Document and Entity Information - USD ($) $ in Millions	12 Months Ended
	Sep. 30, 2020	Dec. 15, 2020	Mar. 31, 2020
Document and Entity Information [Abstract]
Document Type	10-K
Entity Registrant Name	ESSA Pharma Inc.
Document Annual Report	true
Document Transition Report	false
Document Period End Date	Sep. 30, 2020
Entity File Number	001-37410
Entity Incorporation, State or Country Code	A1
Entity Address, Country	CA
Entity Tax Identification Number	47-2569713
Entity Address, Address Line One	Suite 720
Entity Address, Address Line Two	999 West Broadway
Entity Address, City or Town	Vancouver
Entity Address State Or Province	BC
Entity Address, Postal Zip Code	V5Z 1K5
City Area Code	778
Local Phone Number	331-0962
Title of 12(b) Security	Common Shares
Trading Symbol	EPIX
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	true
Entity Ex Transition Period	false
Entity Shell Company	false
Entity Central Index Key	0001633932
Current Fiscal Year End Date	--09-30
Document Fiscal Year Focus	2020
Document Fiscal Period Focus	FY
Amendment Flag	false
Entity Public Float			$ 83.3
Entity Common Stock, Shares Outstanding		33,600,122