COMPASS Pathways (CMPS) 6-K 9 Nov 21 2021 Q3 Current report (foreign) Financial data

Cover

Cover	9 Months Ended
	Sep. 30, 2021
Cover [Abstract]
Document Type	6-K
Entity Registrant Name	COMPASS PATHWAYS PLC
Entity Address, Address Line One	3rd Floor
Entity Address, Address Line Two	1 Ashley Road
Entity Address, City or Town	Altrincham
Entity Address, Postal Zip Code	WA14 2DT
Entity Address, Country	GB
Entity Central Index Key	0001816590
Document Fiscal Year Focus	2021
Document Fiscal Period Focus	Q3
Amendment Flag	false
Current Fiscal Year End Date	--12-31
Document Period End Date	Sep. 30, 2021

Condensed Consolidated Balance

Condensed Consolidated Balance Sheets $ in Thousands	Sep. 30, 2021USD ($)	Dec. 31, 2020USD ($)
CURRENT ASSETS:
Cash and cash equivalents	$ 293,959	$ 190,327
Restricted cash	104	29
Prepaid expenses and other current assets	18,733	12,048
Total current assets	312,796	202,404
Investment	521	529
Property and equipment, net	355	245
Deferred tax assets	852	221
Other assets	219	57
Total assets	314,743	203,456
CURRENT LIABILITIES:
Accounts payable	2,742	2,747
Accrued expenses and other liabilities	6,581	4,148
Total current liabilities	9,323	6,895
Total liabilities	9,323	6,895
Commitments and contingencies (Note 13)
SHAREHOLDERS’ EQUITY:
Additional paid-in capital	441,135	279,480
Accumulated other comprehensive income	7,817	14,585
Accumulated deficit	(143,991)	(97,899)
Total shareholders’ equity	305,420	196,561
Total liabilities and shareholders' equity	314,743	203,456
Ordinary Shares
SHAREHOLDERS’ EQUITY:
Ordinary and deferred shares, value, issued	431	367
Deferred Shares
SHAREHOLDERS’ EQUITY:
Ordinary and deferred shares, value, issued	$ 28	$ 28

Condensed Consolidated Balanc_2

Condensed Consolidated Balance Sheets (Parenthetical) - £ / shares	Sep. 30, 2021	Dec. 31, 2020
Common stock, outstanding (in shares)		35,930,331
Ordinary Shares
Common stock, outstanding (in shares)	41,731,180
Common stock, par value (in dollars per share)	£ 0.008	£ 0.008
Common stock, authorized (in shares)	41,731,180	35,930,331
Common stock, issued (in shares)	41,731,180	35,930,331
Deferred Shares
Common stock, outstanding (in shares)	1	1
Common stock, par value (in dollars per share)	£ 21,921.504	£ 21,921.504
Common stock, authorized (in shares)	1	1
Common stock, issued (in shares)	1	1

Condensed Consolidated Statemen

Condensed Consolidated Statements of Operations and Comprehensive Loss - USD ($) $ in Thousands	3 Months Ended		9 Months Ended
	Sep. 30, 2021	Sep. 30, 2020	Sep. 30, 2021	Sep. 30, 2020
OPERATING EXPENSES:
Research and development	$ 12,197	$ 6,875	$ 30,434	$ 18,822
General and administrative	9,571	6,607	24,464	21,052
Total operating expenses	21,768	13,482	54,898	39,874
LOSS FROM OPERATIONS:	(21,768)	(13,482)	(54,898)	(39,874)
OTHER INCOME (EXPENSE), NET:
Other income, net	0	109	2	302
Foreign exchange gains (losses)	3,364	(4,331)	2,171	(3,252)
Fair value change of convertible notes	0	0	0	(1,031)
Fair value change of convertible notes - due to a related party	0	0	0	(723)
Benefit from R&D tax credit	2,618	1,092	6,733	3,175
Total other income (expense), net	5,982	(3,130)	8,906	(1,529)
Loss before income taxes	(15,786)	(16,612)	(45,992)	(41,403)
Income tax expense	(63)	(82)	(100)	(125)
Net loss attributable to ordinary shareholders - basic	(15,849)	(16,694)	(46,092)	(41,528)
Net loss attributable to ordinary shareholders - diluted	(15,849)	(16,694)	(46,092)	(41,528)
Other comprehensive (loss) income:
Foreign exchange translation adjustment, net of tax	(8,401)	4,806	(6,768)	3,773
Comprehensive loss	$ (24,250)	$ (11,888)	$ (52,860)	$ (37,755)
Net loss per share attributable to ordinary shareholders - basic (in dollars per share)	$ (0.38)	$ (1.30)	$ (1.17)	$ (3.90)
Net loss per share attributable to ordinary shareholders - diluted (in dollars per share)	$ (0.38)	$ (1.30)	$ (1.17)	$ (3.90)
Weighted average ordinary shares outstanding - basic (in shares)	41,708,220	12,834,889	39,378,824	10,638,738
Weighted average ordinary shares outstanding - diluted (in shares)	41,708,220	12,834,889	39,378,824	10,638,738

Condensed Consolidated Statem_2

Condensed Consolidated Statements of Convertible Preferred Shares and Shareholders’ Equity (Deficit) $ in Thousands	USD ($)shares	IPOUSD ($)	Options Granted In Previous YearUSD ($)	Share optionsUSD ($)shares	Convertible A preferred stockUSD ($)shares	Convertible B preferred stockUSD ($)shares	Ordinary Shares£ / sharesshares	Deferred Shares£ / sharesshares	Common StockOrdinary SharesUSD ($)shares	Common StockOrdinary SharesIPOUSD ($)shares	Common StockOrdinary SharesOptions Granted In Previous YearUSD ($)shares	Common StockDeferred SharesUSD ($)shares	ADDITIONAL PAID-IN CAPITALUSD ($)	ADDITIONAL PAID-IN CAPITALIPOUSD ($)	ADDITIONAL PAID-IN CAPITALOptions Granted In Previous YearUSD ($)	ACCUMULATED OTHER COMPREHENSIVE INCOME (LOSS)USD ($)	ACCUMULATED DEFICITUSD ($)
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Common stock, par value (in dollars per share) | £ / shares							£ 0.008	£ 21,921.504
Convertible preferred shares beginning balance (in shares) at Dec. 31, 2019 | shares	9,782,505			2,650,980	7,131,525	0
Convertible preferred shares beginning balance at Dec. 31, 2019	$ 38,908			$ 3,761	$ 35,147	$ 0
Convertible preferred shares ending balance (in shares) at Mar. 31, 2020 | shares				2,650,980	7,131,525	0
Convertible preferred shares ending balance at Mar. 31, 2020				$ 3,761	$ 35,147	$ 0
Beginning balance (in shares) at Dec. 31, 2019 | shares									10,752,429			0
Beginning balance at Dec. 31, 2019	(30,390)								$ 111			$ 0	$ 7,162			$ (98)	$ (37,565)
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Share-based compensation expense	1,704												1,704
Unrealized gain (loss) on foreign currency translation	(348)															(348)
Net loss	(8,585)																(8,585)
Ending balance (in shares) at Mar. 31, 2020 | shares									10,752,429			0
Ending balance at Mar. 31, 2020	$ (37,619)								$ 111			$ 0	8,866			(446)	(46,150)
Convertible preferred shares beginning balance (in shares) at Dec. 31, 2019 | shares	9,782,505			2,650,980	7,131,525	0
Convertible preferred shares beginning balance at Dec. 31, 2019	$ 38,908			$ 3,761	$ 35,147	$ 0
Convertible preferred shares ending balance (in shares) at Sep. 30, 2020 | shares				0	0	0
Convertible preferred shares ending balance at Sep. 30, 2020				$ 0	$ 0	$ 0
Beginning balance (in shares) at Dec. 31, 2019 | shares									10,752,429			0
Beginning balance at Dec. 31, 2019	(30,390)								$ 111			$ 0	7,162			(98)	(37,565)
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Net loss	(41,528)
Ending balance (in shares) at Sep. 30, 2020 | shares									35,930,331			1,000
Ending balance at Sep. 30, 2020	203,075								$ 367			$ 28	278,098			3,675	(79,093)
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Common stock, par value (in dollars per share) | £ / shares							0.008	21,921.504
Convertible preferred shares beginning balance (in shares) at Mar. 31, 2020 | shares				2,650,980	7,131,525	0
Convertible preferred shares beginning balance at Mar. 31, 2020				$ 3,761	$ 35,147	$ 0
Increase (Decrease) in Temporary Equity [Roll Forward]
Issuance of B convertible preferred shares, net of issuance costs (in shares) | shares						4,487,533
Issuance of B convertible preferred shares, net of issuance costs						$ 55,975
Conversion of notes into B convertible preferred shares (in shares) | shares						1,723,263
Conversion of notes into B convertible preferred shares						$ 21,614
Convertible preferred shares ending balance (in shares) at Jun. 30, 2020 | shares				2,650,980	7,131,525	6,210,796
Convertible preferred shares ending balance at Jun. 30, 2020				$ 3,761	$ 35,147	$ 77,589
Beginning balance (in shares) at Mar. 31, 2020 | shares									10,752,429			0
Beginning balance at Mar. 31, 2020	(37,619)								$ 111			$ 0	8,866			(446)	(46,150)
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Share-based compensation expense	9,698												9,698
Unrealized gain (loss) on foreign currency translation	(685)															(685)
Net loss	(16,249)																(16,249)
Ending balance (in shares) at Jun. 30, 2020 | shares									10,752,429			0
Ending balance at Jun. 30, 2020	(44,855)								$ 111			$ 0	18,564			(1,131)	(62,399)
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Common stock, par value (in dollars per share) | £ / shares							0.008	21,921.504
Issuance of B convertible preferred shares, net of issuance costs (in shares) | shares						425,871
Issuance of B convertible preferred shares, net of issuance costs						$ 5,341
Convertible preferred shares ending balance (in shares) at Sep. 30, 2020 | shares				0	0	0
Convertible preferred shares ending balance at Sep. 30, 2020				$ 0	$ 0	$ 0
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Issuance of ordinary shares, net of issuance costs (in shares) | shares										8,625,000
Issuance of ordinary shares, net of issuance costs		$ 132,765								$ 88				$ 132,677
Exercise of share options (in shares) | shares									197,702
Exercise of share options	0								$ 2				(2)
Forfeited (in shares) | shares									(63,972)
Forfeiture of ordinary shares	0								$ (1)				1
Effect of corporate reorganization including conversion of preferred shares to ordinary shares (in shares) | shares				(2,650,980)	(7,131,525)	(6,636,667)			(16,419,172)			(1,000)
Unrealized gain (loss) on foreign currency translation	(121,838)			$ (3,761)	$ (35,147)	$ (82,930)			$ (167)			$ (28)	(121,643)
Share-based compensation expense	5,215												5,215
Unrealized gain (loss) on foreign currency translation	4,806															4,806
Net loss	(16,694)																(16,694)
Ending balance (in shares) at Sep. 30, 2020 | shares									35,930,331			1,000
Ending balance at Sep. 30, 2020	$ 203,075								$ 367			$ 28	278,098			3,675	(79,093)
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Common stock, par value (in dollars per share) | £ / shares							0.008	21,921.504
Common stock, par value (in dollars per share) | £ / shares							£ 0.008	£ 21,921.504
Beginning balance (in shares) at Dec. 31, 2020 | shares	35,930,331							1	35,930,331			1
Beginning balance at Dec. 31, 2020	$ 196,561								$ 367			$ 28	279,480			14,585	(97,899)
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Exercise of share options (in shares) | shares									581,328		232,227
Exercise of share options	998		$ 0						$ 6		$ 3		992		$ (3)
Share-based compensation expense	1,666												1,666
Unrealized gain (loss) on foreign currency translation	1,988															1,988
Net loss	(12,715)																(12,715)
Ending balance (in shares) at Mar. 31, 2021 | shares									36,743,886			1
Ending balance at Mar. 31, 2021	$ 188,498								$ 376			$ 28	282,135			16,573	(110,614)
Convertible preferred shares ending balance (in shares) at Sep. 30, 2021 | shares				0	0	0
Convertible preferred shares ending balance at Sep. 30, 2021				$ 0	$ 0	$ 0
Beginning balance (in shares) at Dec. 31, 2020 | shares	35,930,331							1	35,930,331			1
Beginning balance at Dec. 31, 2020	$ 196,561								$ 367			$ 28	279,480			14,585	(97,899)
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Issuance of ordinary shares, net of issuance costs (in shares) | shares							1,188,242
Exercise of share options (in shares) | shares	1,015,915										59,900
Vested (in shares) | shares	12,607
Net loss	$ (46,092)
Ending balance (in shares) at Sep. 30, 2021 | shares							41,731,180	1	41,731,180			1
Ending balance at Sep. 30, 2021	305,420								$ 431			$ 28	441,135			7,817	(143,991)
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Common stock, par value (in dollars per share) | £ / shares							£ 0.008	£ 21,921.504
Beginning balance (in shares) at Mar. 31, 2021 | shares									36,743,886			1
Beginning balance at Mar. 31, 2021	188,498								$ 376			$ 28	282,135			16,573	(110,614)
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Issuance of ordinary shares, net of issuance costs (in shares) | shares									4,600,000
Issuance of ordinary shares, net of issuance costs	154,794								$ 51				154,743
Exercise of share options (in shares) | shares									351,449		232,227
Exercise of share options	47								$ 4				43
Share-based compensation expense	1,904												1,904
Unrealized gain (loss) on foreign currency translation	(355)															(355)
Net loss	(17,528)																(17,528)
Ending balance (in shares) at Jun. 30, 2021 | shares									41,695,335			1
Ending balance at Jun. 30, 2021	327,360								$ 431			$ 28	438,825			16,218	(128,142)
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Common stock, par value (in dollars per share) | £ / shares							£ 0.008	£ 21,921.504
Convertible preferred shares ending balance (in shares) at Sep. 30, 2021 | shares				0	0	0
Convertible preferred shares ending balance at Sep. 30, 2021				$ 0	$ 0	$ 0
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Exercise of share options (in shares) | shares									23,238
Exercise of share options	23												23
Share-based compensation expense	2,287												2,287
Unrealized gain (loss) on foreign currency translation	(8,401)															(8,401)
Net loss	(15,849)																(15,849)
Ending balance (in shares) at Sep. 30, 2021 | shares							41,731,180	1	41,731,180			1
Ending balance at Sep. 30, 2021	$ 305,420								$ 431			$ 28	$ 441,135			$ 7,817	$ (143,991)
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Common stock, par value (in dollars per share) | £ / shares							£ 0.008	£ 21,921.504

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	$ (46,092)	$ (41,528)
Adjustments to reconcile net loss to net cash used in operating activities
Depreciation and amortization	123	84
Non-cash gain on foreign currency remeasurement	31	0
Change in fair value of convertible notes	0	1,754
Non-cash share-based compensation	5,857	16,617
Changes in operating assets and liabilities
Prepaid expenses and other current assets	(6,798)	(3,685)
Deferred tax assets	(631)	0
Other assets	(168)	(59)
Accounts payable	36	1,338
Accrued expenses and other liabilities	2,266	853
Net cash used in operating activities	(45,376)	(24,626)
CASH FLOWS FROM INVESTING ACTIVITIES:
Purchases of property and equipment	(241)	(104)
Purchase of investments	0	(492)
Net cash used in investing activities	(241)	(596)
CASH FLOWS FROM FINANCING ACTIVITIES:
Proceeds from exercise of options	1,047	0
Proceeds of issuance of preferred shares, net of issuance costs	0	61,316
Proceeds of issuance of ordinary shares, net of issuance costs	154,794	132,823
Net cash provided by financing activities	155,841	194,139
Effect of exchange rate changes on cash, cash equivalents and restricted cash	(6,517)	2,633
Net increase in cash, cash equivalents and restricted cash	103,707	171,550
Cash, cash equivalents and restricted cash, beginning of the period	190,356	24,984
Cash, cash equivalents and restricted cash, end of the period	294,063	196,534
SUPPLEMENTAL DISCLOSURE OF CASH FLOW INFORMATION:
Proceeds from exercise of options which were not received and recorded in other current assets	21	0
Deferred issuance costs included in accrued expenses	234	0
Conversion of convertible notes into convertible preferred shares	0	21,614
Cash, Cash Equivalents, Restricted Cash and Restricted Cash Equivalents [Abstract]
Cash and cash equivalents	293,959	196,505
Restricted cash	104	29
Cash and cash equivalents	$ 294,063	$ 196,534

Condensed Consolidated Statem_4

Condensed Consolidated Statements of Convertible Preferred Shares and Shareholders’ Equity (Deficit) (Parenthetical) $ in Thousands	3 Months Ended
	Sep. 30, 2020USD ($)
IPO
Issuance costs of ordinary shares in initial public offering	$ 4,838

Nature of Business

Nature of Business	9 Months Ended
	Sep. 30, 2021
Organization, Consolidation and Presentation of Financial Statements [Abstract]
Nature of Business	Nature of Business COMPASS Pathways plc, or the Company, is a mental health care company dedicated to accelerating patient access to evidence-based innovation in mental health. The Company is developing psilocybin therapy through late-stage clinical trials in Europe and North America for patients with treatment-resistant depression. The Company is a public limited company incorporated in England and Wales and was originally incorporated under the name COMPASS Rx Limited before being renamed COMPASS Pathways plc as part of our corporate reorganization as more particularly described below. Prior to and in contemplation of the consummation of the Company's initial public offering, or IPO, of American Depositary Shares, or ADSs, the Company undertook a corporate reorganization. The corporate reorganization took place in several steps, all of which have been completed. The Company refers to the following steps, which are discussed in more detail below, as the “corporate reorganization”. • Prior to the corporate reorganization, the holding company of the COMPASS group was COMPASS Pathfinder Holdings Limited. • Pursuant to the terms of a share for share exchange completed on August 7, 2020, all of the shareholders of COMPASS Pathfinder Holdings Limited, which, until the corporate reorganization was the holding company of the COMPASS group, exchanged each of the shares held by them for 1,161 of the same class, with the same shareholder rights, of newly issued shares of COMPASS Rx Limited and, as a result, COMPASS Pathfinder Holdings Limited became a wholly owned subsidiary of COMPASS Rx Limited. This share exchange had the effect of a 1:1,161 share split. No shareholder rights or preferences changed as a result of the share for share exchange. COMPASS Pathfinder Holdings Limited is a private limited liability company incorporated under the laws of England and Wales and its primary offices are in London, United Kingdom (“UK”). COMPASS Pathfinder Holdings Limited has one wholly-owned subsidiary, COMPASS Pathfinder Limited, whose primary office is in London, United Kingdom. COMPASS Pathfinder Limited has one wholly-owned subsidiary, COMPASS Pathways Inc. whose primary office is located in New York, United States of America. • Pursuant to Part 17 of the Companies Act 2006, on August 19, 2020, COMPASS Rx Limited reduced its share capital by way of a reduction of the nominal value of each share in the capital of COMPASS Rx Limited from £1.00 to £0.001 in order to satisfy the net asset test requirement in section 92 of the Companies Act 2006 for the re-registration of COMPASS Rx Limited as a public limited company and to create distributable reserves in order to support future distribution activities by the Company (although we note that none is currently planned). • COMPASS Rx Limited was re-registered as a public limited company and renamed COMPASS Pathways plc, effective on August 21, 2020. COMPASS Pathways plc is a holding company with nominal activity. • Immediately prior to the completion of the Company’s IPO on September 22, 2020, the different classes of issued share capital of COMPASS Pathways plc were reorganized on a one-for-0.1136 basis into a single class of 27,305,331 ordinary shares by way of a reverse share split, which was retroactively restated in our condensed consolidated financial statements. As part of this reverse share split, the nominal value of COMPASS Pathways plc’s ordinary shares changed from £0.001 per share to £0.008 per share and a single, non-voting deferred share with a nominal value of £21,921.504 in the capital of the Company was created and transferred to the Company. • On September 22, 2020, the Company completed the IPO. In the IPO, the Company sold an aggregate of 8,625,000 ADSs representing the same number of ordinary shares, including 1,125,000 ADSs pursuant to the underwriters’ over-allotment right option to purchase additional ADSs, at a public offering price of $17.00 per ADS. Net proceeds were approximately $132.8 million, after deducting underwriting discounts and commissions and other offering expenses. COMPASS Pathways plc is a continuation of COMPASS Pathfinder Holdings Limited and its subsidiaries, and the corporate reorganization has been accounted for as a combination of entities under common control. The corporate reorganization associated with the IPO has been given retrospective effect in these historical unaudited condensed consolidated financial statements and such financial statements represent the financial statements of COMPASS Pathways plc. In connection with the corporate reorganization, outstanding restricted share awards and option grants of COMPASS Pathfinder Holdings Limited were exchanged for share awards and option grants of COMPASS Pathways plc with identical restrictions. The Company is subject to risks and uncertainties common to early-stage companies in the biotechnology industry, including, but not limited to, development by competitors of new technological innovations, dependence on key personnel, protection of proprietary technology, compliance with government regulations and the ability to secure additional capital to fund operations. Therapeutic candidates currently under development will require significant additional research and development efforts, including preclinical and clinical testing and regulatory approval, prior to commercialization. These efforts require significant amounts of capital, adequate personnel and infrastructure and extensive compliance-reporting capabilities. Even if the Company’s therapeutic development efforts are successful, it is uncertain when, if ever, the Company will realize revenue from sales. The Company has funded its operations primarily with proceeds from the sale of its convertible preferred shares, the issuance of convertible notes, and more recently through the sale of American Depository Shares in connection with the September 2020 IPO and its $154.8 million May 2021 follow-on offering, including the underwriters’ exercise of their over-allotment option. On October 8, 2021, the Company entered into a Sales Agreement with Cowen and Company, LLC (“Cowen”), under which the Company may issue and sell from time to time up to $150,000,000 of its ADSs, each representing one ordinary share, through Cowen as the sales agent. Sales of our ADSs, if any, will be made at market prices. The Company has incurred recurring losses since its inception, including net losses of $46.1million and $41.5 million for the nine months ended September 30, 2021 and 2020, respectively. In addition, as of September 30, 2021, the Company had an accumulated deficit of $144.0 million. The Company expects to continue to generate operating losses for the foreseeable future. The future viability of the Company is dependent on its ability to raise additional capital to finance its operations. The Company’s inability to raise capital as and when needed could have a negative impact on its financial condition and ability to pursue its business strategies. There can be no assurance that the current operating plan will be achieved or that additional funding will be available on terms acceptable to the Company, or at all. The Company believes the cash and cash equivalents on hand as of September 30, 2021 of $294.0 million will be sufficient to fund its operating expenses and capital expenditure requirements through to 2024. The Company continues to assess its business plans and the impact which the ongoing COVID-19 pandemic may have on its ability to advance the development and manufacturing of COMP360 as a result of adverse impacts on the research sites, service providers, vendors, or suppliers on whom it relies, or to raise further financing to support the development of its investigational COMP360 psilocybin therapy. No assurances can be given that this analysis will enable the Company to avoid any future impact from the ongoing COVID-19 pandemic or the emergency of new variants, including downturns in business sentiment generally or in its sector in particular. The Company cannot currently predict the scope and severity of any future potential business shutdowns or disruptions, but if the Company or any of the third parties on whom it relies or with whom the Company conducts business were to experience additional

Summary of Significant Accounti

Summary of Significant Accounting Policies	9 Months Ended
	Sep. 30, 2021
Accounting Policies [Abstract]
Summary of Significant Accounting Policies	Summary of Significant Accounting Policies Basis of Presentation The accompanying unaudited condensed consolidated financial statements have been prepared in conformity with accounting principles generally accepted in the United States of America, or U.S. GAAP. The unaudited condensed consolidated interim financial statements have been prepared on the same basis as the audited annual consolidated financial statements as of and for the year ended December 31, 2020, and, in the opinion of management, reflect all adjustments, consisting of normal recurring adjustments, necessary for the fair statement of the Company’s financial position as of September 30, 2021, and the results of its operations and comprehensive loss for the three months and nine months ended September 30, 2021 and 2020, and its cash flows for the nine months ended September 30, 2021 and 2020. The results for the three months and nine months ended September 30, 2021 are not necessarily indicative of the results to be expected for the year ending December 31, 2021, any other interim periods, or any future year or period. These interim financial statements should be read in conjunction with the audited financial statements as of and for the year ended December 31, 2020, and the notes thereto, which are included elsewhere in the Company’s 20-F filed with the U.S. Securities and Exchange Commission, or SEC, on March 9, 2021. Principles of Consolidation The accompanying condensed consolidated financial statements include the accounts of the Company and its wholly-owned subsidiaries. All intercompany balances and transactions have been eliminated in consolidation. Use of Estimates The preparation of the condensed consolidated financial statements in conformity with U.S. GAAP requires management to make estimates and assumptions that affect the reported amounts of assets and liabilities, the disclosure of contingent assets and liabilities at the date of the condensed consolidated financial statements and the reported amounts of income and expenses during the reporting periods. Significant estimates and assumptions reflected in these condensed consolidated financial statements include, but are not limited to, the accrual for research and development expenses, the fair value of ordinary shares prior to the Company’s IPO, share-based compensation, measurement of the fair value of the Company’s convertible notes and the research and development tax credit. Estimates are periodically reviewed in light of changes in circumstances, facts and experience. Changes in estimates are recorded in the period in which they become known. Actual results could differ materially from those estimates. Cash and Cash Equivalents The Company considers all highly liquid investments that have maturities of three months or less when acquired to be cash equivalents. The Company does not currently have any cash equivalents. Restricted Cash Restricted cash as of September 30, 2021 and December 31, 2020 represents a collateral deposit for employee credit cards. Investment The investment does not have readily determinable fair value and it is carried at cost, less impairment, adjusted for subsequent changes to estimated fair value up to the original cost, in circumstances where the Company does not have the ability to exercise significant influence or control over the operating and financial policies of the investee. Fair Value of Financial Instruments Certain liabilities of the Company were carried at fair value under U.S. GAAP. Fair value is defined as the exchange price that would be received for an asset or paid to transfer a liability (an exit price) in the principal or most advantageous market for the asset or liability in an orderly transaction between market participants on the measurement date. Valuation techniques used to measure fair value must maximize the use of observable inputs and minimize the use of unobservable inputs. Financial assets and liabilities carried at fair value are to be classified and disclosed in one of the following three levels of the fair value hierarchy, of which the first two are considered observable and the last is considered unobservable: • Level 1—Quoted prices in active markets for identical assets or liabilities. • Level 2—Observable inputs (other than Level 1 quoted prices), such as quoted prices in active markets for similar assets or liabilities, quoted prices in markets that are not active for identical or similar assets or liabilities, or other inputs that are observable or can be corroborated by observable market data. • Level 3—Unobservable inputs that are supported by little or no market activity that are significant to determining the fair value of the assets or liabilities, including pricing models, discounted cash flow methodologies and similar techniques. The Company's convertible notes issued prior to IPO were classified within Level 3 of the fair value hierarchy because their fair values were estimated by utilizing valuation models and significant unobservable inputs. The convertible notes were valued using a scenario-based discounted cash flow analysis. Two primary scenarios were considered and probability weighted to arrive at the valuation conclusion for each convertible note. The first scenario considered the value impact of conversion at the stated discount to the issue price if the Company raised over £25.0 million in an equity financing before the first anniversary of the issuance date, the Qualified Financing, or otherwise converted in a Non-Qualified Financing, while the second scenario assumed the convertible notes were held to maturity. As of the issuance date of the convertible notes, an implied yield was calculated such that the probability weighted value of the convertible note was equal to the principal investment amount. The implied yield of previously issued convertible notes was carried forward and used as the primary discount rate for subsequent valuation dates. The Company estimated the fair value of the convertible notes based on a future value on projected conversion dates which have been i) discounted back to the valuation date at an appropriate discount rate and ii) probability weighted to arrive at an indication of value for the convertible notes. On April 17, 2020, the Company closed a Series B funding round to secure an additional $80.0 million of funding, including the conversion of the $18.4 million (£15.0 million) convertible loan notes issued in 2019 through the issuance of new B convertible preference shares (See Note 8). At September 30, 2021, the Company did not hold any convertible notes. Fair Value Option As permitted under Accounting Standards Codification, or ASC, 825, Financial Instruments, or ASC 825, the Company elected the fair value option to account for its convertible notes. In accordance with ASC 825, the Company recorded these convertible notes at fair value with changes in fair value recorded as a component of other income (expense), net in the condensed consolidated statements of operations and comprehensive loss. As a result of applying the fair value option, direct costs and fees related to the convertible notes were expensed as incurred and were not deferred. The Company concluded that it was appropriate to apply the fair value option to the convertible notes because there were no non-contingent beneficial conversion options related to the convertible notes. Concentration of Credit Risk Financial instruments that subject the Company to credit risk consist primarily of cash and cash equivalents. The Company places cash and cash equivalents in established financial institutions. The Company has no significant off-balance-sheet risk or concentration of credit risk, such as foreign exchange contracts, options contracts, or other foreign hedging arrangements. Property and Equipment Property and equipment are recorded at cost and depreciated using the straight-line method over the estimated useful lives of the respective assets, which are as follows: Estimated Useful Life Lab equipment 5 years Office equipment 3-5 years Furniture and fixtures 3 years Leasehold improvements Shorter of useful life or remaining lease term Upon retirement or sale, the cost of assets disposed of and the related accumulated depreciation are removed from the accounts and any resulting gain or loss is included in the condensed consolidated statements of operations and comprehensive loss. Expenditures for repairs and maintenance are charged to expense as incurred. Impairment of Long-Lived Assets The Company evaluates assets for potential impairment when events or changes in circumstances indicate the carrying value of the assets may not be recoverable. Recoverability is measured by comparing the book values of the assets to the expected future net undiscounted cash flows that the assets are expected to generate. If such assets are considered to be impaired, the impairment to be recognized is measured by the amount by which the book values of the assets exceed their fair value. The Company has not recognized any impairment losses or had triggering events related to its underlying assets for the three months and nine months ended September 30, 2021 and 2020. Segment Information Operating segments are defined as components of an enterprise about which separate discrete information is available for evaluation by the chief operating decision maker in deciding how to allocate resources and assess performance. The Company and the Company’s chief operating decision maker, the Company’s Chief Executive Officer, view the Company’s operations and manages its business as a single operating segment; however, the Company operates in two geographic regions: the UK and the United States. The Company’s fixed assets are primarily located in the UK. The Company’s singular concentration is focused on accelerating patient access to evidence-based innovation in mental health. Research and Development Costs Research and development costs are expensed as incurred. Research and development expenses consist of costs incurred in performing research and development activities, including salaries, share-based compensation and benefits, travel, and external costs of outside vendors engaged to conduct clinical development activities, clinical trials and the cost to manufacture clinical trial materials. Research Contract Costs, Accruals and Prepayments The Company has entered into various research and development-related contracts with research institutions and other companies. These agreements are generally cancelable, and related payments are recorded as research and development expenses as incurred. The Company records accruals and prepayments for estimated ongoing research costs and receives updated estimates of costs and amounts owed on a monthly basis from its third-party service providers. When evaluating the adequacy of the accrued liabilities and prepaid assets, the Company analyzes progress of the studies or clinical trials, including the phase or completion of events, invoices received and contracted cost estimates from third-party service providers. Estimates are made in determining the accrued and prepaid balances at the end of any reporting period. Actual results could differ from the Company’s estimates. The Company’s historical accrual and prepayment estimates have not been materially different from the actual costs. Share-Based Compensation The Company accounts for all share-based payment awards granted to employees and non-employees as share-based compensation expense at fair value. The Company grants equity awards under its share-based compensation programs, which may include share options and restricted ordinary shares. The measurement date for employee and non-employee awards is the date of grant, and share-based compensation costs are recognized as expense over the requisite service period, which is the vesting period, on a straight-line basis. Share-based compensation expense is classified in the accompanying condensed consolidated statements of operations and comprehensive loss based on the function to which the related services are provided. The Company recognizes share-based compensation expense for the portion of awards that have vested. Forfeitures are recorded as they occur. There have been no performance conditions attached to the share options granted by the Company to date. The fair value of each share option grant is estimated on the date of grant using the Black-Scholes option pricing model. See Note 11 for the Company’s assumptions used in connection with option grants made during the periods covered by these condensed consolidated financial statements. Assumptions used in the option pricing model include the following: Expected volatility. The Company lacks company-specific historical and implied volatility information for its ordinary shares. Therefore, it estimates its expected share volatility based on the historical volatility of publicly traded peer companies and expects to continue to do so until such time as it has adequate historical data regarding the volatility of its own traded share price. Expected term. The expected term of the Company’s share options has been determined utilizing the “simplified” method for awards that qualify as “plain-vanilla” options. Risk-free interest rate. The risk-free interest rate is determined by reference to the U.S. Treasury yield curve in effect at the time of grant of the award for time periods that are approximately equal to the expected term of the award. Expected dividend. The expected dividend yield of zero is based on the fact that the Company has never paid cash dividends on ordinary shares and does not expect to pay any cash dividends in the foreseeable future. Fair value of ordinary shares. Given the absence of an active market for the Company’s ordinary shares prior to the IPO, the Company and its board of directors, the members of which the Company believes have extensive business, finance, and venture capital experience, were required to estimate the fair value of the Company’s ordinary shares at the time of each grant of a stock-based award. The grant date fair values of restricted ordinary shares and share options were calculated based on the grant date fair value of the underlying ordinary shares. The Company calculated the fair value of the ordinary shares in accordance with the guidelines in the American Institute of Certified Public Accountants’ Accounting and Valuation Guide, Valuation of Privately-Held-Company Equity Securities Issued as Compensation, or the “Practice Aid”. The Company’s valuations of ordinary shares were prepared using a market approach, based on precedent transactions in the shares, to estimate the Company’s total equity value using an option-pricing method, or OPM. After the IPO, the fair value of ordinary shares is determined by reference to the closing price of ADSs on the Nasdaq Global Select Market on the date prior to the grant date. The OPM derives an equity value such that the value indicated for ordinary shares is consistent with the investment price, and it provides an allocation of this equity value to each of the Company’s securities. The OPM treats the various classes of ordinary shares as call options on the total equity value of a company, with exercise prices based on the value thresholds at which the allocation among the various holders of a company’s securities changes. Under this method, the ordinary shares have value only if the funds available for distribution to shareholders exceeded the value of the share liquidation preferences of ordinary shares with senior preferences at the time of the liquidity event. Key inputs into the OPM calculation included the risk-free rate, expected time to liquidity and volatility. A reasonable discount for lack of marketability was applied to the total equity value to arrive at an estimate of the total fair value of equity on a non-marketable basis. Foreign Currency Translation The Company maintains its condensed consolidated financial statements in its functional currency, which is Pound Sterling. Monetary assets and liabilities denominated in currencies other than the functional currency are translated into the functional currency at rates of exchange prevailing at the balance sheet dates. Non-monetary assets and liabilities denominated in foreign currencies are translated into the functional currency at the exchange rates prevailing at the date of the transaction. Exchange gains or losses arising from foreign currency transactions are included in other income (expense), net in the condensed consolidated statements of operations and comprehensive loss. For financial reporting purposes, the condensed consolidated financial statements of the Company have been presented in U.S. dollars, the reporting currency. The financial statements of entities are translated from their functional currency into the reporting currency as follows: assets and liabilities are translated at the exchange rates at the balance sheet dates, expenses and other income (expense), net are translated at the average exchange rates for the relevant period and shareholders’ deficit is translated based on historical exchange rates. Translation adjustments are not included in determining net loss but are included as a foreign exchange adjustment to other comprehensive income (loss), a component of shareholders’ equity. Income Taxes The Company accounts for income taxes using the asset and liability method, which requires the recognition of deferred tax assets and liabilities for the expected future tax consequences of events that have been recognized in the condensed consolidated financial statements or in its tax returns. Deferred tax assets and liabilities are determined on the basis of the differences between the condensed consolidated financial statements and tax basis of assets and liabilities using substantively enacted tax rates in effect for the year in which the differences are expected to reverse. Changes in deferred tax assets and liabilities are recorded in the provision for income taxes. The Company assesses the likelihood that deferred tax assets will be recovered in the future to the extent management believes, based upon the weight of available evidence, that it is more likely than not that all or a portion of the deferred tax assets will not be realized, a valuation allowance is established through a charge to income tax expense. Potential for recovery of deferred tax assets is evaluated by estimating the future taxable profits expected and considering prudent and feasible tax planning strategies. The Company accounts for uncertainty in income taxes in the condensed consolidated financial statements by applying a two-step process to determine the amount of tax benefit to be recognized. First, the tax position must be evaluated to determine the likelihood that it will be sustained upon external examination by the taxing authorities. If the tax position is deemed more-likely-than-not to be sustained, the tax position is then assessed as the amount of benefit to recognize in the condensed consolidated financial statements. The amount of benefits that may be used is the largest amount that has a greater than 50% likelihood of being realized upon ultimate settlement. The provision for income taxes includes the effects of any resulting tax reserves, or unrecognized tax benefits, that are considered appropriate, as well as the related net interest and penalties. As of September 30, 2021 and December 31, 2020, the Company has not identified any uncertain tax positions. The Company recognizes interest and penalties related to unrecognized tax benefits on the income tax expense line in the accompanying condensed consolidated statements of operations and comprehensive loss. As of September 30, 2021 and December 31, 2020 no accrued interest or penalties are included on the related tax liability line in the condensed consolidated balance sheets. Benefit from Research and Development Tax Credit As a company that carries out extensive research and development activities, the Company benefits from the UK research and development tax credit regime under the scheme for small or medium-sized enterprises, or SME. Under the SME regime, the Company is able to surrender some of its trading losses that arise from qualifying research and development activities for a cash rebate of up to 33.35% of such qualifying research and development expenditure. The Company meets the conditions of the SME regime. Qualifying expenditures largely comprise employment costs for research staff, consumables, outsourced contract research organization costs and utilities costs incurred as part of research projects. Certain subcontracted qualifying research and development expenditures are eligible for a cash rebate of up to 21.67%. A large portion of costs relating to research and development, clinical trials and manufacturing activities are eligible for inclusion within these tax credit cash rebate claims. The Company is subject to corporate taxation in the UK. Due to the nature of the business, the Company has generated losses since inception. The benefit from research and development, or R&D, tax credit is recognized in the condensed consolidated statements of operations and comprehensive loss as a component of other income (expense), net, and represents the sum of the research and development tax credit recoverable in the UK. The UK research and development tax credit is fully refundable to the Company and is not dependent on current or future taxable income. As a result, the Company has recorded the entire benefit from the UK research and development tax credit as a benefit which is included in net loss before income tax and accordingly, not reflected as part of the income tax provision. If, in the future, any UK research and development tax credits generated are needed to offset a corporate income tax liability in the UK, that portion would be recorded as a benefit within the income tax provision and any refundable portion not dependent on taxable income would continue to be recorded within other income (expense), net. The Company may not be able to continue to claim research and development tax credits under the SME regime in the future because it may no longer qualify as a small or medium-sized company. Further, changes to the EU State Aid cap to limit the total aid claimable in respect of a given project to €7.5 million may impact the Company's ability to claim R&D tax credits in future. Unsurrendered UK losses may be carried forward indefinitely to be offset against future taxable profits, subject to numerous utilization criteria and restrictions. The amount that can be offset each year is limited to £5.0 million plus an incremental 50% of UK taxable profits. Comprehensive Loss Comprehensive loss includes net loss as well as other changes in shareholders’ equity (deficit) that result from transactions and economic events other than those with shareholders. For the three months and nine months ended September 30, 2021 and 2020, the component of accumulated other comprehensive income is a foreign currency translation adjustment. Net Loss per Share The Company has reported losses since inception and has computed basic net loss per share attributable to ordinary shareholders by dividing net loss attributable to ordinary shareholders by the weighted-average number of ordinary shares outstanding for the period, without consideration for potentially dilutive securities. The Company computes diluted net loss per ordinary share after giving consideration to all potentially dilutive ordinary shares, including unvested ordinary shares, share options, convertible preferred shares, Series A convertible preferred shares and Series B convertible preferred shares outstanding during the period determined using the treasury-stock and if-converted methods, except where the effect of including such securities would be antidilutive. Because the Company has reported net losses since inception, these potential ordinary shares have been anti-dilutive and basic and diluted loss per share were the same for all periods presented. Recently Adopted Accounting Pronouncements In December 2019, the Financial Accounting Standard Board, or the FASB, issued Accounting Standard Update, or ASU, 2019-12, “Income Taxes - Simplifying the Accounting for Income Taxes (Topic 740),” or ASU 740, which simplifies the accounting for income taxes. The new guidance removes certain exceptions to the general principles in ASC 740 such as recognizing deferred taxes for equity investments, the incremental approach to performing intra-period tax allocation and calculating income taxes in interim periods. The standard also simplifies accounting for income taxes under U.S. GAAP by clarifying and amending existing guidance, including the recognition of deferred taxes for goodwill, the allocation of taxes to members of a consolidated group and requiring that an entity reflect the effect of enacted changes in tax laws or rates in the annual effective tax rate computation in the interim period that includes the enactment date. This guidance is effective for annual periods beginning after December 15, 2020, and interim periods thereafter; however, early adoption is permitted. The Company adopted this ASU as of January 1, 2021 and it has had no material impact on the condensed consolidated financial statements. Recently Issued Accounting Pronouncements Not Yet Adopted In February 2016, the Financial Accounting Standards Board, or the FASB, issued Accounting Standard Update, or ASU, No. 2016-02, (Topic 842) Leases, or ASU 2016-02. ASU 2016-02 requires an entity to recognize assets and liabilities arising from a lease for both financing and operating leases. The ASU will also require new qualitative and quantitative disclosures to help investors and other financial statement users better understand the amount, timing, and uncertainty of cash flows arising from leases. For public entities, ASU 2016-02 is effective for fiscal years beginning after December 15, 2018. As a result of the Company having elected the extended transition period for complying with new or revised accounting standards pursuant to Section 107(b) of the Jumpstart Our Business Startups Act of 2012, or the JOBS Act, ASU 2016-02 is effective for the Company for the year ended December 31, 2021, and all interim periods thereafter. Early adoption is permitted. In June 2020, the FASB issued 2020-05 which extended the adoption of ASU 2016-02 to the year ended December 31, 2022 and all interim periods thereafter. While early adoption is permitted, the Company intends to adopt for the year ended December 31, 2021, following the loss of Emerging Growth Company status effective January 01, 2022. In July 2018, the FASB issued ASU 2018-11 Leases – Targeted Improvements, or ASU 2018-11, intended to ease the implementation of the new lease standard for financial statement preparers by, among other things, allowing for an additional transition method. In lieu of presenting transition requirements to comparative periods, as previously required, an entity may now elect to show a cumulative effect adjustment on the date of adoption without the requirement to recast prior period financial statements or disclosures presented in accordance with ASU 2016-02. The Company is continuing to evaluate developments within the new lease guidance and is finalizing its evaluation of its existing population of contracts to ensure all contracts that meet the definition of a lease contract under the new standard are identified. The Company is currently evaluating the impact of adopting this guidance on the Company’s condensed consolidated financial statements and expects that its operating lease commitments will be subject to the new standard and recognized as right-of-use assets and operating lease liabilities upon adoption of this standard, which will increase the total assets and total liabilities that it reports relative to such amounts presented prior to adoption.

Fair Value Measurements

Fair Value Measurements	9 Months Ended
	Sep. 30, 2021
Fair Value Disclosures [Abstract]
Fair Value Measurements	Fair Value Measurements There are no financial instruments measured at fair value on a recurring basis as of September 30, 2021 and December 31, 2020. Management believes that the carrying amounts of the Company’s financial instruments, including cash and cash equivalents, accounts payable and accrued expenses approximate fair value due to the short-term nature of those instruments. The Company elected the fair value option to account for its convertible notes issued during 2019 (See Note 8). The fair value of the convertible notes was determined based on significant inputs not observable in the market, which represents a level 3 measurement within the fair value hierarchy. The Company recorded a loss of $1.8 million for changes in the fair value of the convertible notes in the condensed consolidated statements of operations and comprehensive loss for the nine months ended September 30, 2020. No change in fair value of convertible notes was recognized during the three months ended September 30, 2020. The following table provides a roll forward of the aggregate fair value of the Company’s convertible notes, for which fair value was determined using level 3 inputs (in thousands): Convertible notes Balance as of December 31, 2019 $ 21,089 Change in fair value 1,754 Settlement of convertible notes (21,614) Exchange difference (1,229) Balance as of September 30, 2020 $ —

Investment

Investment	9 Months Ended
	Sep. 30, 2021
Equity Method Investments and Joint Ventures [Abstract]
Investment	InvestmentOn March 6, 2020, the Company made a strategic investment of $0.5 million to acquire an 8% (on a fully diluted basis) shareholding in Delix Therapeutics, Inc., a drug discovery and development company researching novel small molecules for use in CNS indications. The Company’s investment in Delix Therapeutics, Inc. does not provide it with significant influence over the investee. The investment does not have a readily determinable fair value and therefore will be measured at cost minus impairment adjusted by observable price changes in orderly transactions for the identical or a similar investment of the same issuer. This investment will be measured at fair value on a nonrecurring basis when there are events or changes in circumstances that may have a significant adverse effect or require remeasurement. An impairment loss is recognized in the condensed consolidated statements of operations and comprehensive loss equal to the amount by which the carrying value exceeds the fair value of the investment. As of September 30, 2021, no impairment loss was recognized.

Prepaid Expenses and Other Curr

Prepaid Expenses and Other Current Assets	9 Months Ended
	Sep. 30, 2021
Deferred Costs, Capitalized, Prepaid, and Other Assets Disclosure [Abstract]
Prepaid Expenses and Other Current Assets	Prepaid Expenses and Other Current Assets Prepaid expenses and other current assets consisted of the following (in thousands) : September 30, December 31, 2021 2020 UK R&D tax credit $ 6,664 $ 4,610 Prepaid insurance premium 4,469 3,154 Prepaid research and development 4,920 2,317 VAT recoverable 1,394 1,171 Deferred offering costs 228 — Other current assets 1,058 796 $ 18,733 $ 12,048

Property and Equipment, Net

Property and Equipment, Net	9 Months Ended
	Sep. 30, 2021
Property, Plant and Equipment [Abstract]
Property and Equipment, Net	Property and Equipment, Net Property and equipment, net consisted of the following (in thousands): September 30, December 31, 2021 2020 Lab equipment $ 304 $ 130 Office equipment 313 260 Furniture and fixtures 37 37 Leasehold improvements 6 6 660 433 Less: accumulated depreciation (305) (188) $ 355 $ 245 Depreciation and amortization expense were less than $0.1 million and $0.1 million for the three months and nine months ended September 30, 2021, respectively. Depreciation and amortization expense were less than $0.1 million and $0.1 million for the three months and nine months ended September 30, 2020, respectively.

Accrued Expenses and Other Liab

Accrued Expenses and Other Liabilities	9 Months Ended
	Sep. 30, 2021
Other Liabilities Disclosure [Abstract]
Accrued Expenses and Other Liabilities	Accrued Expenses and Other Liabilities Accrued expenses and other liabilities consisted of the following (in thousands) : September 30, December 31, 2021 2020 Accrued research and development expense $ 2,233 $ 720 Accrued professional expenses 768 701 Accrued compensation and benefit costs 2,026 1,687 Payroll tax payable 530 384 Income taxes payable 581 243 Other liabilities 443 413 $ 6,581 $ 4,148

Convertible Notes

Convertible Notes	9 Months Ended
	Sep. 30, 2021
Debt Disclosure [Abstract]
Convertible Notes	Convertible NotesOn August 28, 2019, the Company entered into convertible note agreements for a total additional principal amount of $18.4 million (£15.0 million). The convertible notes issued in 2019 are collectively referred to as the “2019 Convertible Notes”. The 2019 Convertible Notes bore interest at 3% per annum and were payable concurrently with repayment of the principal amount. No repayment of principal or interest was due until maturity, which occurred 12 months after issuance of the 2019 Convertible Notes. Under the agreement, the 2019 Convertible Notes automatically convert (i) upon the completion of a Qualified Financing (as defined in the 2019 Convertible Notes); or (ii) if the noteholder majority approves a Non-Qualified Financing (as defined in the 2019 Convertible Notes) which constitutes a conversion event, which is triggered at a 15% discount of the per share price of the securities sold in either a Qualified Financing or Non-Qualified Financing (each as defined in the 2019 Convertible Notes). On April 17, 2020, upon the Series B convertible preferred share financing, which constituted a Qualified Financing under the terms of the 2019 Convertible Notes, the outstanding principal of the convertible notes of $18.4 million (£15.0 million) automatically converted into 1,723,263 Series B convertible preferred shares, and there was no outstanding balance of 2019 Convertible Notes as of September 30, 2021 and December 31, 2020. The Company elected the fair value option to account for the 2019 Convertible Notes. The Company recorded the 2019 Convertible Notes at fair value and subsequently remeasured them to fair value at each reporting date. Changes in fair value were recognized as a component of other income (expense), net in the condensed consolidated statements of operations and comprehensive loss. The Company recognized losses in the condensed consolidated statements of operations and comprehensive loss of $1.8 million as a change in fair value of the convertible notes during the nine months ended September 30, 2020. No change in fair value of convertible notes was recognized during the three months ended September 30, 2020 as no convertible notes were outstanding during the three months ended September 30, 2020.

Convertible Preferred Shares

Convertible Preferred Shares	9 Months Ended
	Sep. 30, 2021
Debt Disclosure [Abstract]
Convertible Preferred Shares	Convertible Preferred Shares Prior to the IPO, the Company had issued convertible preferred shares, Series A convertible preferred shares and Series B convertible preferred shares. In August 2017, the Company entered into a subscription and shareholders agreement, or the 2017 Agreements, pursuant to which the Company issued an aggregate of 2,650,980 convertible preferred shares for total proceeds of approximately $3.9 million and incurred issuance costs of $0.1 million, recorded as a reduction to convertible preferred shares. The 2017 Agreements were amended and restated in September 2018, as so amended, the Amended 2018 Agreements. Pursuant to the Amended 2018 Agreements, the Company issued 7,131,525 Series A convertible preferred shares for an aggregate purchase price of $35.4 million and incurred issuance costs of $0.3 million, recorded as a reduction to convertible preferred shares. On April 17, 2020, the Company closed a Series B funding round to secure an additional $80.0 million of funding, including the conversion of the 2019 Convertible Notes (see Note 8), through the issuance of Series B convertible preferred shares. The Company received $56.3 million in cash proceeds upon the issuance of 4,487,533 Series B convertible preferred shares in April 2020 and an additional $5.3 million upon the issuance of a further 425,871 Series B convertible preferred shares in August 2020 and incurred issuance costs of $0.3 million, recorded as a reduction to the convertible preferred shares during the nine months ended September 30, 2020. The 2019 Convertible Notes were converted into 1,723,263 Series B convertible preferred shares. The issuance price of the Series B convertible preferred shares was $1.42 per share. Convertible preferred shares and Series A convertible preferred shares consisted of the following as of December 31, 2019 (in thousands, except for share amounts): Shares Liquidation Preference Carrying Value Authorized Outstanding Convertible preferred shares 2,650,980 2,650,980 $ 3,865 $ 3,761 Series A convertible preferred shares 7,131,525 7,131,525 35,414 35,147 9,782,505 9,782,505 $ 39,279 $ 38,908 Upon closing of the IPO, the convertible preferred shares and Series A convertible preferred shares as of December 31, 2019, together with the Series B convertible preferred shares issued during the nine months ended September 30, 2020, were converted to 16,419,172 ordinary shares. The holders of the Company’s convertible preferred shares, Series A and Series B convertible preferred shares had certain voting, dividend, and redemption rights, as well as liquidation preferences and conversion privileges. All rights, preferences, and privileges associated with the convertible preferred shares, Series A convertible preferred shares and Series B convertible preferred shares were terminated at the time of the Company’s IPO in conjunction with the conversion of all outstanding shares of convertible preferred shares, Series A convertible preferred shares and Series B convertible preferred shares into ordinary shares.

Ordinary Shares

Ordinary Shares	9 Months Ended
	Sep. 30, 2021
Equity [Abstract]
Ordinary Shares	Ordinary Shares In August 2017, the Company issued 10,551,166 ordinary shares for services rendered to the Company at a nominal value of £0.008 per share. In connection with the issuance of convertible preferred shares in August 2017, vesting conditions were placed on the 10,551,166 shares. These shares vested as follows: 25% of the shares held by certain of the founders vested on August 17, 2017; 25% of the shares vested on August 17, 2018; and 50% of shares vested in twenty-four equal monthly installments from August 17, 2018 through August 17, 2020. The fair value of the ordinary shares issued to certain of the founders in excess of the consideration initially paid was recognized as share-based compensation over the vesting period. In October 2019, the Company issued 102,214 and 99,049 ordinary shares to a non-employee and an employee, with the vesting period of three On September 22, 2020, the Company closed its IPO of ADSs representing its ordinary shares and issued and sold 8,625,000 ADSs at a public offering price of $17.00 per ADS, resulting in net proceeds of approximately $132.8 million after deducting underwriting fees and offering costs. Upon the closing of the IPO, the convertible preferred shares and Series A convertible preferred shares and Series B convertible preferred shares were converted to 16,419,172 ordinary shares. On May 4, 2021, the Company sold 4,000,000 ordinary shares in connection with its follow-on offering. On May 19, 2021, the underwriters exercised their option to purchase an additional 600,000 ordinary shares. This capital raise resulted in net proceeds of approximately $154.8 million after deducting underwriting fees and offering costs. In the nine months ended September 30, 2021, the Company issued in total 1,188,242 ordinary shares to settle share options exercised by employees and non-employees, of which 232,227 ordinary shares related to options exercised in 2020, with subsequent share issuances in 2021. 59,900 options were exercised at nominal value on September 30, 2021 with the associated ordinary shares subsequently issued on October 1, 2021, hence, they are not included in the total of 1,188,242 ordinary shares above. In the nine months ended September 30, 2021, 56,887 restricted share units vested,of which, 12,607 ordinary shares were issued in settlement of the vested restricted shares units on August 13, 2021. No ordinary shares were issued for the vested restricted share units of 44,280 in May and August 2021.

Share-Based Compensation

Share-Based Compensation	9 Months Ended
	Sep. 30, 2021
Share-based Payment Arrangement [Abstract]
Share-Based Compensation	Share-Based Compensation 2017 Equity Incentive Plan Under the Company’s prior shareholder and subscription agreements, the Company was authorized to issue restricted shares, restricted share units, as well as options, as incentives to its employees, non-employees and members of its board of directors. To the extent such incentives are in the form of share options, the options are granted pursuant to the terms of the 2017 Equity Incentive Plan, or the 2017 Plan. In July 2019, the Company’s board of directors adopted the 2017 Plan. The 2017 Plan provides for the grant of Enterprise Management Incentive, or EMI, options, to its UK employees, for the grant of options to its U.S. employees and non-employees of the Company. The 2017 Plan is administered by the board of directors. As of September 30, 2021 , the Company was authorized under the shareholder agreements to issue a total of 13,601,246 ordinary shares, including shares underlying options granted pursuant to the 2017 Plan. Forfeitures are accounted for as they occur. As of September 30, 2021, there were 445,943 shares available for issuance as incentives to the Company’s employees and directors, which includes shares underlying options that may be granted from time to time subsequent to September 30, 2021 under the terms of the 2017 Plan. 12,607 ordinary shares were issued for 56,887 restricted share units that vested during the nine months ended September 30, 2021. Options granted under the 2017 Plan typically vest over a three The options granted on June 30, 2020 are subject to 25% vesting upon the earlier occurrence of (i) the one year anniversary of the date of grant, or (ii) the date of the listing of the Company's ordinary shares on any stock exchange, followed by straight line vesting for three years for the remaining 75% of the allocation until vested in full. The restricted share units granted on June 30, 2020 are subject to 25% vesting upon the earlier of (i) the one year anniversary of the date of grant, or (ii) the first day following the six-month anniversary of the listing of the Company's ordinary shares on any stock exchange on which the closing price of the shares is 20% higher than the listing price for at least five consecutive trading days, provided the Company is in a trading window permitted by the Company’s Dealing Code. The remainder vests at 6.25% on the first day of the month that is three months following that in which the initial vesting date occurs, and on the expiry of each subsequent three-month period thereafter for 11 such periods. Options granted under the 2017 Plan generally expire 10 years from the date of grant. 2020 Share Option Plan In September 2020, the Company’s board of directors adopted, and the Company’s shareholders approved, the 2020 Share Option Plan, or (the “2020 Plan”), which became effective upon the effectiveness of the Company’s Registration Statement on Form F-1 in connection with the IPO. The 2020 Plan allows the compensation and leadership development committee to make equity-based and cash-based incentive awards to the Company’s officers, employees, directors and other key persons (including consultants). As of September 30, 2021, the Company has not granted any cash-based incentive awards. The Company initially reserved 2,074,325 of its ordinary shares for the issuance of awards under the 2020 Plan. The 2020 Plan provides that the number of shares reserved and available for issuance under the plan will automatically increase each January 1, beginning on January 1, 2022, by up to 4% of the outstanding number of ordinary shares on the immediately preceding December 31, or such lesser number of shares as determined by our compensation and leadership development committee. This number is subject to adjustment in the event of a sub-division, consolidation, share dividend or other change in our capitalization. The total number of ordinary shares that may be issued under the 2020 Plan was 2,074,325 shares as of September 30, 2021, of which 494,809 shares remained available for future grants. During the nine months ended September 30, 2021 and 2020, the Company granted options to purchase 752,702 and 3,150,360 ordinary shares to employees and non-employees, respectively. Ordinary Shares A summary of the changes in the Company’s unvested ordinary shares during the nine months ended September 30, 2021 are as follows: Number of Shares Weighted Average Grant Date Fair Value Unvested and Outstanding as of December 31, 2020 13,757 $ 2.36 Granted — — Vested (13,757) 2.36 Forfeited — — Unvested and Outstanding as of September 30, 2021 — $ — The total fair value of vested shares was less than $0.1 million and $1.2 million for the nine months ended September 30, 2021 and 2020, respectively. Restricted Share Units A summary of the changes in the Company’s unvested restricted share units during the nine months ended September 30, 2021 are as follows: Number of Shares Weighted Average Grant Date Fair Value Unvested and Outstanding as of December 31, 2020 217,482 $ 10.19 Granted — — Vested (56,887) 10.19 Forfeited — — Unvested and Outstanding as of September 30, 2021 160,595 $ 10.19 As of September 30, 2021 , there was $1.6 million of unrecognized compensation cost related to unvested restricted share units, which is expected to be recognized over a weighted-average period of 2.8 years. The exercise price of restricted share units is at a nominal value less than £0.01 per share. 12,607 ordinary shares were issued for 56,887 restricted share units that vested during the nine months ended September 30, 2021. Share Options The following table summarizes the Company’s share options activity for the nine months ended September 30, 2021 : Number of Shares Weighted Average Exercise Price Weighted Average Remaining Contractual Term (Years) Aggregate Intrinsic Value (in thousands) Outstanding as of December 31, 2020 4,430,340 $ 5.61 9.22 $ 186,426 Granted 752,702 $ 37.20 Exercised (1,015,915) $ 1.07 Forfeited (74,631) $ 9.11 Outstanding as of September 30, 2021 4,092,496 $ 12.18 8.79 $ 81,351 Exercisable as of September 30, 2021 2,294,380 $ 1.92 8.45 $ 64,148 Unvested as of September 30, 2021 1,798,116 $ 24.47 9.23 $ 17,203 The weighted average exercise price of options granted to UK employees during the nine months ended September 30, 2020 was $4.00 per share. The weighted average exercise price of options granted to United States employees during the nine months ended September 30, 2020 was $4.72 per share. The aggregate intrinsic value of share options is calculated as the difference between the exercise price of the share options and the fair value of the Company’s ordinary shares for those share options that had exercise prices lower than the fair value of the Company’s ordinary shares. The weighted average grant-date fair value of share options granted was $22.71 and $8.25 per share during the nine months ended September 30, 2021 and 2020, respectively. As of September 30, 2021, there was $27.6 million of unrecognized compensation cost related to unvested share options, which is expected to be recognized over a weighted-average period of 3.2 years. Share Option Valuation The weighted-average assumptions used in the Black-Scholes option pricing model to determine the fair value of the share options granted to employees and directors during the three months and nine months ended September 30, 2021 and 2020 were as follows: Three Months Ended September 30, Nine Months Ended September 30, 2021 2020 2021 2020 Expected term (in years) 6.07 Years 6.08 Years 6.07 Years 5.93 Years Expected volatility 66.90 % 66.90 % 67.20 % 66.00 % Risk-free interest rate 0.96 % 0.39 % 0.91 % 0.43 % Expected dividend yield — % — % — % — % Fair value of underlying ordinary shares $ 34.83 $ 17.00 $ 37.65 $ 10.30 Share-based Compensation Expense Share-based compensation expense recorded as research and development and general and administrative expenses is as follows (in thousands): Three Months Ended September 30, Nine Months Ended September 30, 2021 2020 2021 2020 Research and development $ 1,288 $ 2,231 $ 3,023 $ 5,748 General and administrative 999 2,984 2,834 10,869 Total share-based compensation expense $ 2,287 $ 5,215 $ 5,857 $ 16,617

Net Loss Per Share

Net Loss Per Share	9 Months Ended
	Sep. 30, 2021
Earnings Per Share [Abstract]
Net Loss Per Share	Net Loss Per Share Basic and diluted net loss per share attributable to ordinary shareholders was calculated as follows (in thousands, except share and per share amounts): Three Months Ended September 30, Nine Months Ended September 30, 2021 2020 2021 2020 Numerator Net loss $ (15,849) $ (16,694) $ (46,092) $ (41,528) Net loss attributable to ordinary shareholders - basic and diluted $ (15,849) $ (16,694) $ (46,092) $ (41,528) Denominator Weighted-average number of ordinary shares used in net loss per share - basic and diluted 41,708,220 12,834,889 39,378,824 10,638,738 Net loss per share - basic and diluted $ (0.38) $ (1.30) $ (1.17) $ (3.90) The Company’s potentially dilutive securities, which include unvested ordinary shares, unvested restricted share units, convertible preferred shares, Series A convertible preferred shares, Series B convertible preferred shares and options granted, have been excluded from the computation of diluted net loss per share as the effect would be to reduce the net loss per share. Therefore, the weighted-average number of ordinary shares outstanding used to calculate both basic and diluted net loss per share attributable to ordinary shareholders is the same. The Company excluded the following potential ordinary shares, presented based on amounts outstanding at each period end, from the computation of diluted net loss per share attributable to ordinary shareholders for the three months and nine months ended September 30, 2021 and 2020 because including them would have had an anti-dilutive effect: Three Months Ended September 30, Nine Months Ended September 30, 2021 2020 2021 2020 Unvested restricted shares — 22,011 — 22,011 Unvested restricted share units 160,595 257,708 160,595 257,708 Vested restricted share units, for which shares are not in issue 44,280 — 44,280 — Share options 4,092,496 4,482,507 4,092,496 4,482,507 4,297,371 4,762,226 4,297,371 4,762,226

Commitments and Contingencies

Commitments and Contingencies	9 Months Ended
	Sep. 30, 2021
Commitments and Contingencies Disclosure [Abstract]
Commitments and Contingencies	Commitments and Contingencies Legal Proceedings From time to time, the Company may be a party to litigation or subject to claims incident to the ordinary course of business. The Company was not a party to any material litigation and did not have material contingency reserves established for any liabilities as of September 30, 2021 and December 31, 2020. Leases The Company’s corporate headquarters is located in London, United Kingdom, for which, as of September 30, 2021 and 2020, the Company leases a series of office space at 19 Eastbourne Terrace, London, United Kingdom from The Office Group under a non-cancelable lease. The lease related to this facility is classified as an operating lease over a two year term. The Company recognizes rent expense on a straight-line basis over the respective lease period. On July 9, 2021, the Company entered into a two year non-cancellable lease beginning September 1, 2021 for office space at 33 Broadwick Street, London, United Kingdom which will become the Company’s new corporate headquarters. The Company leases office space at 180 Varick Street New York, USA from BioInnovations Labs, LLC under a cancelable lease that can be terminated by either party with one-month advanced notice. The lease related to this facility is classified as an operating lease. On August 3, 2021, the Company entered into a non-cancellable contract which expires in August 2022 to lease a series of office space at 164 Townsend Street, Suite 3, San Francisco, California, USA from Movassate Family Trust. The lease related to this facility is classified as an operating lease. The following table summarizes the future minimum lease payments due under operating leases as of September 30, 2021 (in thousands): Year end December, 31 Amount 2021 $ 751 2022 1,913 2023 1,222 $ 3,886 The Company recorded rent expense totaling $1.1 million and $0.8 million for the nine months ended September 30, 2021 and 2020, respectively. Indemnification In the normal course of business, the Company enters into contracts and agreements that contain a variety of representations and warranties and provide for general indemnification. The Company’s exposure under these agreements is unknown because it involves claims that may be made against the Company in the future. To date, the Company has not paid any claims or been required to defend any action related to its indemnification obligations. However, the Company may record charges in the future as a result of these indemnification obligations. In accordance with its Articles of Association, the Company has indemnification obligations to its officers and directors for certain events or occurrences, subject to certain limits, while they are serving at the Company’s request in such capacity. There have been no claims to date, and the Company has director and officer insurance that may enable it to recover a portion of any amounts paid for future potential claims.

Related Party Transactions

Related Party Transactions	9 Months Ended
	Sep. 30, 2021
Related Party Transactions [Abstract]
Related Party Transactions	Related Party TransactionsThe Company receives accounting and professional services from Tapestry Networks, Inc., or Tapestry, a company affiliated with the Company’s Chief Executive Officer and a director from time to time as needed. The Company recorded accounting and professional fees totaling less than $0.1 million for the nine months ended September 30, 2021 and $0.1 million for the nine months ended September 30, 2020. The Company recorded accounting and professional fees totaling less than $0.1 million for the three months ended September 30, 2021 and 2020. As of September 30, 2021 and 2020, the Company had less than $0.1 million outstanding to Tapestry.

Employee Benefit Plans

Employee Benefit Plans	9 Months Ended
	Sep. 30, 2021
Retirement Benefits [Abstract]
Employee Benefit Plans	Employee Benefit PlansIn the UK, the Company makes contributions to private defined contribution pension schemes on behalf of its employees. The Company paid $0.2 million and less than $0.1 million in contributions for the nine months ended September 30, 2021 and 2020, respectively.

Subsequent Events

Subsequent Events	9 Months Ended
	Sep. 30, 2021
Subsequent Events [Abstract]
Subsequent Events	Subsequent Events On October 1, 2021, the Company launched the Share Incentive Plan (SIP) and Employee Share Purchase Plan (ESPP), through which employees can purchase shares at a discounted price. 340,053 ordinary shares are currently available for future issuance under our Employee Stock Purchase Plan, or ESPP. On November 3, 2021, we announced that we will be conducting a phase II clinical trial to assess the safety and tolerability of COMP360 psilocybin therapy in post-traumatic stress disorder (PTSD). The study expands COMPASS’s research pipeline in COMP360 psilocybin therapy. It is a multicenter, fixed-dose open label study and will enroll 20 participants; it will begin at The Institute of Psychiatry, Psychology & Neuroscience (IoPPN) at King’s College London. On November 9, 2021, we announced positive topline results from our Phase IIb clinical trial evaluating COMP360 in conjunction with psychological support for the treatment of treatment-resistant depression. This is the largest, randomised, controlled, double-blind psilocybin therapy clinical trial ever completed. The topline results from the 233-participant trial showed a rapid and sustained response for patients receiving a single dose of COMP360 psilocybin with psychological support. The trial achieved its primary endpoint for the highest dose, with a 25mg dose of COMP360 demonstrating a statistically significant (p<0.001) and clinically relevant reduction in depressive symptom severity after three weeks.

Summary of Significant Accoun_2

Summary of Significant Accounting Policies (Policies)	9 Months Ended
	Sep. 30, 2021
Accounting Policies [Abstract]
Basis of Presentation	Basis of Presentation The accompanying unaudited condensed consolidated financial statements have been prepared in conformity with accounting principles generally accepted in the United States of America, or U.S. GAAP. The unaudited condensed consolidated interim financial statements have been prepared on the same basis as the audited annual consolidated financial statements as of and for the year ended December 31, 2020, and, in the opinion of management, reflect all adjustments, consisting of normal recurring adjustments, necessary for the fair statement of the Company’s financial position as of September 30, 2021, and the results of its operations and comprehensive loss for the three months and nine months ended September 30, 2021 and 2020, and its cash flows for the nine months ended September 30, 2021 and 2020.
Principles of Consolidation	Principles of ConsolidationThe accompanying condensed consolidated financial statements include the accounts of the Company and its wholly-owned subsidiaries. All intercompany balances and transactions have been eliminated in consolidation.
Use of Estimates	Use of Estimates The preparation of the condensed consolidated financial statements in conformity with U.S. GAAP requires management to make estimates and assumptions that affect the reported amounts of assets and liabilities, the disclosure of contingent assets and liabilities at the date of the condensed consolidated financial statements and the reported amounts of income and expenses during the reporting periods. Significant estimates and assumptions reflected in these condensed consolidated financial statements include, but are not limited to, the accrual for research and development expenses, the fair value of ordinary shares prior to the Company’s IPO, share-based compensation, measurement of the fair value of the Company’s convertible notes and the research and development tax credit. Estimates are periodically reviewed in light of changes in circumstances, facts and experience. Changes in estimates are recorded in the period in which they become known. Actual results could differ materially from those estimates.
Cash and Cash Equivalents	Cash and Cash Equivalents The Company considers all highly liquid investments that have maturities of three months or less when acquired to be cash equivalents. The Company does not currently have any cash equivalents.
Restricted Cash	Restricted CashRestricted cash as of September 30, 2021 and December 31, 2020 represents a collateral deposit for employee credit cards.
Investment	Investment The investment does not have readily determinable fair value and it is carried at cost, less impairment, adjusted for subsequent changes to estimated fair value up to the original cost, in
Fair Value of Financial Instruments	Fair Value of Financial Instruments Certain liabilities of the Company were carried at fair value under U.S. GAAP. Fair value is defined as the exchange price that would be received for an asset or paid to transfer a liability (an exit price) in the principal or most advantageous market for the asset or liability in an orderly transaction between market participants on the measurement date. Valuation techniques used to measure fair value must maximize the use of observable inputs and minimize the use of unobservable inputs. Financial assets and liabilities carried at fair value are to be classified and disclosed in one of the following three levels of the fair value hierarchy, of which the first two are considered observable and the last is considered unobservable: • Level 1—Quoted prices in active markets for identical assets or liabilities. • Level 2—Observable inputs (other than Level 1 quoted prices), such as quoted prices in active markets for similar assets or liabilities, quoted prices in markets that are not active for identical or similar assets or liabilities, or other inputs that are observable or can be corroborated by observable market data. • Level 3—Unobservable inputs that are supported by little or no market activity that are significant to determining the fair value of the assets or liabilities, including pricing models, discounted cash flow methodologies and similar techniques. The Company's convertible notes issued prior to IPO were classified within Level 3 of the fair value hierarchy because their fair values were estimated by utilizing valuation models and significant unobservable inputs. The convertible notes were valued using a scenario-based discounted cash flow analysis. Two primary scenarios were considered and probability weighted to arrive at the valuation conclusion for each convertible note. The first scenario considered the value impact of conversion at the stated discount to the issue price if the Company raised over £25.0 million in an equity financing before the first anniversary of the issuance date, the Qualified Financing, or otherwise converted in a Non-Qualified Financing, while the second scenario assumed the convertible notes were held to maturity. As of the issuance date of the convertible notes, an implied yield was calculated such that the probability weighted value of the convertible note was equal to the principal investment amount. The implied yield of previously issued convertible notes was carried forward and used as the primary discount rate for subsequent valuation dates. The Company estimated the fair value of the convertible notes based on a future value on projected conversion dates which have been i) discounted back to the valuation date at an appropriate discount rate and ii) probability weighted to arrive at an indication of value for the convertible notes. On April 17, 2020, the Company closed a Series B funding round to secure an additional $80.0 million of funding, including the conversion of the $18.4 million (£15.0 million) convertible loan notes issued in 2019 through the issuance of new B convertible preference shares (See Note 8). At September 30, 2021, the Company did not hold any convertible notes.
Fair Value Option	Fair Value Option As permitted under Accounting Standards Codification, or ASC, 825, Financial Instruments, or ASC 825, the Company elected the fair value option to account for its convertible notes. In accordance with ASC 825, the Company recorded these convertible notes at fair value with changes in fair value recorded as a component of other income (expense), net in the condensed consolidated statements of operations and comprehensive loss. As a result of applying the fair value option, direct costs and fees related to the convertible notes were expensed as incurred and were not deferred. The Company concluded that it was appropriate to apply the fair value option to the convertible notes because there were no non-contingent beneficial conversion options related to the convertible notes.
Concentration of Credit Risk	Concentration of Credit Risk Financial instruments that subject the Company to credit risk consist primarily of cash and cash equivalents. The Company places cash and cash equivalents in established financial institutions. The Company has no significant off-balance-sheet risk or concentration of credit risk, such as foreign exchange contracts, options contracts, or other foreign hedging arrangements.
Property and Equipment	Property and Equipment Property and equipment are recorded at cost and depreciated using the straight-line method over the estimated useful lives of the respective assets, which are as follows: Estimated Useful Life Lab equipment 5 years Office equipment 3-5 years Furniture and fixtures 3 years Leasehold improvements Shorter of useful life or remaining lease term
Impairment of Long-Lived Assets	Impairment of Long-Lived Assets The Company evaluates assets for potential impairment when events or changes in circumstances indicate the carrying value of the assets may not be recoverable. Recoverability is measured by comparing the book values of the assets to the expected future net undiscounted cash flows that the assets are expected to generate. If such assets are considered to be impaired, the impairment to be recognized is measured by the amount by which the book values of the assets exceed their fair value. The Company has not recognized any impairment losses or had triggering events related to its underlying assets for the three months and nine months ended September 30, 2021 and 2020.
Segment Information	Segment Information Operating segments are defined as components of an enterprise about which separate discrete information is available for evaluation by the chief operating decision maker in deciding how to allocate resources and assess performance. The Company and the Company’s chief operating decision maker, the Company’s Chief Executive Officer, view the Company’s operations and manages its business as a single operating segment; however, the Company operates in two geographic regions: the UK and the United States. The Company’s fixed assets are primarily located in the UK. The Company’s singular concentration is focused on accelerating patient access to evidence-based innovation in mental health.
Research and Development Costs	Research and Development Costs Research and development costs are expensed as incurred. Research and development expenses consist of costs incurred in performing research and development activities, including salaries, share-based compensation and benefits, travel, and external costs of outside vendors engaged to conduct clinical development activities, clinical trials and the cost to manufacture clinical trial materials.
Research Contract Costs, Accruals and Prepayments	Research Contract Costs, Accruals and Prepayments The Company has entered into various research and development-related contracts with research institutions and other companies. These agreements are generally cancelable, and related payments are recorded as research and development expenses as incurred. The Company records accruals and prepayments for estimated ongoing research costs and receives updated estimates of costs and amounts owed on a monthly basis from its third-party service providers. When evaluating the adequacy of the
Share-Based Compensation	Share-Based Compensation The Company accounts for all share-based payment awards granted to employees and non-employees as share-based compensation expense at fair value. The Company grants equity awards under its share-based compensation programs, which may include share options and restricted ordinary shares. The measurement date for employee and non-employee awards is the date of grant, and share-based compensation costs are recognized as expense over the requisite service period, which is the vesting period, on a straight-line basis. Share-based compensation expense is classified in the accompanying condensed consolidated statements of operations and comprehensive loss based on the function to which the related services are provided. The Company recognizes share-based compensation expense for the portion of awards that have vested. Forfeitures are recorded as they occur. There have been no performance conditions attached to the share options granted by the Company to date. The fair value of each share option grant is estimated on the date of grant using the Black-Scholes option pricing model. See Note 11 for the Company’s assumptions used in connection with option grants made during the periods covered by these condensed consolidated financial statements. Assumptions used in the option pricing model include the following: Expected volatility. The Company lacks company-specific historical and implied volatility information for its ordinary shares. Therefore, it estimates its expected share volatility based on the historical volatility of publicly traded peer companies and expects to continue to do so until such time as it has adequate historical data regarding the volatility of its own traded share price. Expected term. The expected term of the Company’s share options has been determined utilizing the “simplified” method for awards that qualify as “plain-vanilla” options. Risk-free interest rate. The risk-free interest rate is determined by reference to the U.S. Treasury yield curve in effect at the time of grant of the award for time periods that are approximately equal to the expected term of the award. Expected dividend. The expected dividend yield of zero is based on the fact that the Company has never paid cash dividends on ordinary shares and does not expect to pay any cash dividends in the foreseeable future. Fair value of ordinary shares. Given the absence of an active market for the Company’s ordinary shares prior to the IPO, the Company and its board of directors, the members of which the Company believes have extensive business, finance, and venture capital experience, were required to estimate the fair value of the Company’s ordinary shares at the time of each grant of a stock-based award. The grant date fair values of restricted ordinary shares and share options were calculated based on the grant date fair value of the underlying ordinary shares. The Company calculated the fair value of the ordinary shares in accordance with the guidelines in the American Institute of Certified Public Accountants’ Accounting and Valuation Guide, Valuation of Privately-Held-Company Equity Securities Issued as Compensation, or the “Practice Aid”. The Company’s valuations of ordinary shares were prepared using a market approach, based on precedent transactions in the shares, to estimate the Company’s total equity value using an option-pricing method, or OPM. After the IPO, the fair value of ordinary shares is determined by reference to the closing price of ADSs on the Nasdaq Global Select Market on the date prior to the grant date. The OPM derives an equity value such that the value indicated for ordinary shares is consistent with the investment price, and it provides an allocation of this equity value to each of the Company’s
Foreign Currency Translation	Foreign Currency Translation The Company maintains its condensed consolidated financial statements in its functional currency, which is Pound Sterling. Monetary assets and liabilities denominated in currencies other than the functional currency are translated into the functional currency at rates of exchange prevailing at the balance sheet dates. Non-monetary assets and liabilities denominated in foreign currencies are translated into the functional currency at the exchange rates prevailing at the date of the transaction. Exchange gains or losses arising from foreign currency transactions are included in other income (expense), net in the condensed consolidated statements of operations and comprehensive loss. For financial reporting purposes, the condensed consolidated financial statements of the Company have been presented in U.S. dollars, the reporting currency. The financial statements of entities are translated from their functional currency into the reporting currency as follows: assets and liabilities are translated at the exchange rates at the balance sheet dates, expenses and other income (expense), net are translated at the average exchange rates for the relevant period and shareholders’ deficit is translated based on historical exchange rates. Translation adjustments are not included in determining net loss but are included as a foreign exchange adjustment to other comprehensive income (loss), a component of shareholders’ equity.
Income Taxes	Income Taxes The Company accounts for income taxes using the asset and liability method, which requires the recognition of deferred tax assets and liabilities for the expected future tax consequences of events that have been recognized in the condensed consolidated financial statements or in its tax returns. Deferred tax assets and liabilities are determined on the basis of the differences between the condensed consolidated financial statements and tax basis of assets and liabilities using substantively enacted tax rates in effect for the year in which the differences are expected to reverse. Changes in deferred tax assets and liabilities are recorded in the provision for income taxes. The Company assesses the likelihood that deferred tax assets will be recovered in the future to the extent management believes, based upon the weight of available evidence, that it is more likely than not that all or a portion of the deferred tax assets will not be realized, a valuation allowance is established through a charge to income tax expense. Potential for recovery of deferred tax assets is evaluated by estimating the future taxable profits expected and considering prudent and feasible tax planning strategies. The Company accounts for uncertainty in income taxes in the condensed consolidated financial statements by applying a two-step process to determine the amount of tax benefit to be recognized. First, the tax position must be evaluated to determine the likelihood that it will be sustained upon external examination by the taxing authorities. If the tax position is deemed more-likely-than-not to be sustained, the tax position is then assessed as the amount of benefit to recognize in the condensed consolidated financial statements. The amount of benefits that may be used is the largest amount that has a greater than 50% likelihood of being realized upon ultimate settlement. The provision for income taxes includes the effects of any resulting tax reserves, or unrecognized tax benefits, that are considered appropriate, as well as the related net interest and penalties. As of September 30, 2021 and December 31, 2020, the Company has not identified any uncertain tax positions.
Benefit from Research and Development Tax Credit	Benefit from Research and Development Tax Credit As a company that carries out extensive research and development activities, the Company benefits from the UK research and development tax credit regime under the scheme for small or medium-sized enterprises, or SME. Under the SME regime, the Company is able to surrender some of its trading losses that arise from qualifying research and development activities for a cash rebate of up to 33.35% of such qualifying research and development expenditure. The Company meets the conditions of the SME regime. Qualifying expenditures largely comprise employment costs for research staff, consumables, outsourced contract research organization costs and utilities costs incurred as part of research projects. Certain subcontracted qualifying research and development expenditures are eligible for a cash rebate of up to 21.67%. A large portion of costs relating to research and development, clinical trials and manufacturing activities are eligible for inclusion within these tax credit cash rebate claims. The Company is subject to corporate taxation in the UK. Due to the nature of the business, the Company has generated losses since inception. The benefit from research and development, or R&D, tax credit is recognized in the condensed consolidated statements of operations and comprehensive loss as a component of other income (expense), net, and represents the sum of the research and development tax credit recoverable in the UK. The UK research and development tax credit is fully refundable to the Company and is not dependent on current or future taxable income. As a result, the Company has recorded the entire benefit from the UK research and development tax credit as a benefit which is included in net loss before income tax and accordingly, not reflected as part of the income tax provision. If, in the future, any UK research and development tax credits generated are needed to offset a corporate income tax liability in the UK, that portion would be recorded as a benefit within the income tax provision and any refundable portion not dependent on taxable income would continue to be recorded within other income (expense), net. The Company may not be able to continue to claim research and development tax credits under the SME regime in the future because it may no longer qualify as a small or medium-sized company. Further, changes to the EU State Aid cap to limit the total aid claimable in respect of a given project to €7.5 million may impact the Company's ability to claim R&D tax credits in future. Unsurrendered UK losses may be carried forward indefinitely to be offset against future taxable profits, subject to numerous utilization criteria and restrictions. The amount that can be offset each year is limited to £5.0 million plus an incremental 50% of UK taxable profits.
Comprehensive Loss	Comprehensive Loss Comprehensive loss includes net loss as well as other changes in shareholders’ equity (deficit) that result from transactions and economic events other than those with shareholders. For the three months and nine months ended September 30, 2021 and 2020, the component of accumulated other comprehensive income is a foreign currency translation adjustment.
Net Loss per Share	Net Loss per Share The Company has reported losses since inception and has computed basic net loss per share attributable to ordinary shareholders by dividing net loss attributable to ordinary shareholders by the weighted-average number of ordinary shares outstanding for the period, without consideration for potentially dilutive securities. The Company computes diluted net loss per ordinary share after giving consideration to all potentially dilutive ordinary shares, including unvested ordinary shares, share options, convertible preferred shares, Series A convertible preferred shares and Series B convertible preferred
Recently Adopted and Recently Issued Accounting Pronouncements Not Yet Adopted	Recently Adopted Accounting Pronouncements In December 2019, the Financial Accounting Standard Board, or the FASB, issued Accounting Standard Update, or ASU, 2019-12, “Income Taxes - Simplifying the Accounting for Income Taxes (Topic 740),” or ASU 740, which simplifies the accounting for income taxes. The new guidance removes certain exceptions to the general principles in ASC 740 such as recognizing deferred taxes for equity investments, the incremental approach to performing intra-period tax allocation and calculating income taxes in interim periods. The standard also simplifies accounting for income taxes under U.S. GAAP by clarifying and amending existing guidance, including the recognition of deferred taxes for goodwill, the allocation of taxes to members of a consolidated group and requiring that an entity reflect the effect of enacted changes in tax laws or rates in the annual effective tax rate computation in the interim period that includes the enactment date. This guidance is effective for annual periods beginning after December 15, 2020, and interim periods thereafter; however, early adoption is permitted. The Company adopted this ASU as of January 1, 2021 and it has had no material impact on the condensed consolidated financial statements. Recently Issued Accounting Pronouncements Not Yet Adopted In February 2016, the Financial Accounting Standards Board, or the FASB, issued Accounting Standard Update, or ASU, No. 2016-02, (Topic 842) Leases, or ASU 2016-02. ASU 2016-02 requires an entity to recognize assets and liabilities arising from a lease for both financing and operating leases. The ASU will also require new qualitative and quantitative disclosures to help investors and other financial statement users better understand the amount, timing, and uncertainty of cash flows arising from leases. For public entities, ASU 2016-02 is effective for fiscal years beginning after December 15, 2018. As a result of the Company having elected the extended transition period for complying with new or revised accounting standards pursuant to Section 107(b) of the Jumpstart Our Business Startups Act of 2012, or the JOBS Act, ASU 2016-02 is effective for the Company for the year ended December 31, 2021, and all interim periods thereafter. Early adoption is permitted. In June 2020, the FASB issued 2020-05 which extended the adoption of ASU 2016-02 to the year ended December 31, 2022 and all interim periods thereafter. While early adoption is permitted, the Company intends to adopt for the year ended December 31, 2021, following the loss of Emerging Growth Company status effective January 01, 2022. In July 2018, the FASB issued ASU 2018-11 Leases – Targeted Improvements, or ASU 2018-11, intended to ease the implementation of the new lease standard for financial statement preparers by, among other things, allowing for an additional transition method. In lieu of presenting transition requirements to comparative periods, as previously required, an entity may now elect to show a cumulative effect adjustment on the date of adoption without the requirement to recast prior period financial statements or disclosures presented in accordance with ASU 2016-02. The Company is continuing to evaluate developments within the new lease guidance and is finalizing its evaluation of its existing population of contracts to ensure all contracts that meet the definition of a lease contract under the new standard are identified. The Company is currently evaluating the impact of adopting this guidance on the Company’s condensed consolidated financial statements and expects that its operating lease commitments will be subject to the new standard and recognized as right-of-use assets and operating lease liabilities upon adoption of this standard, which will increase the total assets and total liabilities that it reports relative to such amounts presented prior to adoption.

Summary of Significant Accoun_3

Summary of Significant Accounting Policies (Tables)	9 Months Ended
	Sep. 30, 2021
Accounting Policies [Abstract]
Schedule of Property, Plant and Equipment	Property and equipment are recorded at cost and depreciated using the straight-line method over the estimated useful lives of the respective assets, which are as follows: Estimated Useful Life Lab equipment 5 years Office equipment 3-5 years Furniture and fixtures 3 years Leasehold improvements Shorter of useful life or remaining lease term Property and equipment, net consisted of the following (in thousands): September 30, December 31, 2021 2020 Lab equipment $ 304 $ 130 Office equipment 313 260 Furniture and fixtures 37 37 Leasehold improvements 6 6 660 433 Less: accumulated depreciation (305) (188) $ 355 $ 245

Fair Value Measurements (Tables

Fair Value Measurements (Tables)	9 Months Ended
	Sep. 30, 2021
Fair Value Disclosures [Abstract]
Fair Value, Liabilities Measured on Recurring Basis, Unobservable Input Reconciliation	The following table provides a roll forward of the aggregate fair value of the Company’s convertible notes, for which fair value was determined using level 3 inputs (in thousands): Convertible notes Balance as of December 31, 2019 $ 21,089 Change in fair value 1,754 Settlement of convertible notes (21,614) Exchange difference (1,229) Balance as of September 30, 2020 $ —

Prepaid Expenses and Other Cu_2

Prepaid Expenses and Other Current Assets (Tables)	9 Months Ended
	Sep. 30, 2021
Deferred Costs, Capitalized, Prepaid, and Other Assets Disclosure [Abstract]
Prepaid Expenses and Other Current Assets	Prepaid expenses and other current assets consisted of the following (in thousands) : September 30, December 31, 2021 2020 UK R&D tax credit $ 6,664 $ 4,610 Prepaid insurance premium 4,469 3,154 Prepaid research and development 4,920 2,317 VAT recoverable 1,394 1,171 Deferred offering costs 228 — Other current assets 1,058 796 $ 18,733 $ 12,048

Property and Equipment, Net (Ta

Property and Equipment, Net (Tables)	9 Months Ended
	Sep. 30, 2021
Property, Plant and Equipment [Abstract]
Schedule of Property, Plant and Equipment	Property and equipment are recorded at cost and depreciated using the straight-line method over the estimated useful lives of the respective assets, which are as follows: Estimated Useful Life Lab equipment 5 years Office equipment 3-5 years Furniture and fixtures 3 years Leasehold improvements Shorter of useful life or remaining lease term Property and equipment, net consisted of the following (in thousands): September 30, December 31, 2021 2020 Lab equipment $ 304 $ 130 Office equipment 313 260 Furniture and fixtures 37 37 Leasehold improvements 6 6 660 433 Less: accumulated depreciation (305) (188) $ 355 $ 245

Accrued Expenses and Other Li_2

Accrued Expenses and Other Liabilities (Tables)	9 Months Ended
	Sep. 30, 2021
Other Liabilities Disclosure [Abstract]
Schedule of Accrued Expenses and Other Liabilities	Accrued expenses and other liabilities consisted of the following (in thousands) : September 30, December 31, 2021 2020 Accrued research and development expense $ 2,233 $ 720 Accrued professional expenses 768 701 Accrued compensation and benefit costs 2,026 1,687 Payroll tax payable 530 384 Income taxes payable 581 243 Other liabilities 443 413 $ 6,581 $ 4,148

Convertible Preferred Shares (T

Convertible Preferred Shares (Tables)	9 Months Ended
	Sep. 30, 2021
Debt Disclosure [Abstract]
Schedule of Preferred Shares and Series A Convertible Preferred Shares	Convertible preferred shares and Series A convertible preferred shares consisted of the following as of December 31, 2019 (in thousands, except for share amounts): Shares Liquidation Preference Carrying Value Authorized Outstanding Convertible preferred shares 2,650,980 2,650,980 $ 3,865 $ 3,761 Series A convertible preferred shares 7,131,525 7,131,525 35,414 35,147 9,782,505 9,782,505 $ 39,279 $ 38,908

Share-Based Compensation (Table

Share-Based Compensation (Tables)	9 Months Ended
	Sep. 30, 2021
Share-based Payment Arrangement [Abstract]
Schedule of Unvested Share Activity	A summary of the changes in the Company’s unvested ordinary shares during the nine months ended September 30, 2021 are as follows: Number of Shares Weighted Average Grant Date Fair Value Unvested and Outstanding as of December 31, 2020 13,757 $ 2.36 Granted — — Vested (13,757) 2.36 Forfeited — — Unvested and Outstanding as of September 30, 2021 — $ —
Schedule of Nonvested Restricted Share Units Activity	A summary of the changes in the Company’s unvested restricted share units during the nine months ended September 30, 2021 are as follows: Number of Shares Weighted Average Grant Date Fair Value Unvested and Outstanding as of December 31, 2020 217,482 $ 10.19 Granted — — Vested (56,887) 10.19 Forfeited — — Unvested and Outstanding as of September 30, 2021 160,595 $ 10.19
Schedule of Share-based Payment Arrangement, Option, Activity	The following table summarizes the Company’s share options activity for the nine months ended September 30, 2021 : Number of Shares Weighted Average Exercise Price Weighted Average Remaining Contractual Term (Years) Aggregate Intrinsic Value (in thousands) Outstanding as of December 31, 2020 4,430,340 $ 5.61 9.22 $ 186,426 Granted 752,702 $ 37.20 Exercised (1,015,915) $ 1.07 Forfeited (74,631) $ 9.11 Outstanding as of September 30, 2021 4,092,496 $ 12.18 8.79 $ 81,351 Exercisable as of September 30, 2021 2,294,380 $ 1.92 8.45 $ 64,148 Unvested as of September 30, 2021 1,798,116 $ 24.47 9.23 $ 17,203
Schedule of Valuation Assumptions	The weighted-average assumptions used in the Black-Scholes option pricing model to determine the fair value of the share options granted to employees and directors during the three months and nine months ended September 30, 2021 and 2020 were as follows: Three Months Ended September 30, Nine Months Ended September 30, 2021 2020 2021 2020 Expected term (in years) 6.07 Years 6.08 Years 6.07 Years 5.93 Years Expected volatility 66.90 % 66.90 % 67.20 % 66.00 % Risk-free interest rate 0.96 % 0.39 % 0.91 % 0.43 % Expected dividend yield — % — % — % — % Fair value of underlying ordinary shares $ 34.83 $ 17.00 $ 37.65 $ 10.30
Summary of Share-based Compensation Expense	Share-based compensation expense recorded as research and development and general and administrative expenses is as follows (in thousands): Three Months Ended September 30, Nine Months Ended September 30, 2021 2020 2021 2020 Research and development $ 1,288 $ 2,231 $ 3,023 $ 5,748 General and administrative 999 2,984 2,834 10,869 Total share-based compensation expense $ 2,287 $ 5,215 $ 5,857 $ 16,617

Net Loss Per Share (Tables)

Net Loss Per Share (Tables)	9 Months Ended
	Sep. 30, 2021
Earnings Per Share [Abstract]
Schedule of Earnings Per Share, Basic and Diluted	Basic and diluted net loss per share attributable to ordinary shareholders was calculated as follows (in thousands, except share and per share amounts): Three Months Ended September 30, Nine Months Ended September 30, 2021 2020 2021 2020 Numerator Net loss $ (15,849) $ (16,694) $ (46,092) $ (41,528) Net loss attributable to ordinary shareholders - basic and diluted $ (15,849) $ (16,694) $ (46,092) $ (41,528) Denominator Weighted-average number of ordinary shares used in net loss per share - basic and diluted 41,708,220 12,834,889 39,378,824 10,638,738 Net loss per share - basic and diluted $ (0.38) $ (1.30) $ (1.17) $ (3.90)
Schedule of Antidilutive Securities Excluded from Computation of Earnings Per Share	The Company excluded the following potential ordinary shares, presented based on amounts outstanding at each period end, from the computation of diluted net loss per share attributable to ordinary shareholders for the three months and nine months ended September 30, 2021 and 2020 because including them would have had an anti-dilutive effect: Three Months Ended September 30, Nine Months Ended September 30, 2021 2020 2021 2020 Unvested restricted shares — 22,011 — 22,011 Unvested restricted share units 160,595 257,708 160,595 257,708 Vested restricted share units, for which shares are not in issue 44,280 — 44,280 — Share options 4,092,496 4,482,507 4,092,496 4,482,507 4,297,371 4,762,226 4,297,371 4,762,226

Commitments and Contingencies (

Commitments and Contingencies (Tables)	9 Months Ended
	Sep. 30, 2021
Commitments and Contingencies Disclosure [Abstract]
Schedule of Future Minimum Lease Payments Due Under Operating Leases	The following table summarizes the future minimum lease payments due under operating leases as of September 30, 2021 (in thousands): Year end December, 31 Amount 2021 $ 751 2022 1,913 2023 1,222 $ 3,886

Nature of Business (Details)

Nature of Business (Details)	Oct. 08, 2021USD ($)shares	May 19, 2021shares	Sep. 22, 2020USD ($)shares	Aug. 07, 2020shares	Aug. 28, 2019USD ($)	May 31, 2021USD ($)	Sep. 30, 2021USD ($)shares	Jun. 30, 2021USD ($)	Mar. 31, 2021USD ($)	Sep. 30, 2020USD ($)	Jun. 30, 2020USD ($)	Mar. 31, 2020USD ($)	Sep. 30, 2021USD ($)shares	Sep. 30, 2020USD ($)	Sep. 30, 2021£ / shares	Jun. 30, 2021£ / shares	Mar. 31, 2021£ / shares	Dec. 31, 2020USD ($)shares	Dec. 31, 2020£ / shares	Sep. 30, 2020£ / shares	Sep. 22, 2020£ / sharesshares	Aug. 19, 2020£ / shares	Aug. 18, 2020£ / shares	Jun. 30, 2020£ / shares	Mar. 31, 2020£ / shares	Dec. 31, 2019£ / shares
Conversion of Stock [Line Items]
Shares issued, stock splits (in shares)				1,161
Stock split, conversion ratio			8.8028	0.00086133
Common stock, outstanding (in shares)																		35,930,331
Consideration received on transaction | $					$ 25,000,000	$ 154,800,000
Net loss | $							$ 15,849,000	$ 17,528,000	$ 12,715,000	$ 16,694,000	$ 16,249,000	$ 8,585,000	$ 46,092,000	$ 41,528,000
Accumulated deficit | $							143,991,000						143,991,000					$ 97,899,000
Cash and cash equivalents | $							$ 293,959,000			$ 196,505,000			$ 293,959,000	$ 196,505,000				$ 190,327,000
IPO
Conversion of Stock [Line Items]
Consideration received on transaction | $			$ 132,800,000
Ordinary Shares
Conversion of Stock [Line Items]
Common stock, par value (in dollars per share) | £ / shares															£ 0.008	£ 0.008	£ 0.008		£ 0.008	£ 0.008	£ 0.008	£ 0.001	£ 1	£ 0.008	£ 0.008	£ 0.008
Common stock, outstanding (in shares)							41,731,180						41,731,180								27,305,331
Ordinary Shares | Over-Allotment Option
Conversion of Stock [Line Items]
Sale of stock, shares issued in transaction (in shares)		600,000
Deferred Shares
Conversion of Stock [Line Items]
Common stock, par value (in dollars per share) | £ / shares															£ 21,921.504	£ 21,921.504	£ 21,921.504		£ 21,921.504	£ 21,921.504	£ 21,921.504			£ 21,921.504	£ 21,921.504	£ 21,921.504
Common stock, outstanding (in shares)							1						1					1
American Depositary Shares | Cowen And Company, LLC | Subsequent Event | Forecast
Conversion of Stock [Line Items]
Consideration received on transaction | $	$ 150,000,000
Sale of Stock, Exchange Rate To Shares	1
American Depositary Shares | IPO
Conversion of Stock [Line Items]
Sale of stock, shares issued in transaction (in shares)			8,625,000
Sale of stock, price per share (in dollars per share) | £ / shares																					£ 17
American Depositary Shares | Over-Allotment Option
Conversion of Stock [Line Items]
Sale of stock, shares issued in transaction (in shares)			1,125,000

Summary of Significant Accoun_4

Summary of Significant Accounting Policies - Narrative (Details) € in Millions, £ in Millions, $ in Millions	Apr. 17, 2020USD ($)	Aug. 28, 2019USD ($)	May 31, 2021USD ($)	Sep. 30, 2021geographicRegion	Sep. 30, 2020	Sep. 30, 2021GBP (£)geographicRegion	Sep. 30, 2021EUR (€)geographicRegion	Sep. 30, 2020	Apr. 17, 2020GBP (£)	Aug. 28, 2019GBP (£)
New Accounting Pronouncements or Change in Accounting Principle [Line Items]
Consideration received on transaction		$ 25	$ 154.8
Number of geographic regions | geographicRegion				2		2	2
Expected dividend yield				0.00%	0.00%	0.00%	0.00%	0.00%
Likelihood of benefit being realized percent						50.00%	50.00%
Convertible Debt
New Accounting Pronouncements or Change in Accounting Principle [Line Items]
Convertible loan notes	$ 18.4	$ 18.4							£ 15	£ 15
Convertible B preferred stock
New Accounting Pronouncements or Change in Accounting Principle [Line Items]
Additional funding	$ 80
United Kingdom Research and Development Tax Credit Regime, Small or Medium-Sized Enterprises (SME)
New Accounting Pronouncements or Change in Accounting Principle [Line Items]
Cash rebate percent						33.35%	33.35%
Total aid claimable | €							€ 7.5
United Kingdom Research and Development Tax Credit Regime
New Accounting Pronouncements or Change in Accounting Principle [Line Items]
Cash rebate percent						21.67%	21.67%
Annual offset amount | £						£ 5
Percentage of taxable profits						50.00%	50.00%

Summary of Significant Accoun_5

Summary of Significant Accounting Policies - Property, Plant and Equipment (Details)	9 Months Ended
	Sep. 30, 2021
Lab equipment
Property, Plant and Equipment [Line Items]
Useful life	5 years
Office equipment | Minimum
Property, Plant and Equipment [Line Items]
Useful life	3 years
Office equipment | Maximum
Property, Plant and Equipment [Line Items]
Useful life	5 years
Furniture and fixtures
Property, Plant and Equipment [Line Items]
Useful life	3 years

Fair Value Measurements - Narra

Fair Value Measurements - Narrative (Details) - USD ($) $ in Thousands	9 Months Ended
	Sep. 30, 2021	Sep. 30, 2020
Fair Value Disclosures [Abstract]
Fair value change of convertible notes	$ 0	$ 1,754

Fair Value Measurements - Fair

Fair Value Measurements - Fair Value, Liabilities Measured on Recurring Basis, Unobservable Input Reconciliation (Details) - Convertible Debt $ in Thousands	9 Months Ended
	Sep. 30, 2020USD ($)
Fair Value, Liabilities Measured on Recurring Basis, Unobservable Input Reconciliation, Calculation [Roll Forward]
Convertible notes, fair value, beginning balance	$ 21,089
Change in fair value	1,754
Settlement of convertible notes	(21,614)
Exchange difference	(1,229)
Convertible notes, fair value, ending balance	$ 0

Investment - Narrative (Details

Investment - Narrative (Details) - USD ($) $ in Thousands	Mar. 06, 2020	Sep. 30, 2021	Sep. 30, 2020
Schedule of Equity Method Investments [Line Items]
Purchase of investments		$ 0	$ 492
Delix Therapeutics, Inc.
Schedule of Equity Method Investments [Line Items]
Ownership percentage in Delix Therapeutics, Inc	8.00%
Delix Therapeutics, Inc.
Schedule of Equity Method Investments [Line Items]
Purchase of investments	$ 500

Prepaid Expenses and Other Cu_3

Prepaid Expenses and Other Current Assets (Details) - USD ($) $ in Thousands	Sep. 30, 2021	Dec. 31, 2020
Deferred Costs, Capitalized, Prepaid, and Other Assets Disclosure [Abstract]
UK R&D tax credit	$ 6,664	$ 4,610
Prepaid insurance premium	4,469	3,154
Prepaid research and development	4,920	2,317
VAT recoverable	1,394	1,171
Deferred offering costs	228	0
Deferred offering costs	1,058	796
Prepaid expenses and other current assets	$ 18,733	$ 12,048

Property and Equipment, Net (De

Property and Equipment, Net (Details) - USD ($) $ in Thousands	3 Months Ended		9 Months Ended
	Sep. 30, 2021	Sep. 30, 2020	Sep. 30, 2021	Sep. 30, 2020	Dec. 31, 2020
Property, Plant and Equipment [Line Items]
Property and equipment, gross	$ 660		$ 660		$ 433
Less: accumulated depreciation	(305)		(305)		(188)
Investment	355		355		245
Depreciation and amortization	100	$ 100	123	$ 84
Lab equipment
Property, Plant and Equipment [Line Items]
Property and equipment, gross	304		304		130
Office equipment
Property, Plant and Equipment [Line Items]
Property and equipment, gross	313		313		260
Furniture and fixtures
Property, Plant and Equipment [Line Items]
Property and equipment, gross	37		37		37
Leasehold improvements
Property, Plant and Equipment [Line Items]
Property and equipment, gross	$ 6		$ 6		$ 6

Accrued Expenses and Other Li_3

Accrued Expenses and Other Liabilities (Details) - USD ($) $ in Thousands	Sep. 30, 2021	Dec. 31, 2020
Other Liabilities Disclosure [Abstract]
Accrued research and development expense	$ 2,233	$ 720
Accrued professional expenses	768	701
Accrued compensation and benefit costs	2,026	1,687
Payroll tax payable	530	384
Income taxes payable	581	243
Other liabilities	443	413
Total accrued expenses and other liabilities	$ 6,581	$ 4,148

Convertible Notes - Narrative (

Convertible Notes - Narrative (Details) $ in Thousands, £ in Millions	Apr. 17, 2020USD ($)shares	Jun. 30, 2020shares	Sep. 30, 2021USD ($)	Sep. 30, 2020USD ($)	Apr. 17, 2020GBP (£)	Aug. 28, 2019USD ($)	Aug. 28, 2019GBP (£)
Debt Instrument, Redemption [Line Items]
Fair value change of convertible notes | $			$ 0	$ 1,754
Convertible B preferred stock
Debt Instrument, Redemption [Line Items]
Conversion of notes into B convertible preferred shares (in shares) | shares	1,723,263	1,723,263
Convertible Debt
Debt Instrument, Redemption [Line Items]
Convertible notes, face amount	$ 18,400				£ 15	$ 18,400	£ 15
Convertible notes payable
Debt Instrument, Redemption [Line Items]
Convertible notes interest (in percentage)						3.00%	3.00%
Convertible notes, discount of per share price (in percentage)						15.00%	15.00%

Convertible Preferred Shares -

Convertible Preferred Shares - Narrative (Details) - USD ($) $ / shares in Units, $ in Millions	Sep. 22, 2020	Apr. 17, 2020	Aug. 31, 2021	Sep. 30, 2018	Aug. 31, 2017	Sep. 30, 2020	Jun. 30, 2020
Share options
Debt Instrument, Redemption [Line Items]
Convertible preferred shares issued (in shares)					2,650,980	2,650,980
Proceeds from Issuance of Convertible Preferred Stock					$ 3.9
Preferred shares issuance costs					$ 0.1
Convertible A preferred stock
Debt Instrument, Redemption [Line Items]
Convertible preferred shares issued (in shares)				7,131,525		7,131,525
Proceeds from Issuance of Convertible Preferred Stock				$ 35.4
Preferred shares issuance costs				$ 0.3
Convertible B preferred stock
Debt Instrument, Redemption [Line Items]
Convertible preferred shares issued (in shares)						6,636,667
Proceeds from Issuance of Convertible Preferred Stock		$ 56.3	$ 5.3
Preferred shares issuance costs		0.3
Proceeds from Issuance of Debt		$ 80
Convertible preferred shares (in shares)		4,487,533	425,871
Conversion of notes into B convertible preferred shares (in shares)		1,723,263					1,723,263
Issuance price of Series B convertible preferred shares (in dollars per share)		$ 1.42
Ordinary Shares | Common Stock
Debt Instrument, Redemption [Line Items]
Convertible preferred shares issued (in shares)	16,419,172					16,419,172

Convertible Preferred Shares _2

Convertible Preferred Shares - Schedule of preferred shares and Series A convertible preferred shares (Details) - USD ($) $ in Thousands	Sep. 30, 2021	Sep. 30, 2020	Jun. 30, 2020	Mar. 31, 2020	Dec. 31, 2019
Debt Instrument, Redemption [Line Items]
Convertible preferred shares authorized (in shares)					9,782,505
Convertible preferred shares outstanding (in shares)					9,782,505
Liquidation Preference					$ 39,279
Carrying Value					$ 38,908
Share options
Debt Instrument, Redemption [Line Items]
Convertible preferred shares authorized (in shares)					2,650,980
Convertible preferred shares outstanding (in shares)	0	0	2,650,980	2,650,980	2,650,980
Liquidation Preference					$ 3,865
Carrying Value	$ 0	$ 0	$ 3,761	$ 3,761	$ 3,761
Convertible A preferred stock
Debt Instrument, Redemption [Line Items]
Convertible preferred shares authorized (in shares)					7,131,525
Convertible preferred shares outstanding (in shares)	0	0	7,131,525	7,131,525	7,131,525
Liquidation Preference					$ 35,414
Carrying Value	$ 0	$ 0	$ 35,147	$ 35,147	$ 35,147

Ordinary Shares - Narrative (De

Ordinary Shares - Narrative (Details) $ in Millions

May 19, 2021shares

May 04, 2021shares

Sep. 22, 2020USD ($)shares

Aug. 28, 2019USD ($)

Aug. 17, 2018

Aug. 17, 2017

Aug. 31, 2021shares

May 31, 2021USD ($)shares

May 19, 2021USD ($)

Jul. 31, 2020shares

Oct. 31, 2019shares

Aug. 31, 2017shares

Sep. 30, 2021vote£ / sharesshares

Jun. 30, 2021£ / sharesshares

Mar. 31, 2021£ / sharesshares

Sep. 30, 2020£ / sharesshares

Sep. 30, 2021vote£ / sharesshares

Aug. 17, 2020installment

Dec. 31, 2020£ / shares

Sep. 22, 2020£ / shares

Aug. 19, 2020£ / shares

Aug. 18, 2020£ / shares

Jun. 30, 2020£ / shares

Mar. 31, 2020£ / shares

Dec. 31, 2019£ / shares

Class of Stock [Line Items]

Consideration received on transaction | $

$ 25

$ 154.8

Number of votes | vote

1

1

Exercise of share options (in shares)

1,015,915

IPO

Class of Stock [Line Items]

Consideration received on transaction | $

$ 132.8

Follow-on Offering

Class of Stock [Line Items]

Consideration received on transaction | $

$ 154.8

Ordinary Shares

Class of Stock [Line Items]

Common stock, issued for services (in shares)

10,551,166

Common stock, par value (in dollars per share) | £ / shares

£ 0.008

£ 0.008

£ 0.008

£ 0.008

£ 0.008

£ 0.008

£ 0.008

£ 0.001

£ 1

£ 0.008

£ 0.008

£ 0.008

Number of monthly installments | installment

24

Issuance of shares (in shares)

0

0

1,188,242

Forfeiture of ordinary shares (in shares)

63,972

Ordinary Shares | Nonemployee

Class of Stock [Line Items]

Issuance of shares (in shares)

102,214

Award vesting period

3 years

Ordinary Shares | Employee

Class of Stock [Line Items]

Issuance of shares (in shares)

99,049

Award vesting period

4 years

Ordinary Shares | Follow-on Offering

Class of Stock [Line Items]

Sale of stock, shares issued in transaction (in shares)

4,000,000

Ordinary Shares | Over-Allotment Option

Class of Stock [Line Items]

Sale of stock, shares issued in transaction (in shares)

600,000

Ordinary Shares | Common Stock

Class of Stock [Line Items]

Issuance of shares (in shares)

4,600,000

Forfeiture of ordinary shares (in shares)

63,972

Convertible preferred shares issued (in shares)

16,419,172

16,419,172

Exercise of share options (in shares)

23,238

351,449

581,328

197,702

Ordinary Shares | Common Stock | Options Granted In Previous Year

Class of Stock [Line Items]

Exercise of share options (in shares)

232,227

232,227

59,900

Ordinary Shares | Common Stock | IPO

Class of Stock [Line Items]

Issuance of shares (in shares)

8,625,000

Ordinary Shares | Share-based Payment Arrangement, Tranche One

Class of Stock [Line Items]

Award vesting percentage

25.00%

Ordinary Shares | Share-based Payment Arrangement, Tranche Two

Class of Stock [Line Items]

Award vesting percentage

25.00%

Ordinary Shares | Share-based Payment Arrangement, Tranche Three

Class of Stock [Line Items]

Award vesting percentage

50.00%

American Depositary Shares | IPO

Class of Stock [Line Items]

Sale of stock, shares issued in transaction (in shares)

8,625,000

Sale of stock, price per share (in dollars per share) | £ / shares

£ 17

American Depositary Shares | Over-Allotment Option

Class of Stock [Line Items]

Sale of stock, shares issued in transaction (in shares)

1,125,000

Share-Based Compensation - Narr

Share-Based Compensation - Narrative (Details) $ / shares in Units, $ in Thousands

Aug. 13, 2021shares

May 19, 2020shares

Aug. 17, 2018

Aug. 17, 2017

Aug. 31, 2021shares

May 31, 2021shares

Sep. 30, 2021USD ($)shares

Sep. 30, 2020USD ($)shares

Sep. 30, 2021USD ($)day$ / sharesshares

Sep. 30, 2021USD ($)£ / sharesshares

Sep. 30, 2020USD ($)period$ / sharesshares

Dec. 31, 2020

Aug. 17, 2020

Share-based Compensation Arrangement by Share-based Payment Award [Line Items]

Vested (in shares)

12,607

Share-based compensation expense | $

$ 2,287

$ 5,215

$ 5,857

$ 16,617

Number of periods | period

11

Granted (in dollars per share) | $ / shares

$ 22.71

$ 8.25

Unrecognized compensation cost of options | $

27,600

$ 27,600

$ 27,600

Weighted average grant date fair value of shares granted (in dollars per share) | $ / shares

$ 22.71

$ 8.25

Research and Development Expense

Share-based Compensation Arrangement by Share-based Payment Award [Line Items]

Share-based compensation expense | $

1,288

2,231

$ 3,023

$ 5,748

General and Administrative Expense

Share-based Compensation Arrangement by Share-based Payment Award [Line Items]

Share-based compensation expense | $

999

$ 2,984

$ 2,834

$ 10,869

United Kingdom Employee

Share-based Compensation Arrangement by Share-based Payment Award [Line Items]

Period for recognition

3 years 2 months 12 days

Weighted average exercise price (in dollars per share) | $ / shares

$ 4

United States Employee

Share-based Compensation Arrangement by Share-based Payment Award [Line Items]

Weighted average exercise price (in dollars per share) | $ / shares

$ 4.72

Share-based Payment Arrangement, Tranche One | Ordinary Shares

Share-based Compensation Arrangement by Share-based Payment Award [Line Items]

Award vesting percentage

25.00%

Share-based Payment Arrangement, Tranche Two | Ordinary Shares

Share-based Compensation Arrangement by Share-based Payment Award [Line Items]

Award vesting percentage

25.00%

Share-based Payment Arrangement, Tranche Three | Ordinary Shares

Share-based Compensation Arrangement by Share-based Payment Award [Line Items]

Award vesting percentage

50.00%

Ordinary Shares

Share-based Compensation Arrangement by Share-based Payment Award [Line Items]

Vested (in shares)

12,607

Granted (in shares)

0

Granted (in dollars per share) | $ / shares

$ 0

Weighted average grant date fair value of shares granted (in dollars per share) | $ / shares

$ 0

Share options | Research and Development Expense

Share-based Compensation Arrangement by Share-based Payment Award [Line Items]

Share-based compensation expense | $

$ 2,400

Share options | General and Administrative Expense

Share-based Compensation Arrangement by Share-based Payment Award [Line Items]

Share-based compensation expense | $

7,000

Vested restricted share units, for which shares are not in issue

Share-based Compensation Arrangement by Share-based Payment Award [Line Items]

Vested (in shares)

12,607

44,280

44,280

56,887

Vested in period, fair value | $

$ 100

$ 1,200

Unrecognized compensation cost | $

$ 1,600

$ 1,600

$ 1,600

Period for recognition

2 years 9 months 18 days

Exercise price (in pound sterling per share) | £ / shares

$ 0.01

2017 Equity Incentive Plan | President and Chief Business Officer

Share-based Compensation Arrangement by Share-based Payment Award [Line Items]

Granted (in shares)

1,015,813

2017 Equity Incentive Plan | Ordinary Shares

Share-based Compensation Arrangement by Share-based Payment Award [Line Items]

Number of shares authorized

13,601,246

13,601,246

13,601,246

Number of shares available for issuance

445,943

445,943

445,943

Vested (in shares)

12,607

2017 Equity Incentive Plan | Share options

Share-based Compensation Arrangement by Share-based Payment Award [Line Items]

Award vesting period

3 years

Share-based compensation expense | $

$ 9,400

Expiration period

10 years

2017 Equity Incentive Plan | Share options | Share-based Payment Arrangement, Tranche One

Share-based Compensation Arrangement by Share-based Payment Award [Line Items]

Award vesting percentage

33.30%

2017 Equity Incentive Plan | Share options | Share-based Payment Arrangement, Tranche Two

Share-based Compensation Arrangement by Share-based Payment Award [Line Items]

Award vesting percentage

25.00%

2017 Equity Incentive Plan | Share options | Share-based Payment Arrangement, Tranche Three

Share-based Compensation Arrangement by Share-based Payment Award [Line Items]

Award vesting percentage

75.00%

2017 Equity Incentive Plan | Share options | Minimum

Share-based Compensation Arrangement by Share-based Payment Award [Line Items]

Award vesting period

3 years

2017 Equity Incentive Plan | Share options | Maximum

Share-based Compensation Arrangement by Share-based Payment Award [Line Items]

Award vesting period

4 years

2017 Equity Incentive Plan | Vested restricted share units, for which shares are not in issue

Share-based Compensation Arrangement by Share-based Payment Award [Line Items]

Vested (in shares)

56,887

Award vesting period

4 years

Award vesting percentage

25.00%

2017 Equity Incentive Plan | Vested restricted share units, for which shares are not in issue | Share-based Payment Arrangement, Tranche One

Share-based Compensation Arrangement by Share-based Payment Award [Line Items]

Award vesting percentage

25.00%

Percentage amount closing price is higher than listing price

20.00%

Threshold consecutive trading days | day

5

2017 Equity Incentive Plan | Vested restricted share units, for which shares are not in issue | Share-Based Payment Arrangement, Tranche Four

Share-based Compensation Arrangement by Share-based Payment Award [Line Items]

Award vesting percentage

6.25%

2020 Share Option Plan | Ordinary Shares

Share-based Compensation Arrangement by Share-based Payment Award [Line Items]

Shares reserved for future issuance (in shares)

2,074,325

2,074,325

2,074,325

2,074,325

2,074,325

Maximum percentage of shares outstanding number of shares reserved for issuance may increase

4.00%

4.00%

Number of shares available for grant

494,809

494,809

494,809

Share-Based Compensation - Sche

Share-Based Compensation - Schedule of Unvested Share Activity (Details) - $ / shares	9 Months Ended
	Sep. 30, 2021	Sep. 30, 2020
Weighted Average Grant Date Fair Value
Granted (in dollars per share)	$ 22.71	$ 8.25
Ordinary Shares
Number of Shares
Unvested and Outstanding, beginning balance (in shares)	13,757
Granted (in shares)	0
Vested (in shares)	(13,757)
Forfeited (in shares)	0
Unvested and Outstanding, ending balance (in shares)	0
Weighted Average Grant Date Fair Value
Weighted Average Grant Date Fair Value, beginning balance (in dollars per share)	$ 2.36
Granted (in dollars per share)	0
Vested (in dollars per share)	2.36
Forfeited (in dollars per share)	0
Weighted Average Grant Date Fair Value, ending balance (in dollars per share)	$ 0

Share-Based Compensation - Sc_2

Share-Based Compensation - Schedule of Nonvested Restricted Share Units Activity (Details) - $ / shares	Aug. 13, 2021	Aug. 31, 2021	May 31, 2021	Sep. 30, 2021	Dec. 31, 2020
Number of Shares
Vested (in shares)				12,607
Vested restricted share units, for which shares are not in issue
Number of Shares
Unvested and Outstanding, beginning balance (in shares)				160,595	217,482
Granted (in shares)				0
Vested (in shares)	12,607	44,280	44,280	56,887
Forfeited (in shares)				0
Unvested and Outstanding, ending balance (in shares)				160,595
Weighted Average Grant Date Fair Value
Weighted Average Grant Date Fair Value, beginning balance (in dollars per share)				$ 10.19	$ 10.19
Granted (in dollars per share)				0
Vested (in dollars per share)				10.19
Forfeited (in dollars per share)				0
Weighted Average Grant Date Fair Value, ending balance (in dollars per share)				$ 10.19

Share-Based Compensation - Sc_3

Share-Based Compensation - Schedule of Share-based Payment Arrangement, Option, Activity (Details) - USD ($) $ / shares in Units, $ in Thousands	3 Months Ended	9 Months Ended
	Mar. 31, 2021	Sep. 30, 2021	Dec. 31, 2020
Number of Shares
Outstanding, beginning balance (in shares)		4,092,496	4,430,340
Granted (in shares)		752,702
Exercised (in shares)		(1,015,915)
Forfeited (in shares)		(74,631)
Outstanding, ending balance (in shares)		4,092,496
Weighted Average Exercise Price
Outstanding, Weighted Average Exercise Price, beginning balance (in dollars per share)		$ 12.18	$ 5.61
Granted (in dollars per share)		37.20
Exercised (in dollars per share)		1.07
Forfeited (in dollars per share)		9.11
Outstanding, Weighted Average Exercise Price, ending balance (in dollars per share)		$ 12.18
Weighted Average Remaining Contractual Term (Years)	9 years 2 months 19 days	8 years 9 months 14 days
Aggregate Intrinsic Value		$ 81,351	$ 186,426
Exercisable as of June 30, 2021 (in shares)		2,294,380
Exercisable, Weighted Average Exercise Price (in dollars per share)		$ 1.92
Exercisable, Weighted Average Remaining Contractual Term		8 years 5 months 12 days
Exercisable, Aggregate Intrinsic Value		$ 64,148
Unvested as of June 30, 2021 (in shares)		1,798,116
Unvested, Weighted Average Exercise Price (in dollars per share)		$ 24.47
Unvested, Weighted Average Remaining Contractual Term		9 years 2 months 23 days
Unvested, Aggregate Intrinsic Value		$ 17,203

Share-Based Compensation - Sc_4

Share-Based Compensation - Schedule of Valuation Assumptions (Details) - $ / shares	3 Months Ended		9 Months Ended
	Sep. 30, 2021	Sep. 30, 2020	Sep. 30, 2021	Sep. 30, 2020
Share-based Payment Arrangement [Abstract]
Expected term (in years)	6 years 25 days	6 years 29 days	6 years 25 days	5 years 11 months 4 days
Expected volatility	66.90%	66.90%	67.20%	66.00%
Risk-free interest rate	0.96%	0.39%	0.91%	0.43%
Expected dividend yield	0.00%	0.00%	0.00%	0.00%
Fair value of underlying ordinary shares (in shares)	$ 34.83	$ 17	$ 37.65	$ 10.30

Share-Based Compensation - Summ

Share-Based Compensation - Summary of Share-based Compensation Expense (Details) - USD ($) $ in Thousands	3 Months Ended		9 Months Ended
	Sep. 30, 2021	Sep. 30, 2020	Sep. 30, 2021	Sep. 30, 2020
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Share-based compensation expense	$ 2,287	$ 5,215	$ 5,857	$ 16,617
Research and Development Expense
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Share-based compensation expense	1,288	2,231	3,023	5,748
General and Administrative Expense
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Share-based compensation expense	$ 999	$ 2,984	$ 2,834	$ 10,869

Net Loss Per Share - Schedule o

Net Loss Per Share - Schedule of Earnings Per Share, Basic and Diluted (Details) - USD ($) $ / shares in Units, $ in Thousands	3 Months Ended						9 Months Ended
	Sep. 30, 2021	Jun. 30, 2021	Mar. 31, 2021	Sep. 30, 2020	Jun. 30, 2020	Mar. 31, 2020	Sep. 30, 2021	Sep. 30, 2020
Earnings Per Share [Abstract]
Net loss	$ (15,849)	$ (17,528)	$ (12,715)	$ (16,694)	$ (16,249)	$ (8,585)	$ (46,092)	$ (41,528)
Net loss attributable to ordinary shareholders - basic	(15,849)			(16,694)			(46,092)	(41,528)
Net loss attributable to ordinary shareholders - diluted	$ (15,849)			$ (16,694)			$ (46,092)	$ (41,528)
Weighted-average number of ordinary shares used in net loss per share - basic (in shares)	41,708,220			12,834,889			39,378,824	10,638,738
Weighted-average number of ordinary shares used in net loss per share - diluted (in shares)	41,708,220			12,834,889			39,378,824	10,638,738
Net loss attributable to ordinary shareholders - basic (in dollars per share)	$ (0.38)			$ (1.30)			$ (1.17)	$ (3.90)
Net loss attributable to ordinary shareholders - diluted (in dollars per share)	$ (0.38)			$ (1.30)			$ (1.17)	$ (3.90)

Net Loss Per Share - Schedule_2

Net Loss Per Share - Schedule of Antidilutive Securities Excluded from Computation of Earnings Per Share (Details) - shares	3 Months Ended		9 Months Ended
	Sep. 30, 2021	Sep. 30, 2020	Sep. 30, 2021	Sep. 30, 2020
Antidilutive Securities Excluded from Computation of Earnings Per Share [Line Items]
Antidilutive securities excluded from computation of earnings per share	4,297,371	4,762,226	4,297,371	4,762,226
Unvested restricted shares
Antidilutive Securities Excluded from Computation of Earnings Per Share [Line Items]
Antidilutive securities excluded from computation of earnings per share	0	22,011	0	22,011
Unvested restricted share units
Antidilutive Securities Excluded from Computation of Earnings Per Share [Line Items]
Antidilutive securities excluded from computation of earnings per share	160,595	257,708	160,595	257,708
Vested restricted share units, for which shares are not in issue
Antidilutive Securities Excluded from Computation of Earnings Per Share [Line Items]
Antidilutive securities excluded from computation of earnings per share	44,280	0	44,280	0
Share options
Antidilutive Securities Excluded from Computation of Earnings Per Share [Line Items]
Antidilutive securities excluded from computation of earnings per share	4,092,496	4,482,507	4,092,496	4,482,507

Commitments and Contingencies -

Commitments and Contingencies - Narrative (Details) - USD ($) $ in Millions	9 Months Ended
	Sep. 30, 2021	Sep. 30, 2020	Jul. 09, 2021
Commitments and Contingencies Disclosure [Abstract]
Lease term	2 years		2 years
Operating leases, rent expense	$ 1.1	$ 0.8

Commitments and Contingencies_2

Commitments and Contingencies - Schedule of operating leases (Details) $ in Thousands	Sep. 30, 2021USD ($)
Commitments and Contingencies Disclosure [Abstract]
2021	$ 751
2022	1,913
2023	1,222
Total of operating leases to be paid	$ 3,886

Related Party Transactions (Det

Related Party Transactions (Details) - Tapestry Networks, Inc. - USD ($) $ in Millions	3 Months Ended		9 Months Ended
	Sep. 30, 2021	Sep. 30, 2020	Sep. 30, 2021	Sep. 30, 2020
Related Party Transaction [Line Items]
Due to related parties	$ 0.1	$ 0.1	$ 0.1	$ 0.1
Professional Fees
Related Party Transaction [Line Items]
Expenses from transactions with related party	$ 0.1	$ 0.1	$ 0.1	$ 0.1

Employee Benefit Plans (Details

Employee Benefit Plans (Details) - USD ($) $ in Millions	9 Months Ended
	Sep. 30, 2021	Sep. 30, 2020
Retirement Benefits [Abstract]
Company contributions on behalf of the employee	$ 0.2	$ 0.1

Subsequent Events (Details)

Subsequent Events (Details) - Subsequent Event	Nov. 09, 2021pValuenumberOfParticipantg	Nov. 03, 2021numberOfParticipant	Oct. 01, 2021shares
Subsequent Event [Line Items]
Number of participants enrolled in PTSD study		20
COMP360 S study, number of participants	233
COMP360 study, dose weight | g	0.025
COMP360 study, p-value | pValue	0.001
Employee Stock Purchase Plan | Ordinary Shares
Subsequent Event [Line Items]
Shares reserved for future issuance (in shares) | shares			340,053