How PrEP Actually Works to Prevent HIV

Take this medication consistently, and your risk of getting HIV goes way down

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Pre-exposure prophylaxis (PrEP) is a safe and effective medication to prevent HIV (human immunodeficiency virus) for those who are at a significant risk of contracting the infection. (Learn more about what PrEP is here.)

PrEP is kind of like a vaccine in that it prevents a virus from infecting the body despite being exposed to it, but it works a bit differently than a vaccine. Although a vaccine is often administered once and then can protect the body for several years, PrEP is a pill that must be taken every single day in order to properly protect against contracting HIV, according to hematologist Jeffrey Laurence, MD, of Weill Cornell Medicine in New York City.

PrEP consists of two medicines (tenofovir and emtricitabine) that work to stop HIV from multiplying inside the body after someone is exposed to it, say from sexual intercourse or sharing needles. Because the virus isn’t spreading, it cannot ever fully and permanently infect the body with HIV.

For PrEP to be effective, people at risk of HIV must take the oral PrEP pill every day and check in with their doctor every three months. Taking PrEP every day ensures that there is a steady presence of the medication in the bloodstream. (It’s similar to how birth control pills need to be taken every day so the proper hormone levels are always present to prevent pregnancy.)

PrEP is remarkably effective when taken consistently. It can reduce the risk of contracting HIV through sex by about 99 percent, and getting HIV through shared needles by at least 74 percent, according to the Centers for Disease Control and Prevention. However, doctors still recommend using a condom every single time you have sex for maximum protection against HIV and to protect against STDs.

If you think you may benefit from taking PrEP to prevent an HIV infection, learn more about the recommendations for who should take PrEP here.