What is PEP?

PEP stands for Post Exposure Prophylaxis.

This is when someone takes a short course of HIV drugs (called ART) after a significant sexual risk. ART involves taking a combination of three HIV meds every day for four weeks.

The word PEPSE  is sometimes used – it stands for PEP after Sexual Exposure.

How soon do you need to take PEP?

PEP needs to be taken as soon after exposure as possible.

This is preferably within hours rather than days. Most guidelines have a cut off for PEP of 48 hours after exposure.

Even though in the UK you can get PEP for up to 72 hours it is less likely to work when it is used this late.  The longer the delay the less the chance that PEP will work.

Before getting PEP you will need to talk about your risk. This involves talking about the type of sex and whether you know the HIV status of your partner.

HIV testing before PEP

You need to have a rapid HIV test before starting PEP.

These tests give the result within 30 minutes. This test only tells you whether you were HIV positive three months ago. It tells you nothing about the recent risk.

The HIV test is essential. If you are HIV positive without knowing it, a short course of treatment could cause drug resistance.

Where to get PEP

You can get PEP at any accident and emergency (A&E) department. This means it is available 24 hours a day. You can also access PEP from a sexual health clinic during working hours.

Testing for HIV after PEP

You need to wait 28 days after the last dose of PEP before testing for HIV. This is because PEP can sometimes  just delay infection.

During the time on PEP, the meds might be keeping your viral load undetectable.

However, even though HIV is difficult to catch, it is safer to use condoms

Until you know for certain whether or not you are HIV positive, it is better to assume that you might be HIV positive. This means using condoms with partner’s who might be HIV negative.

Changing from PEP to PrEP

Some people start PrEP after the course of PEP finishes.

PrEP uses two HIV meds, taken either daily or before and after sex, to also prevent infection.

Changing to PrEP is sometimes an option when there is still a high risk of HIV.

Moving straight to PrEP has a small risk of not knowing whether or not the PEP was effective.

U=U: when PEP is not needed

If your partner was HIV positive and taking HIV treatment the risk to you may already be zero. It this case you don’t need PEP.

If an HIV positive has an undetectable viral load on treatment there is no risk of sexual transmission. This is also called U=U for undetectable = untransmissable. See U=U and below.

Can I use my partner’s meds as PEP?

Using someone else’s meds is not recommended. Some HIV drugs should never be used as PEP.

However, some HIV drugs have been studied for preventing HIV. These are tenofovir DF and FTC (in one pill called Truvada) and tenofovir alafenamide and FTC (in a single pill called Descovy). A single dose of either of these medicines would provide more rapid cover while you get to a clinic and wait to be seen.

TDF/FTC is now widely used to reduce the chance of HIV transmission when taken by HIV negative people. These studies also showed these drugs to be safe.

This would only be recommended as a single dose while you are waiting to get to HIV clinic for PEP.

However, if the HIV positive person is already on treatment and has an undetectable viral load, they will not be infectious. In these circumstances, guidelines say that the risk is so low as to not recommend PEP.

In the UK, HIV meds that must NOT be used as PEP include:

  • Any type of NNRTI (nevirapine, efavirenz, etravirine or rilpivirine).
  • Atripla or Eviplera (which both contain an NNRTI)
  • Abacavir (or Kivexa or Trizivir that contain abacavir).

This is because these drugs have a low risk very serious side effects, including hypersensitivity reactions and severe skin rash. With some NNRTIs the risk can be higher for someone with a stronger immune system that when they are used for treatment in someone who is HIV positive.

Some countries include efavirienz as part of PEP.

Last updated: 1 June 2021.