| Document and Entity Information | Aug. 12, 2021 |
| Cover [Abstract] | |
| Document Type | 8-K |
| Amendment Flag | false |
| Entity Registrant Name | Metacrine, Inc. |
| Document Period End Date | Aug. 12, 2021 |
| Entity Central Index Key | 0001634379 |
| Entity File Number | 001-39512 |
| Entity Incorporation State Country Code | DE |
| Entity Tax Identification Number | 47-2297384 |
| Entity Address, Address Line One | 3985 Sorrento Valley Blvd. |
| Entity Address, Address Line Two | Suite C |
| Entity Address, City or Town | San Diego |
| Entity Address, State or Province | CA |
| Entity Address, Postal Zip Code | 92121 |
| City Area Code | (858) |
| Local Phone Number | 369-7800 |
| Written Communications | false |
| Soliciting Material | false |
| Pre Commencement Tender Offer | false |
| Pre Commencement Issuer Tender Offer | false |
| Entity Emerging Growth Company | true |
| Entity Ex Transition Period | true |
| Security 12b Title | Common Stock, par value $0.0001 per share |
| Trading Symbol | MTCR |
| Security Exchange Name | NASDAQ |
