| Document And Entity Information | Feb. 11, 2021 |
| Document Information [Line Items] | |
| Entity, Registrant Name | ACELRX PHARMACEUTICALS, INC. |
| Document, Type | 8-K |
| Document, Period End Date | Feb. 11, 2021 |
| Entity, Incorporation, State or Country Code | DE |
| Entity, File Number | 001-35068 |
| Entity, Tax Identification Number | 41-2193603 |
| Entity, Address, Address Line One | 351 Galveston Drive |
| Entity, Address, City or Town | Redwood City |
| Entity, Address, State or Province | CA |
| Entity, Address, Postal Zip Code | 94063 |
| City Area Code | 650 |
| Local Phone Number | 216-3500 |
| Written Communications | false |
| Soliciting Material | false |
| Pre-commencement Tender Offer | false |
| Pre-commencement Issuer Tender Offer | false |
| Title of 12(b) Security | Common Stock |
| Trading Symbol | ACRX |
| Security Exchange Name | NASDAQ |
| Entity, Emerging Growth Company | false |
| Amendment Flag | false |
| Entity, Central Index Key | 0001427925 |
