What is PrEP? PrEP, or pre-exposure prophylaxis, is a medication taken to prevent HIV infection. It is designed for people who do not have HIV but are at high risk of contracting it through sex or injection drug use. When taken as prescribed, PrEP is highly effective, reducing the risk of getting HIV from sex by about 99% and from injection drug use by at least 74% PrEP safety and interactions PrEP is safe to take. Some people experience side effects like diarrhea, nausea, headache, fatigue, and stomach pain. These side effects usually go away over time. However, you should talk to your health care provider about any side effects that are severe or do not go away. PrEP and birth control There are no known interactions between PrEP and hormone-based birth control methods, e.g., the pill, patch, ring, shot, implant, or IUD. It is safe to use both at the same time. PrEP and hormone therapy There are no known drug conflicts between PrEP and hormone therapy. It is safe to use both at the same time. PrEP effectiveness PrEP greatly reduces your chance of getting HIV from sex or injection drug use. 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. Deciding if PrEP is right for you PrEP can help protect you if you don’t have HIV and any of the following apply to you: You have had anal or vaginal sex in the past 6 months and you have a sexual partner with HIV (especially if the partner has an unknown or detectable viral load), have not consistently used a condom, or have been diagnosed with a sexually transmitted disease in the past 6 months. You inject drugs and you have an injection partner with HIV, or share needles, syringes, or other drug injection equipment (for example, cookers). You have been prescribed PEP (post-exposure prophylaxis) and you report continued risk behavior, or have used multiple courses of PEP. You may choose to take PrEP, even if the behaviors listed above don’t apply to you.