Document And Entity Information - USD ($)
 12 Months Ended
Dec. 31, 2021
Mar. 07, 2022
Jun. 30, 2021
Document Information [Line Items]      
Entity Central Index Key 0001427925    
Entity Registrant Name ACELRX PHARMACEUTICALS INC    
Amendment Flag false    
Current Fiscal Year End Date --12-31    
Document Fiscal Period Focus FY    
Document Fiscal Year Focus 2021    
Document Type 10-K    
Document Annual Report true    
Document Period End Date Dec. 31, 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, $0.001 par value    
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    
Entity Shell Company false    
Entity Public Float     $ 161,163,094
Entity Common Stock, Shares Outstanding   146,949,320  
Auditor Name WithumSmith+Brown, PC    
Auditor Location San Francisco, California    
Auditor Firm ID 100    
ICFR Auditor Attestation Flag false    
OUM & CO. LLP [Member]      
Document Information [Line Items]      
Auditor Name OUM & CO. LLP    
Auditor Location San Francisco, California    
Auditor Firm ID 252