| Document and Entity Information | Oct. 26, 2020 |
| Cover [Abstract] | |
| Document Type | 8-K |
| Amendment Flag | false |
| Document Period End Date | Oct. 26, 2020 |
| Entity Registrant Name | ESSA Pharma Inc. |
| Entity Central Index Key | 0001633932 |
| Entity Emerging Growth Company | true |
| Entity Ex Transition Period | false |
| Entity Incorporation, State or Country Code | A1 |
| Entity File Number | 001-37410 |
| 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, Country | CA |
| Entity Address, Postal Zip Code | V5Z 1K5 |
| City Area Code | 778 |
| Local Phone Number | 331-0962 |
| Written Communications | false |
| Soliciting Material | false |
| Pre-commencement Tender Offer | false |
| Pre-commencement Issuer Tender Offer | false |
| Title of 12(b) Security | Common Shares, no par value |
| Trading Symbol | EPIX |
| Security Exchange Name | NASDAQ |
