PrEP & PEP: HIV prevention before and after exposure
The two acronyms confuse everyone, so here's the whole distinction in one sentence: PrEP is the seatbelt you wear in advance; PEP is the airbag that deploys after the crash. Everything else is detail.
PEP: the 72-hour emergency option
Where to go: any emergency room, urgent care, or sexual health clinic. Walk in and say: "I may have been exposed to HIV and I need PEP." Those words start a well-rehearsed protocol — you will not be the first person that day to say them, and no one worth their license will judge you.
What it involves: a rapid HIV test first (PEP is for people who are currently negative), then a 28-day course of the same well-tolerated medications used to treat HIV. Modern regimens cause few side effects — some nausea or fatigue in the first days, usually fading. Finishing all 28 days matters; stopping early undermines the protection.
What it costs: in the US, insurance typically covers PEP, and manufacturer assistance programs or public health clinics cover most people who are uninsured — tell the provider about your situation and ask for the assistance paperwork. If the exposure was an assault, US programs generally cover PEP fully. In the UK and much of Europe, it's free through sexual health services and A&E.
Afterwards: you'll have follow-up HIV tests, typically at 4–6 weeks and again around 3 months. And if this is the second or third time you've needed PEP, that's not a personal failing — it's the textbook sign that PrEP would fit your life better.
PrEP: protection that's already there
PrEP means taking HIV-prevention medication on an ongoing basis, so that if an exposure happens, the virus can't establish itself. Taken as prescribed, it reduces the risk of getting HIV from sex by about 99%. There are now several ways to take it:
- A daily pill — the classic option, now available as an inexpensive generic. Protection builds within about 7 days for anal sex and about 21 days for vaginal sex.
- On-demand dosing ("2-1-1") — two pills 2–24 hours before sex, then one 24 hours later and one 48 hours later. Endorsed by WHO for anal sex when sex is predictable rather than constant.
- A shot every two months (injectable cabotegravir) — no pills to remember; given at a clinic.
- A twice-yearly injection (lenacapavir) — the newest option, approved in 2025, showing near-total protection in trials. Availability is still expanding, so ask whether your clinic offers it.
Who should consider it: anyone whose sex life includes partners of unknown HIV status, condomless sex outside mutual monogamy, a partner living with HIV who isn't yet undetectable, or a pattern of "I probably should have used a condom there." PrEP is standard preventive healthcare, not a confession about your lifestyle — clinicians prescribe it the way they prescribe travel vaccines. It works regardless of gender or hormones; see our guides for gay & bisexual men and trans sexual health for tailored specifics.
The routine: an HIV test before starting, then a check-in and test every 3 months (or aligned with injections). Kidney function is monitored for pill users — a simple blood draw.
The cost: generic daily PrEP is inexpensive almost everywhere; in the US, most insurance must cover PrEP and its follow-up visits without cost-sharing, and assistance programs fill the gaps. Free through the NHS in the UK.
What neither of them does
PrEP and PEP protect against HIV only. They do nothing for chlamydia, gonorrhea, syphilis, or pregnancy — condoms and regular testing still carry that load. The combination of PrEP plus routine testing is the modern gold standard for sexually active people with any HIV risk.
When to see a clinician
Immediately (today) if you may have been exposed within the last 72 hours. Soon and calmly if: you've needed PEP more than once, a partner has HIV and you're not on PrEP, or you simply want protection to be one less thing you think about. Bring questions — a good clinician would rather spend ten minutes on them than have you leave unsure.
Sources
- Centers for Disease Control and Prevention. HIV prevention: PrEP and PEP.
- World Health Organization. HIV — pre-exposure prophylaxis guidance.
- NHS. PrEP (pre-exposure prophylaxis).