PrEP (pre-exposure prophylaxis) is medicine that HIV-negative people take before possible exposure to prevent infection. It comes as a daily pill or an injection given by a clinician, and when taken as prescribed it lowers the risk of getting HIV from sex by about 99% CDC. It's for people who don't yet have the virus.
when taken as prescribed
when taken as prescribed
of daily dosing
of daily dosing
| Item | Value |
|---|---|
| HIV risk reduction (sex) | ~99% — when taken as prescribed |
| HIV risk reduction (injection use) | ≥74% — when taken as prescribed |
| Protection begins (anal sex) | ~7 days — of daily dosing |
| Protection begins (vaginal sex) | ~21 days — of daily dosing |
What PrEP is and how it works
PrEP is for people who don't have HIV but who could be exposed to it. The medicines keep a protective level of antiviral drug in your blood and the tissues where HIV would first try to take hold. If the virus shows up through sex or shared injection equipment, it can't establish a lasting infection because the drug blocks the steps it needs to copy itself. You're putting a defensive wall up ahead of time instead of scrambling after exposure.
This is what separates it from treatment. People living with HIV take medication to suppress the virus they already have; PrEP keeps HIV-negative people negative. It only works if there's enough drug on board, so the daily-pill versions need consistent dosing to reach full strength.
How effective is PrEP?
Taken as prescribed, PrEP reduces the risk of getting HIV from sex by about 99% and the risk from injection drug use by at least 74%. Those figures assume real-world adherence, and the gap between perfect and imperfect use is large. In trials, daily pills cut risk about 44% overall but roughly 92% among people who actually took them (iPrEx), on-demand 2-1-1 dosing reached 86% (IPERGAY), and the long-acting cabotegravir shot beat daily pills by 66% (HPTN 083). It only protects you if it's in your body. For a deeper breakdown, see how effective is PrEP.
Protection also takes time to build. Daily PrEP reaches maximum protection in about 7 days for receptive anal sex, and about 21 days for receptive vaginal sex and injection drug use. Until you hit those marks, keep using condoms. You're not fully covered on day one.
PrEP options: Truvada vs Descovy vs Apretude injection
There are three FDA-approved options. The right one depends on how you're at risk, your kidney and bone health, and whether daily pills fit your life.
| Option | What it is | How it's taken | Who it's for |
|---|---|---|---|
| Truvada | Daily pill (tenofovir disoproxil fumarate/emtricitabine) | One pill, every day | People at risk through sex or injection drug use |
| Descovy | Daily pill (tenofovir alafenamide/emtricitabine) | One pill, every day | People at risk through sex only — not for those at risk through receptive vaginal sex; gentler on kidneys and bones |
| Apretude | Injection (cabotegravir) | A clinician shot every 2 months, after two initial monthly shots | People at risk through sex who weigh at least 77 pounds (35 kg); removes daily-pill adherence as an issue |
Truvada is the broadest option and the only pill cleared for people who inject drugs. Descovy has a more favorable kidney and bone safety profile, which can matter if you have early kidney concerns, but it isn't approved for people assigned female at birth who are at risk through receptive vaginal sex, because the trial data didn't cover that route. Apretude is for anyone who'd rather not manage a daily pill; you trade pill-taking for a clinic visit every couple of months.
On the horizon, twice-yearly injectable lenacapavir produced zero infections among women in the PURPOSE 1 trial WHO, the strongest HIV-prevention result recorded so far. Availability is expanding, so ask your provider what's currently offered near you.
Who should take PrEP
PrEP is for HIV-negative adults and adolescents at substantial risk, and it's not just for gay men. The CDC bases eligibility on exposure rather than identity. You should consider it if any of these fit you:
- You have a sexual partner who is HIV-positive (including a partner whose viral load is suppressed but you want extra peace of mind).
- You don't consistently use condoms with partners whose HIV status you don't know.
- You've had a bacterial STI recently or have multiple partners.
- You inject drugs and share needles or other equipment.
HIV is far from rare in the US. About 38,800 people were newly diagnosed in 2023 CDC, 2023, with rates clustering in the South and in Washington DC. If you're unsure whether you qualify, the full criteria are laid out in who should take PrEP.
What PrEP does NOT protect against
PrEP is HIV-specific. It does nothing against other sexually transmitted infections like chlamydia, gonorrhea, syphilis, herpes, or HPV, and it doesn't prevent pregnancy. People on PrEP still benefit from condoms and routine STI screening; the quarterly visits are a natural moment to get tested. Skipping that screening is one of the most common mistakes I see, because PrEP can give a false sense that you're covered for everything.
How to get PrEP
Getting started is more accessible than people expect. Any primary care doctor, Planned Parenthood, sexual health clinic, or PrEP telehealth service (such as Nurx, Mistr, or FOLX) can prescribe it. You don't need a specialist.
The first visit confirms you're HIV-negative with a starting HIV test, checks your kidney function with a creatinine test, and screens for other STIs. You have to test negative for HIV before starting, because PrEP alone isn't enough to treat an existing infection and could encourage drug resistance. After you begin, you'll have check-ins every 3 months to reconfirm you're HIV-negative and monitor your health. With telehealth, much of this is done by mail-in kits and video visits.
Cost and how to get it free
Cost should rarely keep someone from PrEP. Truvada and Descovy are covered by most insurance plans with no cost-sharing, because the ACA requires preventive care to be free at the point of use. If you're uninsured, Gilead's Advancing Access program provides both medications at no cost to income-eligible patients; you can reach it at 1-800-226-2056 or gileadadvancingaccess.com. The AIDS Drug Assistance Program (ADAP) covers PrEP in every state for income-eligible patients.
The required labs can carry their own charge if you're uninsured; if that's a barrier, look into low-cost testing options so the bloodwork doesn't stop you from starting.
PrEP vs PEP: the key difference
These two get mixed up constantly, and the difference is timing. PrEP is taken on an ongoing basis before exposure to stay protected. PEP (post-exposure prophylaxis) is the emergency option taken after a single possible exposure; it must be started within 72 hours and taken for 28 days CDC. In the original occupational study, a prompt 28-day course cut HIV seroconversion by about 81%, which is why PEP is treated as a same-day emergency. They are not interchangeable: PEP is the fire extinguisher, PrEP is the smoke detector. If you've had a recent risk and the clock is still under 72 hours, don't wait on PrEP. Read PrEP vs PEP and get to care today.