| Document And Entity Information - USD ($) | Dec. 31, 2021 | Dec. 31, 2020 | Mar. 31, 2022 | Jun. 30, 2021 |
| Document Information [Line Items] | ||||
| Entity, Registrant Name | ACELRX PHARMACEUTICALS, INC. | |||
| Document, Type | 10-K/A | |||
| Document, Annual Report | true | |||
| Document, Period End Date | Dec. 31, 2021 | |||
| Current Fiscal Year End Date | --12-31 | |||
| Document, Fiscal Period Focus | FY | |||
| Document, Fiscal Year Focus | 2021 | |||
| Document, Transition Report | false | |||
| Entity, File Number | 001-35068 | |||
| Entity, Incorporation, State or Country Code | DE | |||
| Entity, Tax Identification Number | 41-2193603 | |||
| Entity, Address, Address Line One | 25821 Industrial Boulevard, Suite 400 | |||
| Entity, Address, City or Town | Hayward | |||
| Entity, Address, State or Province | CA | |||
| Entity, Address, Postal Zip Code | 94545 | |||
| City Area Code | 650 | |||
| Local Phone Number | 216-3500 | |||
| Title of 12(b) Security | Common Stock | |||
| Trading Symbol | ACRX | |||
| Security Exchange Name | NASDAQ | |||
| Entity, Well-known Seasoned Issuer | No | |||
| Entity, Voluntary Filers | No | |||
| Entity, Current Reporting Status | Yes | |||
| Entity, Interactive Data, Current | Yes | |||
| Entity, Filer Category | Non-accelerated Filer | |||
| Entity, Small Business | true | |||
| Entity, Emerging Growth Company | false | |||
| ICFR Auditor Attestation Flag | false | |||
| Entity, Shell Company | false | |||
| Entity, Public Float | $ 161,163,094 | |||
| Entity, Common Stock Shares, Outstanding | 146,949,320 | |||
| Amendment Description | On March 10, 2022, AcelRx, Inc, filed its Annual Report on Form 10-K for the year ended December 31, 2021, or the 2021 Annual Report. The 2021 Annual Report omitted Part III, Items 10 (Directors, Executive Officers and Corporate Governance), 11 (Executive Compensation), 12 (Security Ownership of Certain Beneficial Owners and Management and Related Stockholder Matters), 13 (Certain Relationships and Related Transactions, and Director Independence) and 14 (Principal Accountant Fees and Services) in reliance on General Instruction G(3) to Form 10-K, which provides that such information may be either incorporated by reference from the registrant’s definitive proxy statement or included in an amendment to Form 10-K, in either case filed with the Securities and Exchange Commission, or the SEC, not later than 120 days after the end of the fiscal year. We currently expect that our definitive proxy statement for our 2022 annual meeting of stockholders will be filed later than the 120th day after the end of the last fiscal year. Accordingly, this Amendment No. 1 to Form 10-K, or this Amendment, is being filed solely to: ● amend Part III, Items 10, 11, 12, 13 and 14 of the 2021 Annual Report to include the information required by such items; ● delete the reference on the cover of the 2021 Annual Report to the incorporation by reference of portions of our proxy statement into Part III of the 2021 Annual Report; and ● file new certifications of our principal executive officer and principal financial officer as exhibits to this Amendment under Item 15 of Part IV hereof, pursuant to Rule 12b-15 under the Securities Exchange Act of 1934. Because no financial statements have been included in this Amendment and this Amendment does not contain or amend any disclosure with respect to Items 307 and 308 of Regulation S-K, paragraphs 3, 4 and 5 of the certifications have been omitted. We are not including the certifications under Section 906 of the Sarbanes-Oxley Act of 2002 as no financial statements are being filed with this Amendment. Except as described above, this Amendment does not modify or update disclosure in, or exhibits to, the 2021 Annual Report. Furthermore, this Amendment does not change any previously reported financial results, nor does it reflect events occurring after the date of the 2021 Annual Report. Information not affected by this Amendment remains unchanged and reflects the disclosures made at the time the 2021 Annual Report was filed. Accordingly, this Amendment should be read in conjunction with the 2021 Annual Report and our other filings with the SEC. | |||
| Auditor Name | WithumSmith+Brown | OUM & Co. LLP | ||
| Auditor Firm ID | 100 | 252 | ||
| Auditor Location | San Francisco, CA | San Francisco, CA | ||
| Amendment Flag | true | |||
| Entity, Central Index Key | 0001427925 |
