I'm considering using pre-exposure prophylaxis (PrEP) to prevent an HIV infection. How effective is PrEP?

Answer From Stacey A. Rizza, M.D.

Pre-exposure prophylaxis (PrEP) can help prevent HIV infection in people who don't have HIV and are at risk of becoming infected. PrEP involves taking the combination drug emtricitabine-tenofovir (Truvada) or emtricitabine plus tenofovir alafenamide (Descovy) every day. Having PrEP medicine in your bloodstream can stop HIV from taking hold and spreading in your body.

A person who takes Truvada every day can lower his or her risk of getting HIV from sex by more than 99% percent and from injection drug use by more than 74% percent, according to the U.S. Centers for Disease Control and Prevention. Research suggests that Descovy is similarly effective in reducing the risk of getting HIV from sex. However, Descovy hasn't been studied in people who have receptive vaginal sex.

Research suggests that PrEP is less effective when it isn't taken daily. This may be because there isn't enough medicine in your body to block HIV from taking hold and spreading. Along with PrEP use, taking steps such as using condoms can further reduce your risk of HIV infection. PrEP doesn't prevent other sexually transmitted infections, so you'll still need to practice safe sex.

You'll also need an HIV test before you start taking PrEP and then every three months as long as you're taking it.

If you're considering PrEP, talk to your doctor about whether it's the right HIV prevention strategy for you.


Stacey A. Rizza, M.D.

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May 14, 2021 See more Expert Answers