| Document and Entity Information | May 05, 2021 |
| Cover [Abstract] | |
| Entity Registrant Name | Acadia Pharmaceuticals Inc. |
| Amendment Flag | false |
| Entity Central Index Key | 0001070494 |
| Document Type | 8-K |
| Document Period End Date | May 5, 2021 |
| Entity Emerging Growth Company | false |
| Entity Incorporation, State or Country Code | DE |
| Entity File Number | 000-50768 |
| Entity Tax Identification Number | 06-1376651 |
| Entity Address, Address Line One | 12830 El Camino Real |
| Entity Address, Address Line Two | Suite 400 |
| Entity Address, City or Town | San Diego |
| Entity Address, State or Province | CA |
| Entity Address, Postal Zip Code | 92130 |
| City Area Code | 858 |
| Local Phone Number | 558-2871 |
| Written Communications | false |
| Soliciting Material | false |
| Pre Commencement Tender Offer | false |
| Pre Commencement Issuer Tender Offer | false |
| Security 12b Title | Common Stock, par value $0.0001 per share |
| Trading Symbol | ACAD |
| Security Exchange Name | NASDAQ |
