Being on PrEP means you’re taking medication to prevent HIV before you’re exposed to the virus. PrEP stands for pre-exposure prophylaxis, and it works by keeping enough of the drug in your body so that if HIV enters through sex or injection drug use, the virus can’t take hold and establish a permanent infection. It’s available as a daily pill or as an injection given by a healthcare provider, and when taken consistently, it’s one of the most effective tools available for HIV prevention.
How PrEP Works in Your Body
PrEP medications block a critical step in HIV’s life cycle. HIV normally needs to hijack your cells to copy itself and spread. The drugs in PrEP interfere with that copying process, so even if the virus enters your body during sex or through a shared needle, it can’t replicate and establish an infection. The key is that the medication needs to already be present in your tissues at sufficient levels when exposure happens. That’s why consistency matters: the drug has to be there waiting, not taken after the fact.
Pills vs. Injections
There are currently four FDA-approved PrEP options, split between daily pills and long-acting injections.
Daily Pills
Two oral medications are approved for daily use. Both combine two anti-HIV drugs in a single pill. Truvada (and its generic versions) is approved for anyone at risk of HIV through sex or injection drug use. Descovy is approved for men and transgender women at risk through sex, but it has not been studied for protection during receptive vaginal sex, so it’s not recommended for that purpose.
Injectable Options
If you’d rather skip the daily pill, two injectable forms exist. Apretude is given by a healthcare provider every other month. Lenacapavir (Yeztugo) requires only two injections per year, making it the least frequent dosing schedule available. With lenacapavir, you take oral pills for the first two days to quickly build up protective drug levels before switching to the injection schedule. Both injectables are approved for adults and adolescents who weigh at least 77 pounds.
How Long Until You’re Protected
PrEP pills don’t work instantly. The timeline to maximum protection depends on the type of exposure you’re trying to prevent. For receptive anal sex, daily pills reach full protective levels in about 7 days. For receptive vaginal sex and injection drug use, it takes longer: approximately 21 days of daily use to reach maximum protection. During that ramp-up period, you should use additional protection like condoms.
What Taking PrEP Looks Like Day to Day
If you’re on daily oral PrEP, the routine is straightforward: one pill at roughly the same time each day. Most people build it into an existing habit, like brushing their teeth or eating breakfast. Missing occasional doses reduces the drug’s effectiveness, so consistency is important. Many people set a phone alarm or use a pill organizer.
If you’re on an injectable, the day-to-day burden is much lower. You visit your provider for an injection on schedule and don’t think about it between appointments. The trade-off is that you need to keep those appointments reliably, since protection drops if you fall behind.
Regardless of which form you use, being on PrEP also means regular check-ins with your healthcare provider. These visits typically happen every few months and include HIV testing to confirm you’re still negative, since PrEP is strictly a prevention tool and should not be taken by someone who already has HIV. Your provider will also monitor kidney function and screen for other sexually transmitted infections.
Side Effects
Most people tolerate PrEP well. The most commonly reported side effects with the oral pills are nausea, headache, and stomach discomfort, and these tend to fade within the first few weeks as your body adjusts. Serious side effects are uncommon but can include changes in kidney function, which is why regular lab work is part of the routine.
One concern that sometimes comes up is bone density. Research from a large PrEP demonstration project found that people taking daily oral PrEP experienced a modest decline in spine bone density of about 1.2% and a 0.5% decrease at the hip. These are small changes, and the decline appeared to level off after the first 24 weeks rather than continuing to worsen over time. For most healthy adults, this is not clinically significant, but it may be worth discussing with your provider if you have existing bone health concerns. The newer pill formulation (Descovy) and the injectable options were developed in part to reduce these kidney and bone effects.
Who PrEP Is For
PrEP is designed for people who are HIV-negative but have an ongoing risk of exposure. That includes people who have a sexual partner living with HIV, people who don’t consistently use condoms with partners whose HIV status is unknown, people who have had a sexually transmitted infection in the past six months, and people who share needles or injection equipment. It’s not limited to any gender, sexual orientation, or age group.
Before starting, you’ll need an HIV test to confirm you’re negative, along with kidney function tests and screening for hepatitis B. Your provider uses these results to determine which PrEP option is safest and most appropriate for you.
What PrEP Doesn’t Do
PrEP is highly effective at preventing HIV, but it does not protect against other sexually transmitted infections like gonorrhea, chlamydia, or syphilis. It also doesn’t work as a treatment for HIV. If someone who already has HIV takes PrEP instead of proper treatment, the virus can develop resistance to the medications, making future treatment harder. That’s the main reason regular HIV testing is built into the process of being on PrEP.
Getting Access
PrEP is available through primary care providers, sexual health clinics, and many community health centers. Generic versions of Truvada are available, which has significantly reduced the cost of the oral pill option. Many insurance plans cover PrEP with no out-of-pocket cost, and manufacturer assistance programs and federal programs like the Ready, Set, PrEP program exist for people without insurance. Your provider’s office or a local HIV prevention organization can help you navigate coverage options specific to your situation.