PrEP Effectiveness

PrEP Effectiveness
How effective is PrEP?

Learn about your HIV risk and how to lower it.

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 is among people who inject drugs, we do know that PrEP reduces the risk of getting HIV by at least 74% when taken as prescribed.
  • PrEP is much less effective when it is not taken as prescribed.

How long do I have to take PrEP before it is highly effective?

PrEP pill
  • PrEP reaches maximum protection from HIV for receptive anal sex (bottoming) at about 7 days of daily use.
  • For receptive vaginal sex and injection drug use, PrEP reaches maximum protection at about 21 days of daily use.
  • No data are available for insertive anal sex (topping) or insertive vaginal sex.

Learn more about the PrEP effectiveness estimate.