PEP — emergency medication to prevent HIV after possible exposure

PEP — post-exposure prophylaxis — is a 28-day course of HIV medication taken after possible HIV exposure to prevent infection. When started quickly, PEP is highly effective. It is an emergency measure, not a regular prevention method. This page explains how PEP works, who it's for, where to get it, and what to expect.

1. What is PEP?

PEP stands for post-exposure prophylaxis. It's a combination of three antiretroviral medications, taken once or twice daily for 28 days, that can prevent HIV from establishing infection after possible exposure. The medications work by blocking the virus from replicating in your body during the critical period when infection would otherwise take hold.

2. What counts as HIV exposure — and what doesn't

PEP is appropriate after possible exposure to HIV. But not every situation counts as exposure — and understanding the difference can save you unnecessary worry. The final assessment is always made by a clinician, but this overview helps you decide whether to seek urgent care.

Possible HIV exposure

PEP may be appropriate after any of the following:

• Condomless anal or vaginal sex with someone known to have HIV (with detectable viral load) or whose status is unknown and risk factors are present
• A condom breaking during sex with someone with unknown or untreated HIV
• Sexual assault
• Sharing injection equipment with someone who has HIV or unknown status
• Needlestick injury (occupational exposure, mainly in healthcare workers)
• A blood splash to mucous membranes or broken skin

Usually NOT considered HIV exposure

When PEP is generally not needed

PEP is generally not needed if:

• The HIV-positive partner has a sustained undetectable viral load — Undetectable = Untransmittable (U=U)
• The exposure is considered very low or negligible risk
• More than 72 hours have passed since exposure (PEP is unlikely to work after this point)

3. The 72-hour rule

PEP must be started within 72 hours of exposure. After 72 hours, PEP is unlikely to be effective and is generally not prescribed.

But within that 72-hour window, sooner is dramatically better:

• Ideal: within 2 hours
• Strongly recommended: within 24 hours
• Maximum window: 72 hours

The reason: HIV begins replicating in immune cells within hours of exposure. The earlier PEP starts, the better it can block this replication before infection establishes in your body.

4. Where to get PEP

PEP is available at:

Sexual health clinics

In the Netherlands, the GGD (Gemeentelijke Gezondheidsdienst) Centre for Sexual Health provides PEP during office hours. Find your local GGD via soaaids.nl . In other European countries, sexual health or HIV clinics serve the same role.

Hospital emergency departments (outside office hours)

Most major hospitals can prescribe PEP via their emergency department. They will provide a starter pack and refer you to a sexual health clinic for follow-up. In the Netherlands, examples include OLVG in Amsterdam (020-5999111).

Sexual assault centres

If your exposure was through sexual violence, specialised sexual assault centres can provide PEP plus broader support. In the Netherlands, call 0800 0188 or visit centrumseksueelgeweld.nl (Centra Seksueel Geweld).

Outside the Netherlands

In the UK, PEP is free through NHS sexual health clinics and A&E departments. In other EU countries, PEP is generally available through sexual health clinics and hospital emergency rooms. Check with your local public health service.

5. How PEP works

A PEP course consists of three antiretroviral medications taken together, typically:

• Tenofovir disoproxil (NRTI)
• Emtricitabine (NRTI)
• A third agent — commonly dolutegravir or raltegravir (integrase inhibitor)

You take the medication daily for 28 days without missing doses. Adherence is critical — missed doses reduce PEP's effectiveness.

What PEP does

PEP works by blocking HIV from replicating in immune cells during the first weeks after exposure, when the virus would otherwise establish infection. When started quickly and taken consistently, PEP is highly effective.

What PEP doesn't do

• It does not protect against other sexually transmitted infections (gonorrhoea, chlamydia, syphilis, hepatitis)
• It is not 100% guaranteed — some PEP failures have been documented, usually associated with delayed start or missed doses
• It is not a substitute for ongoing prevention if you have continued risk of exposure

6. Side effects and what to expect

Modern PEP regimens are generally well-tolerated. Common side effects include:

• Nausea and stomach upset
• Headache
• Fatigue
• Diarrhoea

These typically improve within the first week. The clinician prescribing PEP will discuss what to expect and what to do if side effects are severe.

Important during the 28 days

• Take all doses on time
• Avoid stopping early even if you feel fine
• Use condoms and other prevention measures during the PEP course (you may still be able to transmit HIV during early infection if PEP fails)
• Avoid donating blood, sperm, or organs during PEP

If you cannot tolerate the medication, contact your clinic immediately — they may adjust the regimen rather than have you stop.

7. After PEP — follow-up testing

After completing the 28-day PEP course, follow-up testing is essential to confirm whether PEP successfully prevented infection. Standard schedule:

• HIV test at 4-6 weeks after completing PEP
• HIV test at 12 weeks after exposure (the standard window period mark)

If both tests are non-reactive, you can be confident PEP worked. Until then, continue using prevention measures.

PEP affects standard window period guidance because the antiretroviral medications can delay the development of detectable antibodies. Your clinician will advise on appropriate testing intervals — standard self-test guidance may need to be extended.

For more on the HIV window period and when self-tests become reliable, see our window period guidance .

8. PEP and PrEP — the difference

These two terms are often confused, but they refer to different prevention strategies:

If you find yourself needing PEP more than once, or if you have ongoing risk of HIV exposure, talk to a sexual health clinic about PrEP. PrEP is widely available across Europe — in the Netherlands through GGD sexual health clinics, in the UK through the NHS, and in most EU countries through national health services.

Frequently asked questions