PEP: emergency HIV prevention, within 72 hours

PEP stands for post-exposure prophylaxis — literally, "prevention after exposure." It's an emergency treatment: if you've had a possible exposure to HIV in the last three days, a short course of antiretroviral medicine can stop the virus from taking hold. Think of it as the morning-after option for HIV. It is safe, well-established, and recommended by the CDC and WHO — but it only works if you start in time.

01. What is PEP, and who is it for?

PEP is for HIV-negative people after a single, recent, higher-risk exposure. Common situations where a clinician will consider PEP include:

• Condomless sex, or a condom that broke or slipped, with a partner who has HIV or whose status you don't know.
• Sexual assault.
• Sharing needles or injection equipment.
• A needlestick or occupational exposure (for healthcare workers).

If you already take PrEP consistently, you're generally protected and don't need PEP. And if the exposure was more than 72 hours ago, PEP won't help — but you should still get tested and talk to a provider about starting PrEP going forward.

02. The 72-hour clock: why speed matters

This is the single most important thing to understand about PEP: it's a race against time. HIV needs a window to establish itself in the body, and PEP works by blocking that process. The earlier you start, the more effective it is.

03. How to get PEP right now

You have several fast routes. Pick whichever gets a first dose into you soonest.

04. What you'll actually take

PEP is a 28-day course of the same kinds of antiretroviral medicines used to treat and prevent HIV. A typical modern regimen is one or two tablets once a day, usually a combination such as tenofovir/emtricitabine (the same drugs in Truvada or Descovy) plus a third agent like dolutegravir or raltegravir.

The two rules that decide whether PEP works are simple: start fast, and take every dose for the full 28 days. Missing doses or stopping early is the main reason PEP fails. Set alarms, and if side effects bother you, call your provider rather than quitting — they can help.

05. How well does PEP work?

Started promptly and taken correctly, PEP is highly effective. In studies of occupational and sexual exposures, PEP reduced the risk of HIV by more than 80%, and the true benefit is likely higher when it's begun within 24 hours and taken without missed doses. No prevention method is 100%, which is exactly why timing and adherence matter so much.

“PEP is an emergency measure — every hour counts. Started quickly and completed fully, it can prevent HIV after an exposure.”— World Health Organization

06. PEP side effects

Modern PEP is much easier to tolerate than older regimens. Most people finish the 28 days with few problems. When side effects do happen, they're usually mild and fade as your body adjusts:

07. How much does PEP cost — and how to get it free

Without help, a 28-day PEP course can be expensive. But cost should never stop you — there are almost always ways to get it covered:

• Insurance typically covers PEP, often with a low or zero copay.
• Emergency rooms must provide emergency care regardless of ability to pay.
• Manufacturer assistance programs and government/PEPfar-style schemes provide free or reduced-cost PEP in many places.
• Sexual-health clinics frequently provide PEP free of charge.

When you call ahead, ask directly: "Do you have a PEP assistance program?" Staff deal with this every day.

08. After PEP: is it time for PrEP?

PEP handles one emergency. If you may be exposed to HIV again in the future, the better long-term answer is PrEP — pre-exposure prophylaxis — which you take before exposure and which is around 99% effective. Many people move straight from PEP to PrEP with no gap in protection; your provider can arrange this at your PEP follow-up.

Not sure which you need? Read PrEP vs PEP to see the difference at a glance, and if you're worried about sexually transmitted infections too, ask about Doxy-PEP.

09. Frequently asked questions

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