PEP

Post-exposure prophylaxis. Emergency HIV medication that can stop the virus if taken within 72 hours of exposure.

PEP is emergency medicine that can stop HIV from infecting you, but only if you take it within 3 days (72 hours) of being exposed to the virus. The sooner the better.

Simplify

PEP stands for post-exposure prophylaxis. It's emergency medication that can stop from taking hold in your body after you've been exposed to the virus. It has to be started within 72 hours (3 days) of the potential exposure — and the sooner the better. It's not a morning-after pill for HIV in the casual sense, but it works on a similar principle: act fast after a risk event to prevent infection.

PEP is emergency HIV prevention medication taken after potential exposure.
It must be started within 72 hours — ideally as soon as possible. Every hour counts.
It's a 28-day course of antiretroviral drugs (the same type used to treat HIV).
It's available free from A&E departments and .
PEP is different from . PEP is taken after exposure. PrEP is taken before.

[DIAGRAM: Timeline diagram showing PEP — exposure event, 72-hour window to start, 28-day course, follow-up testing]

When you might need it

PEP is for situations where there's been a real risk of HIV transmission. That might include:

Unprotected anal or vaginal sex with someone who has HIV (or whose status you don't know)
A breaking during sex with someone who might have HIV
Sharing needles
Sexual assault

A healthcare professional will assess the level of risk before prescribing PEP. Not every exposure carries the same level of risk — for example, receptive carries a higher risk than . They'll ask you what happened so they can make the right call. This isn't about judging you — it's about working out whether PEP is appropriate.

How it works

PEP uses antiretroviral drugs — the same class of medication used to treat HIV. When taken quickly enough after exposure, these drugs can stop the virus from establishing itself in your body. Think of it as catching HIV before it gets a foothold.

The course lasts 28 days. You take tablets every day for the full month. It's important to complete the whole course, even if you feel fine — stopping early reduces the effectiveness.

PEP isn't 100% effective, but it's highly effective when started early. The sooner after exposure you begin, the better it works. After 72 hours, it's unlikely to help.

Where to get it

Time matters. If you think you need PEP, don't wait for a GP appointment — go to:

A&E (accident and emergency) — available 24/7. Tell the triage nurse you need PEP. They'll prioritise getting you seen quickly.
Sexual health clinics (GUM clinics) — during opening hours, this is usually the best option. Staff are experienced with PEP and will handle it efficiently.

PEP is free on the NHS. You don't need to pay for it, and you don't need a referral.

Side effects

PEP can cause side effects — nausea, tiredness, headaches, and diarrhoea are the most common. They're usually manageable and tend to improve as your body adjusts. The side effects are temporary; HIV is not. Completing the course matters more than comfort.

After PEP

Once you've finished the 28-day course, you'll need follow-up HIV tests — usually at 1 month and 3 months after finishing PEP — to confirm the treatment worked. [CHECK: current follow-up testing schedule] Until you get a confirmed negative result, use condoms.

If you find yourself needing PEP more than once, a clinic may talk to you about PrEP — the daily medication that prevents HIV before exposure. PrEP is more sustainable than repeated courses of PEP.

Things people get wrong

"PEP is a cure for HIV." It's not a cure — it's prevention. It stops HIV from establishing itself, but only if taken in time. If you already have HIV, PEP won't help (you'd need ART instead).

"You can take PEP whenever and it'll work." The 72-hour window is firm. After that, the virus has likely established itself and PEP won't be effective. Sooner is always better — ideally within 24 hours.

"Going to A&E for this is an overreaction." It's not. PEP is time-sensitive emergency medication. A&E is exactly where you should go if a clinic isn't open.

Things people ask about PEP

Will they judge me at A&E?

They shouldn't, and the vast majority of healthcare professionals won't. They deal with all kinds of situations. Your health is the priority, and they're trained to treat you with respect.

Is PEP the same as PrEP?

No. PEP is taken after a risk event (emergency). PrEP is taken before (ongoing prevention). Different timing, same goal — preventing HIV.

What if it's been more than 72 hours?

PEP is very unlikely to work after 72 hours. Go to a clinic anyway — they can advise on testing and monitoring, and assess whether there's any benefit to starting.

Can I get PEP after sexual assault?

Yes. If you've been sexually assaulted and there's a risk of HIV exposure, PEP should be offered as part of your care. You can access it through A&E or a sexual assault referral centre (SARC).

Where to get help

A&E — available 24/7 for emergency PEP access. Don't wait.
Sexual health clinics (GUM clinics) — PEP during opening hours, plus follow-up care.
Terrence Higgins Trust — information about PEP, PrEP, and HIV prevention.
NHS 111 — can direct you to the nearest service that provides PEP.

PEP stands for post-exposure prophylaxis. It's emergency medicine that can stop from taking hold in your body after you might have been exposed to the virus.

It has to be started within 72 hours (3 days) of the potential exposure. The sooner you start, the better it works. After 72 hours, it probably won't help.

You might need PEP if you had sex without a with someone who has HIV or whose status you don't know, if a condom broke, if you shared needles, or if you were sexually assaulted.

PEP is a course of tablets you take every day for 28 days. It's the same type of medicine used to treat HIV. You need to finish the full course for it to work properly.

You can get PEP for free from A&E (open 24 hours) or from a during their opening hours. You don't need an appointment. Going to A&E for this is not an overreaction — it's a time-sensitive emergency and that's exactly what A&E is for.

Some side effects like feeling sick or tired are common but usually manageable. They're temporary.

After finishing PEP, you'll need follow-up HIV tests to make sure it worked.

PEP is different from . PEP is taken after something risky has happened. PrEP is taken before, as ongoing protection.

HIV

Human immunodeficiency virus. Attacks the immune system. Can't be cured but with medication people live long, healthy lives.

HIV is a virus that attacks the body's ability to fight off illness. It can't be cured, but with daily medicine, people with HIV live long, healthy lives and can't pass it on.

PrEP

Pre-exposure prophylaxis. A daily medication taken by HIV-negative people at higher risk to prevent them getting HIV.

PrEP is a daily pill that people who don't have HIV can take to stop themselves from getting it. It's over 99% effective and free on the NHS.

Antiretroviral therapy

Daily medication used to manage HIV. Keeps the virus under control so people can live long, healthy lives.

Medicine taken every day to keep HIV under control. People who take it live long, healthy lives and can reach a point where they cannot pass the virus on.