ 36,242 $ 141,201 $ 7,797 $ 5,587 $ 190,827 Provision related to current period sales 90,761 497,726 2,647 36,437 627,571 Provision related to prior period sales — ( 854 ) — — ( 854 ) Credits/payments made for current period sales ( 27,635 ) ( 303,029 ) — ( 31,796 ) ( 362,460 ) Credits/payments made for prior period sales ( 34,511 ) ( 131,320 ) ( 958 ) ( 5,589 ) ( 172,378 ) Balance as of September 30, 2021 $ 64,857 $ 203,724 $ 9,486 $ 4,639 $ 282,706 In thousands Trade Rebates, Product Other Total Balance as of December 31, 2019 $ 29,261 $ 90,997 $ 4,579 $ 3,720 $ 128,557 Provision related to current period sales 95,239 437,030 2,534 50,403 585,206 Provision related to prior period sales — ( 3,872 ) — — ( 3,872 ) Credits/payments made for current period sales ( 32,364 ) ( 304,903 ) — ( 46,768 ) ( 384,035 ) Credits/payments made for prior period sales ( 29,067 ) ( 85,731 ) ( 223 ) ( 3,721 ) ( 118,742 ) Balance as of September 30, 2020 $ 63,069 $ 133,521 $ 6,890 $ 3,634 $ 207,114 Such net product revenue allowances and reserves are included within Accrued expenses and other current liabilities within the condensed consolidated balance sheets, with the exception of trade allowances and chargebacks, which are included within Accounts receivable, net as discussed above. Licensing Revenue The Company enters into licensing agreements which are within the scope of Topic 606, under which it licenses certain rights to VASCEPA for uses that are currently commercialized and under development by the Company. The terms of these arrangements typically include payment to the Company of one or more of the following: non-refundable, up-front license fees; development, regulatory and commercial milestone payments; payments for manufacturing supply services the Company provides through its contract manufacturers; and royalties on net sales of licensed products. Each of these payments results in licensing and royalty revenues. In determining the appropriate amount of revenue to be recognized as it fulfills its obligations under each of its agreements, the Company performs the following steps: (i) identification of the promised goods or services in the contract; (ii) determination of whether the promised goods or services are performance obligations including whether they are distinct in the context of the contract; (iii) measurement of the transaction price, including the constraint on variable consideration; (iv) allocation of the transaction price to the performance obligations; and (v) recognition of revenue when (or as) the Company satisfies each performance obligation. In determining performance obligations, management evaluates whether the license is distinct from the other performance obligations with the collaborative partner based on the consideration of the relevant facts and circumstances for each arrangement. Factors considered in the determination include the stage of development of the license delivered, research and development capabilities of the partner and the ability of partners to develop and commercialize VASCEPA independent of the Company. Licenses of intellectual property: If the license to the Company’s intellectual property is determined to be distinct from the other performance obligations identified in the arrangement, the Company recognizes revenues from non-refundable, up-front fees allocated to the license when the license is transferred to the customer and the customer is able to use and benefit from the license. For licenses that are bundled with other promises, the Company utilizes judgment to assess the nature of the combined performance obligation to determine whether the combined performance obligation is satisfied over time or at a point in time and, if over time, the appropriate method of measuring progress for purposes of recognizing revenue from non-refundable, up-front fees. The Company evaluates the measure of progress each reporting period and, if necessary, adjusts the measure of performance and related revenue recognition. Milestone Payments: At the inception of each arrangement that includes development, regulatory and commercial milestone payments, the Company evaluates whether the milestones are considered probable of being reached and estimates the amount to be included in the transaction price using the most likely amount method. If it is probable that a significant revenue reversal would not occur, the associated milestone value is included in the transaction price. Milestone payments that are not within the control of the Company or licensee, such as regulatory approvals, are not considered probable of being achieved until those approvals are received. The Company evaluates factors such as the scientific, clinical, regulatory, commercial and other risks that must be overcome to achieve the respective milestone as well as the level of effort and investment required. The transaction price is then allocated to each performance obligation on a relative stand-alone selling price basis, for which the Company recognizes revenue as or when the performance obligations under the contract are satisfied. At the end of each subsequent reporting period, the Company re-evaluates the probability of achievement of such development, regulatory and commercial milestones and any related constraint, and if necessary, adjusts its estimate of the overall transaction price. Any such adjustments are recorded on a cumulative catch-up basis, which would affect licensing revenues and earnings in the period of adjustment. The Company receives payments from its customers based on billing schedules established in each contract. Up-front payments and fees are recorded as deferred revenue upon receipt or when due, and may require deferral of revenue recognition to a future period until the Company performs its obligations under these arrangements. Amounts are recorded as accounts receivable when the Company’s right to consideration is unconditional. The Company does not assess whether a contract has a significant financing component if the expectation at contract inception is such that the period between payment by the customer and the transfer of the promised goods or services to the customer will be one year or less.

Development, Commercialization

Development, Commercialization and Supply Agreements	9 Months Ended
	Sep. 30, 2021
Organization, Consolidation and Presentation of Financial Statements [Abstract]
Development, Commercialization and Supply Agreements	(9) Development, Commercialization and Supply Agreements In-licenses Mochida Pharmaceutical Co., Ltd. In June 2018, the Company entered into a collaboration with Mochida Pharmaceutical Co., Ltd., or Mochida, related to the development and commercialization of drug products and indications based on the active pharmaceutical ingredient in VASCEPA, the omega-3 acid, EPA, or eicosapentaenoic acid. Among other terms in the agreement, the Company obtained an exclusive license to certain Mochida intellectual property to advance the Company’s interests in the United States and certain other territories and the parties will collaborate to research and develop new products and indications based on EPA for the Company’s commercialization in the United States and certain other territories. The potential new product and indication opportunities contemplated under this agreement are currently in early stages of development. Upon closing of the collaboration agreement, the Company made a non-refundable, non-creditable upfront payment of approximately $ 2.7 million. In addition, the agreement provides for the Company to pay milestone payments upon the achievement of certain product development milestones and royalties on net sales of future products arising from the collaboration, if any. In January 2021, the Company exercised certain rights under the agreement, resulting in a payment of $ 1.0 million to Mochida, which was recorded as Research and development expense in the condensed consolidated statement of operations. In January 2020 and December 2020, the Company exercised certain rights under the agreement, resulting in payments of $ 1.0 million, respectively, to Mochida, which were recorded as Research and development expense in the condensed consolidated statement of operations. Out-licenses Eddingpharm (Asia) Macao Commercial Offshore Limited In February 2015, the Company entered into a Development, Commercialization and Supply Agreement, or the DCS Agreement, with Eddingpharm (Asia) Macao Commercial Offshore Limited, or Edding, related to the development and commercialization of VASCEPA in Mainland China, Hong Kong, Macau and Taiwan, or the China Territory. Under the terms of the DCS Agreement, the Company granted to Edding an exclusive (including as to the Company) license with right to sublicense to develop and commercialize VASCEPA in the China Territory for uses that are currently commercialized and under development by the Company based on the Company’s MARINE, ANCHOR and REDUCE-IT clinical trials of VASCEPA. Under the DCS Agreement, Edding is solely responsible for development and commercialization activities in the China Territory and associated expenses. The Company provides development assistance and is responsible for supplying finished and later bulk drug product at defined prices under negotiated terms. The Company retains all VASCEPA manufacturing rights. Edding agreed to certain restrictions regarding the commercialization of competitive products globally and the Company agreed to certain restrictions regarding the commercialization of competitive products in the China Territory. The Company and Edding agreed to form a joint development committee to oversee regulatory and development activities for VASCEPA in the China Territory in accordance with a negotiated development plan and formed a separate joint commercialization committee in advance of expected approval in the China Territory to oversee VASCEPA planning and pre-launch commercialization activities in the China Territory. Development costs are paid by Edding to the extent such costs are incurred in connection with the negotiated development plan or otherwise incurred by Edding. Edding is responsible for preparing and filing regulatory applications in all countries of the China Territory at Edding’s cost with the Company’s assistance. The DCS Agreement also contains customary provisions regarding indemnification, supply, record keeping, audit rights, reporting obligations, and representations and warranties that are customary for an arrangement of this type. The term of the DCS Agreement expires, on a product-by-product basis, upon the later of (i) the date on which such product is no longer covered by a valid claim under a licensed patent in the China Territory, or (ii) the 12th anniversary of the first commercial sale of such product in Mainland China. The DCS Agreement may be terminated by either party in the event of a bankruptcy of the other party and for material breach, subject to customary cure periods. In addition, at any time following the third anniversary of the first commercial sale of a product in Mainland China, Edding has the right to terminate the DCS Agreement for convenience with 12 months’ prior notice. Neither party may assign or transfer the DCS Agreement without the prior consent of the other party, provided that the Company may assign the DCS Agreement in the event of a change of control transaction. Upon closing of the DCS Agreement, the Company received a non-refundable $ 15.0 million up-front payment. In March 2016, Edding submitted its clinical trial application, or CTA, with respect to the MARINE indication for VASCEPA to the Chinese regulatory authority. Following the CTA submission, the Company received a non-refundable $ 1.0 million milestone payment. In March 2017, the CTA was approved by the Chinese regulatory authority, and, in December 2017, Edding commenced a pivotal clinical trial aimed to support the regulatory approval of the first indication of VASCEPA in a patient population with severe hypertriglyceridemia in Mainland China. In November 2020, the Company announced statistically significant topline results from the Phase 3 clinical trial of VASCEPA conducted by Edding, which is being used to seek regulatory approval in Mainland China. Edding is also seeking regulatory approval of VASCEPA in Hong Kong. In addition to the non-refundable, up-front and regulatory milestone payments described above, the Company is entitled to receive certain regulatory and sales-based milestone payments of up to an additional $ 153.0 million as well as tiered double-digit percentage royalties on net sales of VASCEPA in the China Territory escalating to the high teens. The regulatory milestone events relate to the submission and approval of certain applications to the applicable regulatory authority, such as a clinical trial application, clinical trial exemption, or import drug license application. The amounts to be received upon achievement of the regulatory milestone events relate to the submission and approval for three indications, and range from $ 2.0 million to $ 15.0 million for a total of $ 33.0 million. The sales-based milestone events occur when annual aggregate net sales of VASCEPA in the territory equals or exceeds certain specified thresholds, and range from $ 5.0 million to $ 50.0 million for a total of $ 120.0 million. Each such milestone payment shall be payable only once regardless of how many times the sales milestone event is achieved. Each such milestone payment is non-refundable and non-creditable against any other milestone payments. The Company assessed this arrangement in accordance with Topic 606 and concluded that the contract counterparty, Edding, is a customer. The Company identified the following performance obligations at the inception of the DCS Agreement: (1) the exclusive license to develop and commercialize VASCEPA in the China Territory for uses that are currently commercialized and under development by the Company, (2) the obligation to participate in various steering committees, and (3) ongoing development and regulatory assistance. Based on the analysis performed, the Company concluded that the identified performance obligations are not distinct and therefore a combined performance obligation. The transaction price includes the $ 15.0 million up-front consideration received and the $ 1.0 million milestone payment received related to the successful submission of the CTA for the MARINE indication. None of the other clinical or regulatory milestones have been included in the transaction price, as all milestone amounts are fully constrained. As part of its evaluation of the constraint, the Company considered numerous factors, including that receipt of the milestones is outside the control of the Company and contingent upon success in future clinical trials and the licensee’s efforts. Any consideration related to sales-based milestones, including royalties, will be recognized when the related sales occur and therefore have also been excluded from the transaction price. The Company will re-evaluate the transaction price in each reporting period and as uncertain events are resolved or other changes in circumstances occur. During the nine months ended September 30, 2021 and 2020, the Company recognized $ 0.8 million and $ 2.2 million, respectively, as licensing revenue related to the up-front and milestone payments received in connection with the Edding agreement. From contract inception through September 30, 2021 and December 31, 2020, the Company recognized $ 6.9 million and $ 6.1 million, respectively, as licensing revenue under the DCS Agreement concurrent with the input measure of support hours provided by Amarin to Edding in achieving the combined development and regulatory performance obligation, which in the Company’s judgment is the best measure of progress towards satisfying this performance obligation. The remaining transaction price of $ 10.0 million and $ 10.8 million is recorded in deferred revenue as of September 30, 2021 and December 31, 2020 , respectively, on the condensed consolidated balance sheets and will be recognized as revenue over the remaining period of 13 years . Biologix FZCo In March 2016, the Company entered into an agreement with Biologix FZCo, or Biologix, a company incorporated under the laws of the United Arab Emirates, to register and commercialize VASCEPA in several Middle Eastern and North African countries. Under the terms of the distribution agreement, the Company granted to Biologix a non-exclusive license to use its trademarks in connection with the importation, distribution, promotion, marketing and sale of VASCEPA in the Middle East and North Africa territory. Upon closing of the agreement, the Company received a non-refundable up-front payment, which will be recognized as revenue over 10 years commencing upon first marketing approval of VASCEPA in the territory. The Company is entitled to receive all payments based on total product sales and pays Biologix a service fee in exchange for its services, whereby the service fee represents a percentage of gross selling price which is subject to a minimum floor price. The Company received approval of VASCEPA as a prescription medication for use in Lebanon in March 2018, in United Arab Emirates in July 2018, in Qatar in January 2020 and in Bahrain in December 2020 as an adjunct to diet to reduce triglyceride levels in adult patients with severe hypertriglyceridemia. VASCEPA was launched in Lebanon in June 2018 and in United Arab Emirates in February 2019. The Company recognized net product revenue of approximately $ 0.5 million and $ 1.0 million for the three and nine months ended September 30, 2021, respectively, and $ 0.5 million for the three and nine months ended September 30, 2020, respectively, related to sales to Biologix. HLS Therapeutics, Inc. In September 2017, the Company entered into an agreement with HLS Therapeutics Inc., or HLS, a company incorporated under the laws of Canada, to register, commercialize and distribute VASCEPA in Canada. Under the agreement, HLS will be responsible for regulatory and commercialization activities and associated costs. The Company is responsible for providing assistance towards local filings, supplying finished product under negotiated supply terms, maintaining intellectual property, and continuing the development and funding of REDUCE-IT related activities. Upon closing of the agreement, the Company received one-half of a non-refundable $ 5.0 million up-front payment, and received the remaining half on the six-month anniversary of the closing. Following achievement of the REDUCE-IT trial primary endpoint, which was announced in September 2018, the Company received a non-refundable $ 2.5 million milestone payment. Following approval from Health Canada in December 2019, the Company received a non-refundable milestone payment of $ 2.5 million in February 2020. In addition, in January 2020 HLS obtained regulatory exclusivity from the Office of Patented Medicines and Liaison, or OPML, as a result the Company received a non-refundable $ 3.8 million milestone payment. In addition to the non-refundable, up-front and regulatory milestone payments just described, the Company is entitled to receive certain sales-based milestone payments of up to an additional $ 50.0 million, as well as tiered double-digit royalties on net sales of VASCEPA in Canada. The Company assessed this arrangement in accordance with Topic 606 and concluded that the contract counterparty, HLS, is a customer. The Company identified the following performance obligations at the inception of the contract: (1) license to HLS to develop, register, and commercialize VASCEPA in Canada, (2) support general development and regulatory activities, and (3) participate in various steering committees. Based on the analysis performed, the Company concluded that the identified performance obligations in the agreement are not distinct and therefore a combined performance obligation. The transaction price includes the $ 5.0 million up-front consideration, the $ 2.5 million milestone related to the achievement of the REDUCE-IT trial primary endpoint, the $ 2.5 million milestone related to obtaining approval from Health Canada and $ 3.8 million milestone related to obtaining regulatory exclusivity from the OPML. Any consideration related to sales-based milestones (including royalties) will be recognized when the related sales occur and therefore have also been excluded from the transaction price. The Company will re-evaluate the transaction price in each reporting period and as uncertain events are resolved or other changes in circumstances occur. During the nine months ended September 30, 2021 and 2020, the Company recognized $ 0.7 million and $ 3.5 million, respectively, as licensing revenue related to up-front and milestone payments received in connection with the HLS agreement. From the contract’s inception through September 30, 2021 and December 31, 2020, the Company has recognized $ 7.3 million and $ 6.6 million, respectively, as licensing revenue is recognized under the agreement concurrent with the input measure of support hours provided by Amarin to HLS in achieving this performance obligation, which in the Company’s judgment is the best measure of progress towards satisfying the combined development and regulatory performance obligation. The remaining transaction price of $ 6.4 million and $ 7.1 million is recorded in deferred revenue as of September 30, 2021 and December 31, 2020 , respectively, on the condensed consolidated balance sheets and will be recognized as revenue over the remaining period of 9 years . The Company recognized net product revenue of nil for the three months ended September 30, 2021 and 2020, respectively, and nil and $ 8.5 million for the nine months ended September 30, 2021 and 2020, respectively, related to HLS. The following table presents changes in the balances of the Company’s contract assets and liabilities during the nine months ended September 30, 2021 and 2020: In thousands Balance at Additions Deductions Balance at Nine months ended September 30, 2021: Contract assets $ — $ — $ — $ — Contract liabilities: Deferred revenue $ 18,632 $ 92 $ ( 1,592 ) $ 17,132 Nine months ended September 30, 2020: Contract assets $ — $ — $ — $ — Contract liabilities: Deferred revenue $ 20,846 $ 3,750 $ ( 5,691 ) $ 18,905 During the nine months ended September 30, 2021 and 2020, the Company recognized the following revenues as a result of changes in the contract asset and contract liability balances in the respective periods: In thousands Nine months ended September 30, Revenue recognized in the period from: 2021 2020 Amounts included in contract liability at the beginning of the period $ 1,555 $ 3,951 Performance obligations satisfied in previous periods $ 33 $ 1,097

Leases

Leases	9 Months Ended
	Sep. 30, 2021
Leases [Abstract]
Leases	(10) Leases The Company leases office space under operating leases. The lease liability is initially measured at the present value of the lease payments to be made over the lease term. Lease payments are comprised of the fixed and variable payments to be made by the Company to the lessor during the lease term minus any incentives or rebates or abatements receivable by the Company from the lessor or the owner. Payments for non-lease components do not form part of lease payments. The lease term includes renewal options only if these options are specified in the lease agreement and if failure to exercise the renewal option imposes a significant economic penalty for the Company. As there are no significant economic penalties, renewal cannot be reasonably assured and the lease terms for the office space do not include any renewal options. The Company has not entered into any leases with related parties. The Company accounts for short-term leases (i.e., lease term of 12 months or less) by making the short-term lease policy election and will not apply the recognition and measurement requirements of ASC 842. The Company has determined that the rate implicit in the lease is not determinable and the Company does not have borrowings with similar terms and collateral. Therefore, the Company considered a variety of factors, including the Company’s credit rating, observable debt yields from comparable companies with a similar credit profile and the volatility in the debt market for securities with similar terms, in determining that 11.5 % was reasonable to use as the incremental borrowing rate for purposes of the calculation of lease liabilities and a change of 1 % would not result in a material change to the Company’s condensed consolidated financial statements. On February 5, 2019, the Company entered into a lease agreement for new office space in Bridgewater, New Jersey, or the Lease. The Lease commenced on August 15, 2019 , or the Commencement Date, for an 11-year period, with two five-year renewal options. Subject to the terms of the Lease, Amarin will have a one-time option to terminate the agreement effective on the first day of the 97 th month after the Commencement Date upon advance written notice and a termination payment specified in the Lease. Under the Lease, the Company paid monthly rent of approximately $ 0.1 million for the first year following the Commencement Date, and such rent increases by a nominal percentage every year following the first anniversary of the Commencement Date. In addition, Amarin receives certain abatements subject to the limitations in the Lease. The operating lease liability is $ 10.5 million and $ 10.6 million and the operating lease right-of-use asset is $ 7.8 million and $ 8.1 million, as of September 30, 2021 and December 31, 2020, respectively. The lease expense for the three and nine months ended September 30, 2021 is approximately $ 0.5 million and $ 1.5 million, respectively. The lease expense for the three and nine months ended September 30, 2020 is approximately $ 0.4 million and $ 1.2 million, respectively. The table below depicts a maturity analysis of the Company’s undiscounted payments for its operating lease liabilities and their reconciliation with the carrying amount of lease liability presented in the statement of financial position as of September 30, 2021: Undiscounted Remainder of 2021 $ 405 2022 1,774 2023 1,808 2024 1,842 2025 1,876 2026 and thereafter 9,112 Total undiscounted payments $ 16,817 Discount Adjustments $ ( 6,358 ) Current operating lease liability $ 1,730 Long-term operating lease liability $ 8,729

Significant Accounting Polici_2

Significant Accounting Policies (Policies)	9 Months Ended
	Sep. 30, 2021
Accounting Policies [Abstract]
Revenue Recognition	Revenue Recognition In accordance with Accounting Standards Codification, or ASC, Topic 606, Revenue from Contracts with Customers , or Topic 606, the Company recognizes revenue when its customer obtains control of promised goods or services, in an amount that reflects the consideration which the entity expects to receive in exchange for those goods or services. To determine revenue recognition for arrangements that an entity determines are within the scope of Topic 606, the entity performs the following five steps: (i) identify the contract(s) with a customer; (ii) identify the performance obligations in the contract; (iii) determine the transaction price; (iv) allocate the transaction price to the performance obligations in the contract; and (v) recognize revenue when (or as) the entity satisfies a performance obligation. The Company only applies the five-step model to contracts when it is probable that the entity will collect the consideration it is entitled to in exchange for the goods or services it transfers to the customer. At contract inception, once the contract is determined to be within the scope of Topic 606, the Company assesses the goods or services promised within each contract and determines those that are performance obligations and assesses whether each promised good or service is distinct. The Company then recognizes as revenue the amount of the transaction price that is allocated to the respective performance obligation when (or as) the performance obligation is satisfied. For a complete discussion of accounting for net product revenue and licensing revenue, see Note 8—Revenue Recognition.
Cash and Cash Equivalents and Restricted Cash	Cash and Cash Equivalents and Restricted Cash Cash and cash equivalents consist of cash, deposits with banks and short-term highly liquid money market instruments with remaining maturities at the date of purchase of 90 days or less. Restricted cash represents cash and cash equivalents pledged to guarantee repayment of certain expenses which may be incurred for business travel under corporate credit cards held by employees.
Accounts Receivable, net	Accounts Receivable, net Accounts receivable, net, comprised of trade receivables, are generally due within 30 days and are stated at amounts due from customers. The Company recognizes an allowance for losses on accounts receivable in an amount equal to the estimated probable losses net of any recoveries. The allowance is based primarily on assessment of specific identifiable customer accounts considered at risk or uncollectible, as well as an analysis of current receivables aging and expected future write-offs. The expense associated with the allowance for doubtful accounts is recognized as Selling, general, and administrative expense. The Company has not historically experienced any significant credit losses. All customer accounts are actively managed and no losses in excess of amounts reserved are currently expected; however, the Company is monitoring the potential negative impact of COVID-19 on the Company’s customers’ ability to meet their financial obligations. The following table summarizes the impact of accounts receivable reserves on the gross trade accounts receivable balances as of September 30, 2021 and December 31, 2020: In thousands September 30, 2021 December 31, 2020 Gross trade accounts receivable $ 229,138 $ 203,875 Trade allowances ( 64,857 ) ( 36,242 ) Chargebacks ( 13,975 ) ( 12,114 ) Allowance for doubtful accounts ( 945 ) ( 945 ) Accounts receivable, net $ 149,361 $ 154,574
Inventory	Inventory The Company states inventories at the lower of cost or net realizable value. Cost is determined based on actual cost using the average cost method. Net realizable value is the estimated selling price in the ordinary course of business, less reasonably predictable costs of completion, disposal, and transportation. An allowance is established when management determines that certain inventories may not be saleable. If inventory cost exceeds expected net realizable value due to obsolescence, damage or quantities in excess of expected demand, changes in price levels or other causes, the Company will reduce the carrying value of such inventory to net realizable value and recognize the difference as a component of cost of goods sold in the period in which it occurs. The Company capitalizes inventory purchases of saleable product from approved suppliers while inventory purchases from suppliers prior to regulatory approval are included as a component of research and development expense. The Company expenses inventory identified for use as marketing samples when they are packaged. The average cost reflects the actual purchase price of VASCEPA active pharmaceutical ingredient, or API.
Income Taxes	Income Taxes Deferred tax assets and liabilities are recognized for the future tax consequences of differences between the carrying amounts and tax bases of assets and liabilities and operating loss carryforwards and other tax attributes using enacted rates expected to be in effect when those differences reverse. Valuation allowances are provided against deferred tax assets that are not more likely than not to be realized. Deferred tax assets and liabilities are classified as non-current in the condensed consolidated balance sheet. The Company provides reserves for potential payments of tax to various tax authorities and does not recognize tax benefits related to uncertain tax positions and other issues. Tax benefits for uncertain tax positions are based on a determination of whether a tax benefit taken by the Company in its tax filings or positions is more likely than not to be realized, assuming that the matter in question will be decided based on its technical merits. The Company’s policy is to record interest and penalties in the provision for income taxes, as applicable. The Company regularly assesses its ability to realize deferred tax assets. Changes in historical earnings performance, future earnings projections, and changes in tax laws, among other factors, may cause the Company to adjust its valuation allowance on deferred tax assets, which would impact the Company’s income tax expense in the period in which it is determined that these factors have changed. Excess tax benefits and deficiencies that arise upon vesting or exercise of share-based payments are recognized as an income tax benefit and expense, respectively, in the condensed consolidated statement of operations. Excess income tax benefits are classified as cash flows from operating activities and cash paid to taxing authorities arising from the withholding of shares from employees are classified as cash flows from financing activities. The Company’s and its subsidiaries’ income tax returns are periodically examined by various tax authorities, including the Internal Revenue Service, or IRS, and states. The Company is currently under audit by the IRS for the Company’s 2018 U.S. income tax return and by the New Jersey Department of Treasury for the years 2012 to 2015 and the New York State Department of Taxation and Finance for the years 2017 and 2018 . Although the outcome of tax audits is always uncertain and could result in significant cash tax payments, the Company does not believe the outcome of these audits will have a material adverse effect on its consolidated financial position or results of operations.
Loss per Share	Loss per Share Basic net loss per share is determined by dividing net loss by the weighted average shares of common stock outstanding during the period. Diluted net loss per share is determined by dividing net loss by diluted weighted average shares outstanding. Diluted weighted average shares reflects the dilutive effect, if any, of potentially dilutive common shares, such as common stock options calculated using the treasury stock method and preferred stock using the “if-converted” method. In periods with reported net operating losses, all common stock options and preferred stock outstanding are deemed anti-dilutive such that basic and diluted net loss per share are equal. The Company’s preferred stock, of which none is outstanding as of September 30, 2021 and December 31, 2020, was entitled to receive dividends on an as-if-converted basis in the same form as dividends actually paid on common shares. Accordingly, the preferred stock was considered a participating security and the Company was required to apply the two-class method to consider the impact of the preferred stock on the calculation of basic and diluted earnings per share. The Company is in a net loss position for all of the periods presented and is therefore not required to present the two-class method. The calculation of net loss and the number of shares used to compute basic and diluted net loss per share for the three and nine months ended September 30, 2021 and 2020 are as follows: For the Three Months Ended September 30, For the Nine Months Ended September 30, In thousands 2021 2020 2021 2020 Net loss—basic and diluted $ ( 13,151 ) $ ( 6,788 ) $ ( 6,969 ) $ ( 22,926 ) Weighted average shares outstanding—basic and diluted 396,618 389,699 395,681 378,770 Net loss per share—basic and diluted $ ( 0.03 ) $ ( 0.02 ) $ ( 0.02 ) $ ( 0.06 ) For the three and nine months ended September 30, 2021 and 2020, the following potentially dilutive securities were not included in the computation of net loss per share because the effect would be anti-dilutive or because performance criteria were not yet met for awards contingent upon such measures: For the Three Months Ended September 30, For the Nine Months Ended September 30, In thousands 2021 2020 2021 2020 Stock options 19,146 17,479 19,146 17,479 Restricted stock and restricted stock units 10,307 7,727 10,307 7,727 Preferred stock (if converted) — 2,385 — 2,385 Stock options are anti-dilutive during periods of net earnings when the exercise price of the stock options exceeds the market price of the underlying shares on the last day of the reporting period. Restricted stock and restricted stock units are anti-dilutive during periods of net earnings when underlying performance-based vesting requirements were not achieved as of the last day of the reporting period.
Concentration of Credit Risk	Concentration of Credit Risk Financial instruments that potentially subject the Company to credit risk consist primarily of cash and cash equivalents, short-term and long-term investments, and accounts receivable. The Company maintains substantially all of its cash and cash equivalents and short-term and long-term investments, in financial institutions believed to be of high-credit quality. A significant portion of the Company’s sales are to wholesalers in the pharmaceutical industry. The Company monitors the creditworthiness of customers to whom it grants credit terms and has not experienced any credit losses. The Company does not require collateral or any other security to support credit sales. Three customers individually accounted for 10% or more of the Company’s gross product sales, Customers A, B, and C accounted for 27 % , 37 % , and 28 % , respectively, of gross product sales for the nine months ended September 30, 2021, and represented 34 % , 37 % , and 21 % , respectively, of the gross accounts receivable balance as of September 30, 2021. Customers A, B, and C accounted for 25 % , 37 % , and 30 % , respectively, of gross product sales for the nine months ended September 30, 2020 and represented 37 % , 32 % , and 25 % , respectively, of the gross accounts receivable balance as of September 30, 2020 . The Company has not experienced any significant write-offs of its accounts receivable. All customer accounts are actively managed and no losses in excess of amounts reserved are currently expected; however, the Company is monitoring the potential negative impact of COVID-19 on the Company’s customers’ ability to meet their financial obligations.
Concentration of Suppliers	Concentration of Suppliers The Company has contractual freedom to source the API for VASCEPA and to procure other services supporting its supply chain and has entered into supply agreements with multiple suppliers. The Company’s supply of product for commercial sale and clinical trials is dependent upon relationships with third-party manufacturers and suppliers. The Company cannot provide assurance that its efforts to procure uninterrupted supply of VASCEPA to meet market demand will continue to be successful or that it will be able to renew current supply agreements on favorable terms or at all. Significant alteration to or disruption or termination of the Company’s current supply chain, including as a result of COVID-19, or the Company’s failure to enter into new and similar agreements in a timely fashion, if needed, could have a material adverse effect on its business, condition (financial and other), prospects or results of operations. The Company currently has manufacturing agreements with multiple independent API manufacturers and several independent API encapsulators and packagers for VASCEPA manufacturing. Each of these API manufacturers, encapsulators and packagers is U.S. FDA-approved and certain of these API manufacturers, encapsulators and packagers are also approved for the European Regulatory Authorities for the VAZKEPA manufacturing in Europe, with plans to expand such qualification in Europe to others of these suppliers. These suppliers are also used by the Company to source supply to meet the clinical trial and commercial demands of its partners in other countries. Each of these companies has qualified and validated its manufacturing processes. There can be no guarantee that these or other suppliers with which the Company may contract in the future to manufacture VASCEPA or VASCEPA API will remain qualified to do so to its specifications or that these and any future suppliers will have the manufacturing capacity to meet potential global demand for VASCEPA.
Fair Value of Financial Instruments	Fair Value of Financial Instruments The Company provides disclosure of financial assets and financial liabilities that are carried at fair value based on the price that would be received upon sale of an asset or paid to transfer a liability in an orderly transaction between market participants at the measurement date. Fair value measurements may be classified based on the amount of subjectivity associated with the inputs to fair valuation of these assets and liabilities using the following three levels: Level 1—Inputs are unadjusted quoted prices in active markets for identical assets or liabilities that the Company has the ability to access at the measurement date. Level 2—Inputs include quoted prices for similar assets and liabilities in active markets, quoted prices for identical or similar assets or liabilities in markets that are not active, inputs other than quoted prices that are observable for the asset or liability (i.e., interest rates, yield curves, etc.) and inputs that are derived principally from or corroborated by observable market data by correlation or other means (market corroborated inputs). Level 3—Unobservable inputs that reflect the Company’s estimates of the assumptions that market participants would use in pricing the asset or liability. The Company develops these inputs based on the best information available, including its own data. The following tables present information about the estimated fair value of the Company’s assets and liabilities as of September 30, 2021 and December 31, 2020 and indicate the fair value hierarchy of the valuation techniques the Company utilized to determine such fair value: September 30, 2021 In thousands Total Level 1 Level 2 Level 3 Asset: Money Market Fund $ 116,456 $ 116,456 $ — $ — U.S. Treasury Shares 22,214 22,214 — — Corporate Bonds 95,771 — 95,771 — Commercial Paper 126,832 — 126,832 — Agency Securities 6,748 — 6,748 — Repo Securities 9,000 — 9,000 — Asset Backed Securities 9,895 — 9,895 — Certificate of Deposit 21,575 — 21,575 — Non-US Government 11,523 — 11,523 — Total $ 420,014 $ 138,670 $ 281,344 $ — December 31, 2020 In thousands Total Level 1 Level 2 Level 3 Asset: Money Market Fund $ 88,266 $ 88,266 $ — $ — U.S. Treasury Shares 48,356 48,356 — — Corporate Bonds 179,864 — 179,864 — Commercial Paper 106,650 — 106,650 — Agency Securities 20,782 — 20,782 — Repo Securities 10,000 — 10,000 — Asset Backed Securities 8,599 — 8,599 — Certificate of Deposit 6,125 — 6,125 — Non-US Government 5,240 — 5,240 — Total $ 473,882 $ 136,622 $ 337,260 $ — The carrying amount of the Company’s cash and cash equivalents approximates fair value because of their short-term nature. The cash and cash equivalents consist of cash, deposits with banks and short-term highly liquid money market instruments with remaining maturities at the date of the purchase of 90 days or less. The Company’s held-to-maturity investments are stated at amortized cost, which approximates fair value. The Company does not intend to sell these investment securities and the contractual maturities are not greater than 24 months . Those with maturities greater than 90 days and less than 12 months are included in short-term investments on its condensed consolidated balance sheet. Those with remaining maturities in excess of 12 months are included in long-term investments on its condensed consolidated balance sheet. Unrealized gains or losses on held-to-maturity securities are not recognized until maturity, except other-than-temporary unrealized losses which are recognized in earnings in the period incurred. The Company evaluates securities with unrealized losses to determine whether such losses are other than temporary. The unrealized gain for the nine months ended September 30, 2021 and 2020 was $ 0.1 million and $ 0.9 million, respectively. Interest on investments is reported in interest income.
Segment and Geographical Information	Segment and Geographical Information Operating segments are defined as components of an enterprise about which separate financial information is available that is evaluated on a regular basis by the chief operating decision-maker, or decision-making group, in deciding how to allocate resources to an individual segment and in assessing performance of the segment. The Company currently operates in one business segment, which is the development and commercialization of VASCEPA. A single management team that reports to the Company’s chief decision-maker, who is the Chief Executive Officer, comprehensively manages the business. Accordingly, the Company does not have separately reportable segments.
Restructuring	Restructuring On September 22, 2021, the Company announced a new Go-to-Market strategy for VASCEPA, or the Plan, which aims to expand healthcare professional engagement through a new omnichannel platform, enhance managed care access and optimize VASCEPA prescriptions for cardiovascular risk reduction. As part of the process, the Company reduced its field force to approximately 300 sales representatives and completed this reduction during the three months ended September 30, 2021. The Company estimates that it will incur approximately $ 14.1 million in charges related to the reduction in force, substantially all of which are cash expenditures for one-time termination benefits and associated costs. During the three and nine months ended September 30, 2021 the Company recognized approximately $ 14.1 million within Restructuring expense in the condensed consolidated statements of operations. The following table shows the change in restructuring liability, associated with the Plan, which is included within accrued expenses and other current liabilities: In thousands Restructuring Liability Balance at December 31, 2020 $ — Costs incurred 14,115 Payments — Other (1) ( 306 ) Balance at September 30, 2021 $ 13,809 (1) - Represents the acceleration of expense associated with the vesting of certain equity awards.
Recent Accounting Pronouncements	Recent Accounting Pronouncements From time to time, new accounting pronouncements are issued by the Financial Accounting Standards Board, or FASB, and are early adopted by the Company or adopted as of the specified effective date. In December 2019, the FASB issued ASU No. 2019-12 , Income Taxes (Topic 740), Simplifying the Accounting for Income Taxes, which simplifies the accounting for income taxes by eliminating certain exceptions to the guidance in ASC 740 related to the approach for intraperiod tax allocation, the methodology for calculating income taxes in an interim period, the recognition of deferred tax liabilities for outside basis differences, among other simplifications. The Company adopted this standard effective January 1, 2021 , which did not have an impact on the Company’s condensed consolidated financial statements. The Company believes that the impact of other recently issued but not yet adopted accounting pronouncements will not have a material impact on the Company’s condensed consolidated financial position, results of operations, and cash flows, or do not apply to the Company’s operations.

Significant Accounting Polici_3

Significant Accounting Policies (Tables)	9 Months Ended
	Sep. 30, 2021
Accounting Policies [Abstract]
Summary of Impact of Accounts Receivable Reserves on Gross Trade Accounts Receivable Balances	The following table summarizes the impact of accounts receivable reserves on the gross trade accounts receivable balances as of September 30, 2021 and December 31, 2020: In thousands September 30, 2021 December 31, 2020 Gross trade accounts receivable $ 229,138 $ 203,875 Trade allowances ( 64,857 ) ( 36,242 ) Chargebacks ( 13,975 ) ( 12,114 ) Allowance for doubtful accounts ( 945 ) ( 945 ) Accounts receivable, net $ 149,361 $ 154,574
Calculation of Net Loss and Number of Shares Used to Compute Basic and Diluted Net Loss per Share	The calculation of net loss and the number of shares used to compute basic and diluted net loss per share for the three and nine months ended September 30, 2021 and 2020 are as follows: For the Three Months Ended September 30, For the Nine Months Ended September 30, In thousands 2021 2020 2021 2020 Net loss—basic and diluted $ ( 13,151 ) $ ( 6,788 ) $ ( 6,969 ) $ ( 22,926 ) Weighted average shares outstanding—basic and diluted 396,618 389,699 395,681 378,770 Net loss per share—basic and diluted $ ( 0.03 ) $ ( 0.02 ) $ ( 0.02 ) $ ( 0.06 )
Anti-Dilutive Securities Not Included in the Computation of Net Loss per Share	For the three and nine months ended September 30, 2021 and 2020, the following potentially dilutive securities were not included in the computation of net loss per share because the effect would be anti-dilutive or because performance criteria were not yet met for awards contingent upon such measures: For the Three Months Ended September 30, For the Nine Months Ended September 30, In thousands 2021 2020 2021 2020 Stock options 19,146 17,479 19,146 17,479 Restricted stock and restricted stock units 10,307 7,727 10,307 7,727 Preferred stock (if converted) — 2,385 — 2,385
Estimated Fair Value of Assets and Liability	The following tables present information about the estimated fair value of the Company’s assets and liabilities as of September 30, 2021 and December 31, 2020 and indicate the fair value hierarchy of the valuation techniques the Company utilized to determine such fair value: September 30, 2021 In thousands Total Level 1 Level 2 Level 3 Asset: Money Market Fund $ 116,456 $ 116,456 $ — $ — U.S. Treasury Shares 22,214 22,214 — — Corporate Bonds 95,771 — 95,771 — Commercial Paper 126,832 — 126,832 — Agency Securities 6,748 — 6,748 — Repo Securities 9,000 — 9,000 — Asset Backed Securities 9,895 — 9,895 — Certificate of Deposit 21,575 — 21,575 — Non-US Government 11,523 — 11,523 — Total $ 420,014 $ 138,670 $ 281,344 $ — December 31, 2020 In thousands Total Level 1 Level 2 Level 3 Asset: Money Market Fund $ 88,266 $ 88,266 $ — $ — U.S. Treasury Shares 48,356 48,356 — — Corporate Bonds 179,864 — 179,864 — Commercial Paper 106,650 — 106,650 — Agency Securities 20,782 — 20,782 — Repo Securities 10,000 — 10,000 — Asset Backed Securities 8,599 — 8,599 — Certificate of Deposit 6,125 — 6,125 — Non-US Government 5,240 — 5,240 — Total $ 473,882 $ 136,622 $ 337,260 $ —
Change in Restructuring Liability Associated with the Plan	The following table shows the change in restructuring liability, associated with the Plan, which is included within accrued expenses and other current liabilities: In thousands Restructuring Liability Balance at December 31, 2020 $ — Costs incurred 14,115 Payments — Other (1) ( 306 ) Balance at September 30, 2021 $ 13,809 (1) - Represents the acceleration of expense associated with the vesting of certain equity awards.

Intangible Asset (Tables)

Intangible Asset (Tables)	9 Months Ended
	Sep. 30, 2021
Goodwill and Intangible Assets Disclosure [Abstract]
Schedule of Carrying Value of Intangible Asset	The carrying value as of September 30, 2021 and December 31, 2020 is as follows: In thousands September 30, 2021 December 31, 2020 Technology rights $ 32,081 $ 20,081 Accumulated amortization ( 7,898 ) ( 6,264 ) Intangible asset, net $ 24,183 $ 13,817

Inventory (Tables)

Inventory (Tables)	9 Months Ended
	Sep. 30, 2021
Inventory Disclosure [Abstract]
Schedule of Inventory	The Company capitalizes its purchases of saleable inventory of VASCEPA from suppliers that have been qualified by the U.S. FDA. Inventories as of September 30, 2021 and December 31, 2020 consist of the following: In thousands September 30, 2021 December 31, 2020 Raw materials $ 71,838 $ 50,657 Work in process 39,521 30,388 Finished goods 197,909 107,819 Total inventory $ 309,268 $ 188,864

Equity (Tables)

Equity (Tables)	9 Months Ended
	Sep. 30, 2021
Equity [Abstract]
Summarizes the Aggregate Number of Stock Options And Restricted Stock Unit	The following table summarizes the aggregate number of stock options and restricted stock units, or RSUs, outstanding under the Amarin Corporation plc 2020 Stock Incentive Plan, or the 2020 Plan, as of September 30, 2021: September 30, 2021 Outstanding Stock Options 19,145,833 % of Outstanding Shares 5 % Outstanding RSUs 10,307,168 % of Outstanding Shares 2 %
Summary of Euity Awards Activity	The following table represents equity awards activity during the nine months ended September 30, 2021 and 2020: For the Nine Months Ended September 30, 2021 2020 Stock Options Issued 994,921 642,756 Gross Proceeds $ 2,616,050 $ 1,861,000 Common Shares Issued in settlement of RSUs Vested 1,202,590 1,206,494 Shares retained for settlement of employee tax obligations ─ RSUs 454,973 440,573 Common Shares Issued in settlement of Performance-Based RSUs Vested (1) 1,923,316 1,107,660 Shares retained for settlement of employee tax obligations ─ Performance-Based RSUs 816,931 461,820 (1) Performance-based RSUs vested in connection with the achievement of certain regulatory and sales performance conditions associated with the REDUCE-IT clinical trial and subsequent revenue growth. These performance-based RSUs have fully vested as of August 2021.

Revenue Recognition (Tables)

Revenue Recognition (Tables)	9 Months Ended
	Sep. 30, 2021
Revenue from Contract with Customer [Abstract]
Summarize Activity of the Net Product Revenue Allowance and Reserve Categories	The following tables summarize activity in each of the net product revenue allowance and reserve categories described above for the nine months ended September 30, 2021 and 2020: In thousands Trade Rebates, Product Other Total Balance as of December 31, 2020 $ 36,242 $ 141,201 $ 7,797 $ 5,587 $ 190,827 Provision related to current period sales 90,761 497,726 2,647 36,437 627,571 Provision related to prior period sales — ( 854 ) — — ( 854 ) Credits/payments made for current period sales ( 27,635 ) ( 303,029 ) — ( 31,796 ) ( 362,460 ) Credits/payments made for prior period sales ( 34,511 ) ( 131,320 ) ( 958 ) ( 5,589 ) ( 172,378 ) Balance as of September 30, 2021 $ 64,857 $ 203,724 $ 9,486 $ 4,639 $ 282,706 In thousands Trade Rebates, Product Other Total Balance as of December 31, 2019 $ 29,261 $ 90,997 $ 4,579 $ 3,720 $ 128,557 Provision related to current period sales 95,239 437,030 2,534 50,403 585,206 Provision related to prior period sales — ( 3,872 ) — — ( 3,872 ) Credits/payments made for current period sales ( 32,364 ) ( 304,903 ) — ( 46,768 ) ( 384,035 ) Credits/payments made for prior period sales ( 29,067 ) ( 85,731 ) ( 223 ) ( 3,721 ) ( 118,742 ) Balance as of September 30, 2020 $ 63,069 $ 133,521 $ 6,890 $ 3,634 $ 207,114

Development, Commercializatio_2

Development, Commercialization and Supply Agreements (Tables)	9 Months Ended
	Sep. 30, 2021
Organization, Consolidation and Presentation of Financial Statements [Abstract]
Changes in Balances of Contract Assets and Liabilities and Revenues Recognized	The following table presents changes in the balances of the Company’s contract assets and liabilities during the nine months ended September 30, 2021 and 2020: In thousands Balance at Additions Deductions Balance at Nine months ended September 30, 2021: Contract assets $ — $ — $ — $ — Contract liabilities: Deferred revenue $ 18,632 $ 92 $ ( 1,592 ) $ 17,132 Nine months ended September 30, 2020: Contract assets $ — $ — $ — $ — Contract liabilities: Deferred revenue $ 20,846 $ 3,750 $ ( 5,691 ) $ 18,905 During the nine months ended September 30, 2021 and 2020, the Company recognized the following revenues as a result of changes in the contract asset and contract liability balances in the respective periods: In thousands Nine months ended September 30, Revenue recognized in the period from: 2021 2020 Amounts included in contract liability at the beginning of the period $ 1,555 $ 3,951 Performance obligations satisfied in previous periods $ 33 $ 1,097

Leases (Tables)

Leases (Tables)	9 Months Ended
	Sep. 30, 2021
Leases [Abstract]
Maturity Analysis of Undiscounted Payments for Operating Lease Liabilities and Reconciliation with Carrying Amount of Lease Liability	The table below depicts a maturity analysis of the Company’s undiscounted payments for its operating lease liabilities and their reconciliation with the carrying amount of lease liability presented in the statement of financial position as of September 30, 2021: Undiscounted Remainder of 2021 $ 405 2022 1,774 2023 1,808 2024 1,842 2025 1,876 2026 and thereafter 9,112 Total undiscounted payments $ 16,817 Discount Adjustments $ ( 6,358 ) Current operating lease liability $ 1,730 Long-term operating lease liability $ 8,729

Nature of Business and Basis _2

Nature of Business and Basis of Presentation - Additional Information (Detail)	9 Months Ended
	Sep. 30, 2021USD ($)Segment	Dec. 31, 2020USD ($)
Organization, Consolidation and Presentation of Financial Statements [Abstract]
Number of operating segments | Segment	1
Total assets	$ 1,035,805,000	$ 966,021,000
Cash and liquid short-term and long-term investments	517,900,000
Total current assets	963,033,000	879,233,000
Cash and cash equivalents	222,875,000	186,964,000
Short-term investments	256,267,000	313,969,000
Accounts receivable, net	149,361,000	154,574,000
Inventory	309,268,000	188,864,000
Long-term investments	38,802,000	$ 62,469,000
Debt outstanding	$ 0

Significant Accounting Polici_4

Significant Accounting Policies - Additional Information (Detail) $ in Thousands	3 Months Ended	9 Months Ended
	Sep. 30, 2021USD ($)CustomerSales	Sep. 30, 2021USD ($)SegmentCustomerSales	Sep. 30, 2020USD ($)	Sep. 22, 2021USD ($)
Significant Accounting Policies [Line Items]
Trade receivables, credit period		30 days
Maturities period		24 months
Unrealized gain (loss) on held-to-maturity securities	$ 100	$ 100	$ 900
Number of operating segments | Segment		1
Number of sales representatives | Sales	300	300
Cash expenditures	$ 13,809	$ 13,809
Restructuring and transformation initiative expense	$ 14,115	$ 14,115
Change in accounting principle, accounting standards update, adopted [true false]	true	true
Change in accounting principle, accounting standards update, adoption date	Jan. 1, 2021	Jan. 1, 2021
Change in accounting principle, accounting standards update, immaterial effect [true false]	true	true
Accounting Standards Update [Extensible List]		us-gaap:AccountingStandardsUpdate201912Member
One-time Termination Benefits | Go-to-Market Strategy
Significant Accounting Policies [Line Items]
Cash expenditures				$ 14,100
Short Term Investments
Significant Accounting Policies [Line Items]
Maturities period		12 months
Long Term Investments
Significant Accounting Policies [Line Items]
Maturities period		12 months
Money Market Instruments
Significant Accounting Policies [Line Items]
Maturities period		90 days
Gross Product Sales | Customer Concentration Risk
Significant Accounting Policies [Line Items]
Number of customers | Customer	3	3
Customer A | Gross Product Sales | Customer Concentration Risk
Significant Accounting Policies [Line Items]
Concentration risk percentage		27.00%	25.00%
Customer A | Accounts Receivable | Customer Concentration Risk
Significant Accounting Policies [Line Items]
Concentration risk percentage		34.00%	37.00%
Customer B | Gross Product Sales | Customer Concentration Risk
Significant Accounting Policies [Line Items]
Concentration risk percentage		37.00%	37.00%
Customer B | Accounts Receivable | Customer Concentration Risk
Significant Accounting Policies [Line Items]
Concentration risk percentage		37.00%	32.00%
Customer C | Gross Product Sales | Customer Concentration Risk
Significant Accounting Policies [Line Items]
Concentration risk percentage		28.00%	30.00%
Customer C | Accounts Receivable | Customer Concentration Risk
Significant Accounting Policies [Line Items]
Concentration risk percentage		21.00%	25.00%
Internal Revenue Service (IRS)
Significant Accounting Policies [Line Items]
Open tax year		2018
Earliest Tax Year | New Jersey Department of Treasury
Significant Accounting Policies [Line Items]
Open tax year		2012
Earliest Tax Year | New York State Department of Taxation and Finance
Significant Accounting Policies [Line Items]
Open tax year		2017
Latest Tax Year | New Jersey Department of Treasury
Significant Accounting Policies [Line Items]
Open tax year		2015
Latest Tax Year | New York State Department of Taxation and Finance
Significant Accounting Policies [Line Items]
Open tax year		2018

Significant Accounting Polici_5

Significant Accounting Policies - Summary of Impact of Accounts Receivable Reserves on Gross Trade Accounts Receivable Balances (Detail) - USD ($) $ in Thousands	Sep. 30, 2021	Dec. 31, 2020
Accounts, Notes, Loans and Financing Receivable [Line Items]
Gross trade accounts receivable	$ 229,138	$ 203,875
Accounts receivable, net	149,361	154,574
Trade Allowances
Accounts, Notes, Loans and Financing Receivable [Line Items]
Valuation allowances and reserves	(64,857)	(36,242)
Chargebacks
Accounts, Notes, Loans and Financing Receivable [Line Items]
Valuation allowances and reserves	(13,975)	(12,114)
Allowance for Doubtful Accounts
Accounts, Notes, Loans and Financing Receivable [Line Items]
Valuation allowances and reserves	$ (945)	$ (945)

Significant Accounting Polici_6

Significant Accounting Policies - Calculation of Net Loss and Number of Shares Used to Compute Basic and Diluted Net Loss per Share (Detail) - USD ($) $ / shares in Units, $ in Thousands	3 Months Ended		9 Months Ended
	Sep. 30, 2021	Sep. 30, 2020	Sep. 30, 2021	Sep. 30, 2020
Earnings Loss Per Share [Line Items]
Net loss-basic and diluted	$ (13,151)	$ (6,788)	$ (6,969)	$ (22,926)
Weighted average shares outstanding-basic and diluted	396,618	389,699	395,681	378,770
Net loss per share-basic and diluted	$ (0.03)	$ (0.02)	$ (0.02)	$ (0.06)

Significant Accounting Polici_7

Significant Accounting Policies - Anti-Dilutive Securities Not Included in the Computation of Net Loss per Share (Detail) - shares shares in Thousands	3 Months Ended		9 Months Ended
	Sep. 30, 2021	Sep. 30, 2020	Sep. 30, 2021	Sep. 30, 2020
Preferred Stock
Antidilutive Securities Excluded from Computation of Earnings Per Share [Line Items]
Anti-dilutive securities		2,385		2,385
Stock Options
Antidilutive Securities Excluded from Computation of Earnings Per Share [Line Items]
Anti-dilutive securities	19,146	17,479	19,146	17,479
Restricted Stock and Restricted Stock Units
Antidilutive Securities Excluded from Computation of Earnings Per Share [Line Items]
Anti-dilutive securities	10,307	7,727	10,307	7,727

Significant Accounting Polici_8

Significant Accounting Policies - Estimated Fair Value of Assets and Liability (Detail) - Fair Value, Measurements, Recurring - USD ($) $ in Thousands	Sep. 30, 2021	Dec. 31, 2020
Asset:
Asset, fair value	$ 420,014	$ 473,882
Money Market Fund
Asset:
Asset, fair value	116,456	88,266
U.S. Treasury Shares
Asset:
Asset, fair value	22,214	48,356
Corporate Bonds
Asset:
Asset, fair value	95,771	179,864
Commercial Paper
Asset:
Asset, fair value	126,832	106,650
Agency Securities
Asset:
Asset, fair value	6,748	20,782
Repo Securities
Asset:
Asset, fair value	9,000	10,000
Asset Backed Securities
Asset:
Asset, fair value	9,895	8,599
Certificates of Deposit
Asset:
Asset, fair value	21,575	6,125
Non-US Government
Asset:
Asset, fair value	11,523	5,240
Level 1
Asset:
Asset, fair value	138,670	136,622
Level 1 | Money Market Fund
Asset:
Asset, fair value	116,456	88,266
Level 1 | U.S. Treasury Shares
Asset:
Asset, fair value	22,214	48,356
Level 2
Asset:
Asset, fair value	281,344	337,260
Level 2 | Corporate Bonds
Asset:
Asset, fair value	95,771	179,864
Level 2 | Commercial Paper
Asset:
Asset, fair value	126,832	106,650
Level 2 | Agency Securities
Asset:
Asset, fair value	6,748	20,782
Level 2 | Repo Securities
Asset:
Asset, fair value	9,000	10,000
Level 2 | Asset Backed Securities
Asset:
Asset, fair value	9,895	8,599
Level 2 | Certificates of Deposit
Asset:
Asset, fair value	21,575	6,125
Level 2 | Non-US Government
Asset:
Asset, fair value	$ 11,523	$ 5,240

Significant Accounting Polici_9

Significant Accounting Policies - Change in Restructuring Liability Associated with the Plan (Details) - USD ($) $ in Thousands		3 Months Ended	9 Months Ended
		Sep. 30, 2021	Sep. 30, 2021
Restructuring Reserve [Roll Forward]
Cost incurred		$ 14,115	$ 14,115
Other	[1]		(306)
Balance at September 30, 2021		$ 13,809	$ 13,809
[1]	Represents the acceleration of expense associated with the vesting of certain equity awards.

Intangible Asset - Additional I

Intangible Asset - Additional Information (Detail) £ in Millions, $ in Millions	1 Months Ended	9 Months Ended
	Mar. 31, 2021USD ($)	Sep. 30, 2021	Mar. 31, 2021GBP (£)
Finite-Lived Intangible Assets [Line Items]
Intangible asset estimated weighted- average remaining life		9 years 6 months
Food and Drug Administration
Finite-Lived Intangible Assets [Line Items]
Milestone payment achieved | £			£ 7.5
Increase in intangible assets | $	$ 12

Intangible Asset - Schedule of

Intangible Asset - Schedule of Carrying Value of Intangible Asset (Detail) - USD ($) $ in Thousands	Sep. 30, 2021	Dec. 31, 2020
Goodwill and Intangible Assets Disclosure [Abstract]
Technology rights	$ 32,081	$ 20,081
Accumulated amortization	(7,898)	(6,264)
Intangible asset, net	$ 24,183	$ 13,817

Inventory - Schedule of Invento

Inventory - Schedule of Inventory (Detail) - USD ($) $ in Thousands	Sep. 30, 2021	Dec. 31, 2020
Inventory Disclosure [Abstract]
Raw materials	$ 71,838	$ 50,657
Work in process	39,521	30,388
Finished goods	197,909	107,819
Total inventory	$ 309,268	$ 188,864

Commitments and Contingencies -

Commitments and Contingencies - Additional Information (Detail) $ in Thousands	Sep. 30, 2021USD ($)	Sep. 30, 2021GBP (£)	Dec. 31, 2020USD ($)
Commitments And Contingencies Disclosure [Line Items]
Potential payable amount over the agreement terms based on minimum purchase obligation	$ 213,000
Accrued expenses and other current liabilities	289,684		$ 198,641
Further Indication for AMR101 | Marketing Approval In Europe
Commitments And Contingencies Disclosure [Line Items]
Potential aggregate stock or cash payment | £		£ 7,500,000
Accrued expenses and other current liabilities	12,000
Further Indication for AMR101 | Potential Marketing Approval 1
Commitments And Contingencies Disclosure [Line Items]
Aggregate stock or cash payment upon potential market approval	6,700	5,000,000
Further Indication for AMR101 | Potential Marketing Approval 2
Commitments And Contingencies Disclosure [Line Items]
Aggregate stock or cash payment upon potential market approval	$ 6,700	£ 5,000,000

Equity - Preferred Stock - Addi

Equity - Preferred Stock - Additional Information (Detail)	Mar. 05, 2015USD ($)shares	Mar. 31, 2015USD ($)	Sep. 30, 2021£ / sharesshares	Dec. 31, 2020£ / sharesshares	Dec. 31, 2018shares	Dec. 31, 2015shares	Mar. 05, 2015£ / shares	Mar. 05, 2015$ / shares
Stockholders Equity Note [Line Items]
Preferred stock, par value | £ / shares							£ 0.05
Estimated offering expense | $		$ 700,000
Common stock, par value | £ / shares			£ 0.50	£ 0.50			£ 0.50
Series A Preferred Stock
Stockholders Equity Note [Line Items]
American depositary shares conversion rate to preference shares			American Depositary Shares, or ADSs, each representing one share of Amarin’s Series A Convertible Preference Shares
Ordinary Shares
Stockholders Equity Note [Line Items]
Convertible senior notes, total ADS into which the debt is exchangeable				28,931,746	3,886,718	6,283,333
Preferred stock, equivalent ordinary shares upon future consolidation outstanding			0	0
American Depositary Shares | Series A Preferred Stock
Stockholders Equity Note [Line Items]
Issuance of stock (shares)	391,017,970
Stock issued under private placement, value | $	$ 58,600,000
Preferred Shares Basis
Stockholders Equity Note [Line Items]
Share conversion price | $ / shares								$ 0.15
Ordinary Shares Basis
Stockholders Equity Note [Line Items]
Share conversion price | $ / shares								$ 1.50

Equity - Common Stock - Additio

Equity - Common Stock - Additional Information (Detail) - shares	9 Months Ended
	Sep. 30, 2021	Sep. 30, 2020
Amarin Corporation Plc 2017 Employee Stock Purchase Plan | Ordinary Shares
Stockholders Equity Note [Line Items]
Issuance of common stock, net of transaction costs (shares)	226,402	123,608

Equity - Incentive Equity Award

Equity - Incentive Equity Awards - Summarizes the Aggregate Number of Stock Options And Restricted Stock Unit (Details) - Stock Incentive Plan 2020	Sep. 30, 2021shares
Stockholders Equity Note [Line Items]
Outstanding Stock Options	19,145,833
Stock Options
Stockholders Equity Note [Line Items]
% of Outstanding Shares	5.00%
Restricted Stock Units (RSUs)
Stockholders Equity Note [Line Items]
% of Outstanding Shares	2.00%
Outstanding RSUs	10,307,168

Equity - Incentive Equity Awa_2

Equity - Incentive Equity Awards - Summary of Euity Awards Activity (Details) - USD ($)		9 Months Ended
		Sep. 30, 2021	Sep. 30, 2020
Stockholders Equity Note [Line Items]
Stock Options Issued		994,921	642,756
Gross Proceeds		$ 2,616,050	$ 1,861,000
Restricted Stock Units (RSUs)
Stockholders Equity Note [Line Items]
Common Shares Issued in settlement of RSUs and Performance Based RSUs Vested		1,202,590	1,206,494
Shares retained for settlement of employee tax obligations		454,973	440,573
Performance-Based RSUs
Stockholders Equity Note [Line Items]
Common Shares Issued in settlement of RSUs and Performance Based RSUs Vested	[1]	1,923,316	1,107,660
Shares retained for settlement of employee tax obligations		816,931	461,820
[1]	Performance-based RSUs vested in connection with the achievement of certain regulatory and sales performance conditions associated with the REDUCE-IT clinical trial and subsequent revenue growth. These performance-based RSUs have fully vested as of August 2021.

Equity - Incentive Equity Awa_3

Equity - Incentive Equity Awards - Additional Information (Detail) - USD ($) $ in Thousands		Jun. 14, 2021	Jan. 04, 2021	Jun. 01, 2020	Mar. 02, 2020	Feb. 03, 2020	Sep. 30, 2021	Sep. 30, 2020
Stockholders Equity Note [Line Items]
Stock Options Issued							994,921	642,756
Proceeds from exercise of stock options, net of transaction costs							$ 2,615	$ 1,861
Stock Incentive Plan 2020
Stockholders Equity Note [Line Items]
Stock options, outstanding							19,145,833
Restricted Stock Units (RSUs)
Stockholders Equity Note [Line Items]
Shares issued, related to the vesting of RSUs							1,202,590	1,206,494
Treasury shares for settlement of employee tax obligations							454,973	440,573
Restricted Stock Units (RSUs) | Stock Incentive Plan 2020
Stockholders Equity Note [Line Items]
Restricted stock units, outstanding							10,307,168
Percentage of outstanding shares on a fully diluted basis							2.00%
Stock units, Granted		218,000	3,265,700
Stock units, Vesting Period		3 years	3 years
Restricted Stock Units (RSUs) | Stock Incentive Plan 2011
Stockholders Equity Note [Line Items]
Stock units, Granted				782,520	821,950
Restricted Stock Units (RSUs) | Employees | Stock Incentive Plan 2020
Stockholders Equity Note [Line Items]
Stock units, Granted			1,345,800
Restricted Stock Units (RSUs) | Employees | Stock Incentive Plan 2011
Stockholders Equity Note [Line Items]
Stock units, Granted						1,253,400
Stock units, Vesting Period					3 years
Stock Options | Stock Incentive Plan 2020
Stockholders Equity Note [Line Items]
Percentage of outstanding shares on a fully diluted basis							5.00%
Stock options, Granted		278,271	3,100,200
Stock units, Vesting Period			4 years
Stock units, Cliff Vesting Period			1 year
Stock Options | Stock Incentive Plan 2011
Stockholders Equity Note [Line Items]
Stock options, Granted						1,875,000
Stock Options | Employees | Stock Incentive Plan 2011
Stockholders Equity Note [Line Items]
Stock units, Vesting Period						4 years
Performance-Based RSUs
Stockholders Equity Note [Line Items]
Shares issued, related to the vesting of RSUs	[1]						1,923,316	1,107,660
Treasury shares for settlement of employee tax obligations							816,931	461,820
[1]	Performance-based RSUs vested in connection with the achievement of certain regulatory and sales performance conditions associated with the REDUCE-IT clinical trial and subsequent revenue growth. These performance-based RSUs have fully vested as of August 2021.

Co-Promotion Agreement - Additi

Co-Promotion Agreement - Additional Information (Detail) - USD ($) $ in Thousands	9 Months Ended	12 Months Ended
	Sep. 30, 2021	Dec. 31, 2018	Dec. 31, 2020
Co Promotion Agreement [Line Items]
Accrued expenses and other current liabilities	$ 289,684		$ 198,641
Co-Promotion Agreement | Kowa Pharmaceuticals America, Inc.
Co Promotion Agreement [Line Items]
Promotion fee as a percentage of gross margin		18.50%
Maximum co-promotion tail payments receive period	3 years
Co-promotion tail payments payable		$ 17,800
Accrued co- promotion tail payments		$ 16,600
Accrued expenses and other liabilities	$ 1,300		3,800
Accrued expenses and other current liabilities			$ 3,200

Revenue Recognition - Additiona

Revenue Recognition - Additional Information (Detail)	9 Months Ended
	Sep. 30, 2021
Disaggregation Of Revenue [Line Items]
Payment period from distributors received from date of sale	30 days
Effect of significant financing component when transfer and customer payment of good or service occurs within one year or less	true
VASCEPA 1-Gram
Disaggregation Of Revenue [Line Items]
Product expiration date after being converted into capsule form	4 years
VASCEPA 0.5-Gram
Disaggregation Of Revenue [Line Items]
Product expiration date after being converted into capsule form	3 years
Minimum
Disaggregation Of Revenue [Line Items]
Payment period from distributors received from date of sale	30 days
Minimum | U.S. and Germany
Disaggregation Of Revenue [Line Items]
Sales discount percentage	2.00%
Maximum
Disaggregation Of Revenue [Line Items]
Payment period from distributors received from date of sale	60 days
Maximum | U.S. and Germany
Disaggregation Of Revenue [Line Items]
Sales discount percentage	3.00%

Revenue Recognition - Summarize

Revenue Recognition - Summarize Activity of the Net Product Revenue Allowance and Reserve Categories (Detail) - USD ($) $ in Thousands	9 Months Ended
	Sep. 30, 2021	Sep. 30, 2020
Valuation And Qualifying Accounts Disclosure [Line Items]
Beginning balance	$ 190,827	$ 128,557
Provision related to current period sales	627,571	585,206
Provision related to prior period sales	(854)	(3,872)
Credits/payments made for current period sales	(362,460)	(384,035)
Credits/payments made for prior period sales	(172,378)	(118,742)
Ending balance	282,706	207,114
Trade Allowances
Valuation And Qualifying Accounts Disclosure [Line Items]
Beginning balance	36,242	29,261
Provision related to current period sales	90,761	95,239
Credits/payments made for current period sales	(27,635)	(32,364)
Credits/payments made for prior period sales	(34,511)	(29,067)
Ending balance	64,857	63,069
Rebates, Chargebacks and Discounts
Valuation And Qualifying Accounts Disclosure [Line Items]
Beginning balance	141,201	90,997
Provision related to current period sales	497,726	437,030
Provision related to prior period sales	(854)	(3,872)
Credits/payments made for current period sales	(303,029)	(304,903)
Credits/payments made for prior period sales	(131,320)	(85,731)
Ending balance	203,724	133,521
Product Returns
Valuation And Qualifying Accounts Disclosure [Line Items]
Beginning balance	7,797	4,579
Provision related to current period sales	2,647	2,534
Credits/payments made for prior period sales	(958)	(223)
Ending balance	9,486	6,890
Other Incentives
Valuation And Qualifying Accounts Disclosure [Line Items]
Beginning balance	5,587	3,720
Provision related to current period sales	36,437	50,403
Credits/payments made for current period sales	(31,796)	(46,768)
Credits/payments made for prior period sales	(5,589)	(3,721)
Ending balance	$ 4,639	$ 3,634

Development, Commercializatio_3

Development, Commercialization and Supply Agreement - Additional Information (Detail)	1 Months Ended							3 Months Ended		9 Months Ended		12 Months Ended
	Jan. 31, 2021USD ($)	Feb. 29, 2020USD ($)	Jan. 31, 2020USD ($)	Sep. 30, 2018USD ($)	Sep. 30, 2017USD ($)	Mar. 31, 2016USD ($)	Feb. 28, 2015USD ($)	Sep. 30, 2021USD ($)	Sep. 30, 2020USD ($)	Sep. 30, 2021USD ($)Item	Sep. 30, 2020USD ($)	Dec. 31, 2020USD ($)	Dec. 31, 2018USD ($)	Dec. 31, 2019USD ($)
License And Collaboration Agreements [Line Items]
Revenue recognized related to upfront and milestone payments										$ 1,592,000	$ 5,691,000
Licenses revenue								$ 142,038,000	$ 156,499,000	438,696,000	446,809,000
Deferred revenue								17,132,000	18,905,000	17,132,000	18,905,000	$ 18,632,000		$ 20,846,000
Product Revenue, Net
License And Collaboration Agreements [Line Items]
Licenses revenue								141,442,000	155,190,000	$ 436,598,000	441,118,000
Mochida Pharmaceutical Co., Ltd. | In-licenses
License And Collaboration Agreements [Line Items]
Milestones payment	$ 1,000,000											1,000,000
Mochida Pharmaceutical Co., Ltd. | In-licenses | Research and Development Expense
License And Collaboration Agreements [Line Items]
Upfront payment													$ 2,700,000
Edding | Out-licenses
License And Collaboration Agreements [Line Items]
Non-refundable up-front received							$ 15,000,000
Number of indications of the regulatory milestone events relating to the submission and approval | Item										3
Amounts to be received upon achievement of the regulatory milestone events								33,000,000		$ 33,000,000
Sales-based milestone event payment								120,000,000		120,000,000
Revenue recognized related to upfront and milestone payments										800,000	2,200,000
Deferred revenue								10,000,000		10,000,000		10,800,000
Edding | Out-licenses | Licensing Revenue
License And Collaboration Agreements [Line Items]
Licenses revenue										6,900,000		6,100,000
Edding | Out-licenses | Maximum
License And Collaboration Agreements [Line Items]
Additional upfront payment eligible to receive based on development, regulatory and sales Milestone								153,000,000		153,000,000
Amounts to be received upon achievement of the regulatory milestone events								15,000,000		15,000,000
Sales-based milestone event payment								50,000,000		50,000,000
Edding | Out-licenses | Minimum
License And Collaboration Agreements [Line Items]
Amounts to be received upon achievement of the regulatory milestone events								2,000,000		2,000,000
Sales-based milestone event payment								5,000,000		5,000,000
Edding | Out-licenses | Clinical Trial Application
License And Collaboration Agreements [Line Items]
Non-refundable milestone payment received						$ 1,000,000
Biologix FZCo | Out-licenses
License And Collaboration Agreements [Line Items]
Revenue recognition period of non-refundable up-front payment						10 years
Biologix FZCo | Out-licenses | Product Revenue, Net
License And Collaboration Agreements [Line Items]
Licenses revenue								500,000	500,000	1,000,000	500,000
HLS | Out-licenses
License And Collaboration Agreements [Line Items]
Non-refundable up-front received					$ 5,000,000
Non-refundable milestone payment received		$ 2,500,000	$ 3,800,000	$ 2,500,000	$ 2,500,000
Revenue recognized related to upfront and milestone payments										700,000	3,500,000
Deferred revenue								6,400,000		6,400,000		7,100,000
Non-refundable up-front received period					6 months
Non-refundable milestone payment received					$ 3,800,000
HLS | Out-licenses | Health Canada
License And Collaboration Agreements [Line Items]
Non-refundable milestone payment received					2,500,000
HLS | Out-licenses | Licensing Revenue
License And Collaboration Agreements [Line Items]
Licenses revenue										7,300,000		$ 6,600,000
HLS | Out-licenses | Product Revenue, Net
License And Collaboration Agreements [Line Items]
Licenses revenue											$ 8,500,000
HLS | Out-licenses | Maximum
License And Collaboration Agreements [Line Items]
Additional upfront payment eligible to receive based on development, regulatory and sales Milestone					$ 50,000,000

Development, Commercializatio_4

Development, Commercialization and Supply Agreement - Additional Information (Detail 1) - Out-licenses - Revenue, Remaining Performance Obligation, Expected Timing of Satisfaction, Start Date: 2021-10-01	Sep. 30, 2021
Edding
License And Collaboration Agreements [Line Items]
Revenue recognized over remaining period	13 years
HLS
License And Collaboration Agreements [Line Items]
Revenue recognized over remaining period	9 years

Development, Commercializatio_5

Development, Commercialization and Supply Agreement - Changes in Balances of Contract Assets and Liabilities (Detail) - USD ($) $ in Thousands	9 Months Ended
	Sep. 30, 2021	Sep. 30, 2020
Contract liabilities:
Deferred revenue, Balance at Beginning of Period	$ 18,632	$ 20,846
Deferred revenue, Additions	92	3,750
Deferred revenue, Deductions	(1,592)	(5,691)
Deferred revenue, Balance at End of Period	$ 17,132	$ 18,905

Development, Commercializatio_6

Development, Commercialization and Supply Agreement - Recognized Revenues Changes in Contract Asset and Contract Liability Balances (Detail) - USD ($) $ in Thousands	9 Months Ended
	Sep. 30, 2021	Sep. 30, 2020
Revenue recognized in the period from:
Amounts included in contract liability at the beginning of the period	$ 1,555	$ 3,951
Performance obligations satisfied in previous periods	$ 33	$ 1,097

Leases - Additional Information

Leases - Additional Information (Detail) $ in Thousands	Aug. 15, 2019USD ($)RenewalOption	Sep. 30, 2021USD ($)	Sep. 30, 2020USD ($)	Sep. 30, 2021USD ($)	Sep. 30, 2020USD ($)	Dec. 31, 2020USD ($)
Lessee Lease Description [Line Items]
Incremental borrowing rate for purposes of calculation of lease liabilities		11.50%		11.50%
Change in incremental borrowing rate				1.00%
Monthly rent payment		$ 16,817		$ 16,817
Operating lease liability		10,500		10,500		$ 10,600
Operating lease right-of-use asset		7,762		7,762		$ 8,054
Operating lease expense		$ 500	$ 400	$ 1,500	$ 1,200
Bridgewater
Lessee Lease Description [Line Items]
Lease commencement date	Aug. 15, 2019
Lease agreement term	11 years
Number of renewal options | RenewalOption	2
Lease renewal term	5 years
Description of lease agreement				Amarin will have a one-time option to terminate the agreement effective on the first day of the 97th month after the Commencement Date upon advance written notice and a termination payment specified in the Lease.
Lease termination description				one-time option to terminate the agreement effective on the first day of the 97th month after the Commencement Date
Lease termination existence of option to extend	true
Monthly rent payment	$ 100
Maximum
Lessee Lease Description [Line Items]
Short term lease period				12 months

Leases - Maturity Analysis of U

Leases - Maturity Analysis of Undiscounted Payments for Operating Lease Liabilities and Reconciliation with Carrying Amount of Lease Liability (Detail) - USD ($) $ in Thousands	Sep. 30, 2021	Dec. 31, 2020
Undiscounted lease payments
Remainder of 2021	$ 405
2022	1,774
2023	1,808
2024	1,842
2025	1,876
2026 and thereafter	9,112
Total undiscounted payments	16,817
Discount Adjustments	(6,358)
Current operating lease liability	$ 1,730
Operating lease, liability, current, statement of financial position [Extensible List]	Accrued expenses and other current liabilities
Long-term operating lease liability	$ 8,729	$ 9,153