PrEP is highly effective for preventing HIV.
- PrEP reduces the risk of getting HIV from sex by about 99% when taken as prescribed.
- Although there is less information about how effective PrEP pills are among people who inject drugs, we know that PrEP pills reduce the risk of getting HIV by at least 74% when taken as prescribed. Currently, PrEP shots are not recommended for people who inject drugs.
- PrEP is less effective when not taken as prescribed.
- For receptive anal sex (bottoming), PrEP pills reach maximum protection from HIV at about 7 days of daily use.
- For receptive vaginal sex and injection drug use, PrEP pills reach maximum protection at about 21 days of daily use.
- No data are available for PrEP pill effectiveness for insertive anal sex (topping) or insertive vaginal sex.
- We don’t know how long it takes for PrEP shots to reach maximum protection during sex.
Learn more about the PrEP effectiveness estimate.
Page last reviewed: June 6, 2022