| Cover | Sep. 22, 2021 |
| Cover [Abstract] | |
| Document Type | 8-K |
| Amendment Flag | false |
| Document Period End Date | Sep. 22, 2021 |
| Entity File Number | 001-35776 |
| Entity Registrant Name | ACASTI PHARMA INC. |
| Entity Central Index Key | 0001444192 |
| Entity Tax Identification Number | 98-1359336 |
| Entity Incorporation, State or Country Code | A8 |
| Entity Address, Address Line One | 3009, boul. de la Concorde East |
| Entity Address, Address Line Two | Suite 102 |
| Entity Address, City or Town | Laval |
| Entity Address, State or Province | QC |
| Entity Address, Postal Zip Code | H7E 2B5 |
| City Area Code | 450 |
| Local Phone Number | 686-4555 |
| 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 per share |
| Trading Symbol | ACST |
| Security Exchange Name | NASDAQ |
| Entity Emerging Growth Company | false |
