What is PEP? The 72-hour HIV emergency medicine, explained

PEP is a 28-day course of HIV medicine that can prevent infection after a possible exposure, if started within 72 hours. Who it's for and how to get it abroad.

If this might be you right now, stop reading and go to the urgent page. It tells you where to go first. Come back to this later.

Key points

PEP stands for post-exposure prophylaxis. It is HIV medicine you take after a possible exposure to stop the virus taking hold.
It must be started within 72 hours. Sooner is better: ideally within 24 hours.
You take it every day for 28 days.
It is for emergencies, not for regular use. If you’re often at risk, PrEP is the better tool.

How does PEP work?

After HIV enters the body, it takes a few days to establish a permanent infection. PEP is a combination of HIV medicines that stops the virus from multiplying during that window. If it works, the virus is cleared before an infection can take hold.

That is why timing matters so much. The US Centers for Disease Control and Prevention (CDC) puts it simply: PEP must be started within 72 hours, and “every hour counts.”

The deadline is shorter in some countries. Most guidelines, including those of the WHO, the US and the UK, use 72 hours. But some national guidance uses 48 hours: we found this in Italy, Norway and France when researching clinics there. Wherever you are, treat 72 hours as the outer limit and not as time you have. Go the same day.

Who is PEP for?

PEP is for people who don’t have HIV and may have just been exposed to it. The CDC lists these situations:

during sex, for example if a condom broke or wasn’t used
through sharing needles or other equipment to inject drugs
after sexual assault
at work, for example a needle-stick injury

A clinician decides whether PEP makes sense for you by asking what happened and when. They are not there to judge. If you’re unsure whether your situation counts, that is a reason to go and ask, not a reason to wait. Our guide to what counts as an HIV risk may help you think it through, but don’t let reading delay you.

One thing worth knowing: if the other person has HIV and is on effective treatment with an undetectable viral load, they can’t pass HIV on through sex. A clinician may tell you PEP isn’t needed in that case.

What happens when you go?

You say what happened and roughly when. A sentence is enough: “I may have been exposed to HIV about 20 hours ago and I’d like to be assessed for PEP.”
You have an HIV test. This checks that you didn’t already have HIV before this exposure. You may also be offered tests for other infections and for pregnancy.
If PEP is right for you, you start straight away. Some places give you a starter pack and ask you to come back for the rest.

What do the 28 days involve?

One set of pills a day, for 28 days. Take them at about the same time each day and finish the course.
Side effects are usually mild. The CDC says PEP is safe but may cause side effects like nausea in some people, and that these can be treated and aren’t life-threatening. Tell the clinic if they bother you rather than stopping.
Follow-up tests. US guidelines recommend a check-in about 24 hours after starting, then HIV tests at 4–6 weeks and again at 12 weeks after the exposure.
Use condoms in the meantime, until your follow-up tests are done.

PEP is very effective when started quickly and taken properly, but it is not a guarantee.

What if it’s been more than 72 hours?

PEP is unlikely to be offered, because it’s unlikely to work. It is still worth talking to a clinic: they can tell you when to test and answer your questions. See HIV test window periods.

Where can I get PEP abroad?

Almost everywhere, one of these will work:

A sexual health or HIV clinic, during opening hours. On our city pages, choose PEP now to see which clinics have PEP confirmed and which are open.
A hospital emergency department, at any hour. This is the usual route at night and at weekends.
A PEP hotline, where one exists. New York and New South Wales both run them; they’re listed on our city pages.

Cost varies a lot. In England, PEP is free from NHS sexual health clinics. Elsewhere you may pay for the consultation, the tests and the medicine. As an example, one Bangkok community clinic lists a PEP service from 2,900 THB. Travel insurance may or may not cover it. Ask about cost, but never let cost delay the first dose.

Go to the urgent page for the step-by-step.

PEP is not a plan

The CDC is clear that PEP is “for emergency situations only” and not a substitute for regular prevention. If you’ve needed PEP more than once, or think you might again, ask about PrEP at the same visit. Many clinics can move you from one to the other.

Sources

Checked 19 September 2026.

CDC, Preventing HIV with PEP
CDC, Antiretroviral postexposure prophylaxis after sexual, injection drug use, or other nonoccupational exposure to HIV: recommendations, 2025
NHS, HIV and AIDS: prevention
Terrence Higgins Trust, PEP

Quick answers

How soon do I need to start PEP?

As soon as possible, and no later than 72 hours (3 days) after the possible exposure. US guidelines say ideally within 24 hours. Every hour counts.

How long do you take PEP for?

Every day for 28 days. Finishing the full course matters, even if you feel fine.

Can I get PEP as a tourist?

Usually yes. Sexual health clinics and hospital emergency departments in most countries can start PEP. What you pay varies, from free in some public systems to the full cost of the medicine in others.

Is PEP the same as the morning-after pill?

No. The morning-after pill prevents pregnancy. PEP is HIV medicine. They are different medicines for different things, and you can need both.