What is PEP?
PEP (Post-Exposure Prophylaxis) is a short course of antiretroviral medicines taken after a possible exposure to HIV to prevent infection. It must be started as soon as possible — and no later than 72 hours (3 days) after the exposure. The sooner it is started, the more effective it is. PEP is not a morning-after pill for HIV; it is a 28-day treatment course that works by stopping the virus from replicating before it can establish a permanent infection.
Who should take PEP?
PEP is recommended when you have had a recent exposure that carries a meaningful risk of HIV transmission. This includes: unprotected anal or vaginal sex with someone who is HIV positive or whose status is unknown; sharing needles or other drug-injecting equipment; and sexual assault. PEP is not appropriate for people who are already HIV positive, or for routine low-risk situations — it is an emergency medication for genuinely high-risk exposures.
Where can you get PEP in the UK?
In the UK, PEP is available free of charge on the NHS. Outside of sexual health clinic opening hours, you can access it from any A&E department — 24 hours a day, 7 days a week. Sexual health clinics are often the better choice if they are open, as staff are very familiar with the process. Some pharmacies also carry PEP under patient group directions. Do not wait until the clinic opens if it means missing the 72-hour window — go to A&E immediately.
What are the side effects of PEP?
PEP commonly causes nausea, diarrhoea, headaches, and fatigue — especially in the first week. Most people find these manageable, and symptoms usually ease after 7–10 days. Taking tablets with food can help reduce nausea. It is important to complete the full 28-day course even if you feel side effects, as stopping early reduces effectiveness. Contact your prescribing clinic if side effects are severe.
Does PEP definitely work?
PEP significantly reduces the risk of HIV infection when taken correctly and started promptly, but it is not 100% effective. Its effectiveness depends on how soon it is started, whether you complete the full course, and the level of exposure. After completing PEP, you should have an HIV test at 45 days and again at 90 days to confirm the result. During and after the course, continue using condoms to avoid re-exposure and to protect partners.