Why PrEP Works

We know PrEP works. When taken as prescribed, it is proven to be up to 99% effective at preventing HIV. So, we wanted to outline four big clinical trials that prove PrEP is scientifically supported and generally awesome.

Study 1: iPrEX (men and transwomen who have sex with men)

In 2010, the iPrEX study was the first to prove that PrEP definitely works. It involved about 2,500 sexually active people from six countries that were at higher risk for HIV. The results showed that the efficacy of PrEP largely correlated with adherence, or how regularly the participants took the medication.

The participants who were randomly assigned PrEP were 44% less likely to contract HIV than those that were given the placebo. This percentage may not seem high, but it also included people with low adherence –  meaning not all participants took the medication as often as prescribed. When only looking at the people who did take it as prescribed, it decreased their risk by over 90%.

Study 2: Partners PrEP (heterosexual serodiscordant couples)

Another study, Partners PrEP, studied 4,500 heterosexual people in Kenya and Uganda. They were all in serodiscordant relationships, meaning they were in a relationship where one person was living with HIV and the other was HIV-negative. The people who were assigned PrEP and had detectable levels in their blood showed a 90% reduction in HIV risk than those that were given the placebo. Again, there was a strong correlation to adherence.

Study 3: Fem-PrEP (women)

Fem-PrEP was a study done on over 2000 women from Kenya, South Africa, and Tanzania. This study was actually stopped early because there were no signs of efficacy with PrEP. It’s important to talk about this study because the reason this study failed was because adherence was extremely low, meaning the subjects were not taking the drugs regularly.

Study 4: TDF-2 (heterosexual serodiscordant couples)

Similar to the Partners PrEP study, TDF-2 focused on individuals that were in a relationship where one person was living with HIV and the other was HIV-negative. The results showed 62% reduction in HIV, Again, adherence was a main factor to the lower rates.

In all four of these studies, the same conclusions were made about adherence and the efficacy of PrEP. When taken regularly, as prescribed, PrEP can reduce your risk of HIV by over 90%. More clinical trials are currently happening testing injectable and implanted PrEP to hopefully help with adherence. But until those methods are available, remember to take PrEP daily for maximum effectiveness!

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