Document And Entity Information - USD ($)	12 Months Ended
	Dec. 31, 2021	Mar. 14, 2022	Jun. 30, 2021
Document Information [Line Items]
Entity Central Index Key	0001053691
Entity Registrant Name	Diffusion 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	000-24477
Entity Incorporation, State or Country Code	DE
Entity Tax Identification Number	30-0645032
Entity Address, Address Line One	300 East Main Street, Suite 201
Entity Address, City or Town	Charlottesville
Entity Address, State or Province	VA
Entity Address, Postal Zip Code	22902
City Area Code	434
Local Phone Number	220-0718
Title of 12(b) Security	Common Stock, par value $0.001 per share
Trading Symbol	DFFN
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			$ 74,300,000
Entity Common Stock, Shares Outstanding		101,924,581
Auditor Name	KPMG LLP
Auditor Location	McLean, Virginia
Auditor Firm ID	185