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PEP (Post-Exposure Prophylaxis)


Post-exposure prophylaxis (PEP) is a treatment that can prevent HIV infection after the virus has entered a person's body.

PEP can stop HIV infection after the virus has entered the body:

  1. PEP is an emergency measure to be used as a last resort, eg if a condom breaks or you have a ‘slip up’ from your usual safer sex routine.
  2. PEP is a combination of powerful drugs and can be hard to get hold of, so it is no substitute for condoms, but it’s important to know about in case one day you or someone you’ve had sex with needs it.
  3. PEP is not guaranteed to always work but has a high success rate.
  4. It is free of charge but can only be prescribed by doctors and if certain criteria are met.

Sexual health and HIV clinics can provide it, as can Accident & Emergency departments of hospitals.

Regular family doctors (GPs) don’t give PEP.

  1. What is PEP?
  2. Getting PEP
  3. Taking PEP

What is PEP?

Post-exposure prophylaxis (PEP) is a month-long course of HIV drugs that someone takes very soon after sex which had a risk of HIV transmission. The drugs are the same ones taken by people with HIV.

How soon do I need to start PEP?

The sooner PEP is started, the more likely it is to work; within 24 hours is best, but no later than 72 hours (three days). After 72 hours PEP is unlikely to work.

How long do I need to take PEP for?

For PEP to work the drugs must be taken for four weeks. If someone stops taking it before 28 days it is unlikely that it will work.

If PEP is available, do I still need to use condoms?

Yes, condoms are the best way of stopping HIV.

PEP is not a ‘morning after’ pill to stop HIV (as it is not taken just once but must be taken every day for 28 days).

It is not a replacement for condoms. PEP drugs are powerful, may have side effects and getting PEP is often not easy.

Condoms on the other hand are cheap (or free from your doctor or sexual health clinic), widely available and only need to be used during sex (not for a month after sex like PEP).

Condoms also prevent other sexually transmitted infections (STIs) and unwanted pregnancy.

Getting PEP

PEP is available for free on the NHS but it is only given to people who meet national guidelines about its use. These guidelines help doctors decide who might be offered PEP and under which circumstances.

The UK PEP guidelines have recently been updated by the British Association of Sexual Health and HIV (BASHH) because the medicines used in PEP have changed.

Where can I get PEP?

The best place to go for PEP is a sexual health (GUM) clinic or an HIV clinic. These are usually only open during the week during office hours. If you need PEP over the weekend, outside of office hours or during a public holiday the best place to go is the Accident and Emergency (A&E) department of a hospital. A&E departments never close but there is no guarantee that an A&E doctor will agree to give someone PEP. PEP is not usually available from GPs (family doctors).

Find your nearest sexual health clinic.

What will happen if I ask for PEP?

PEP involves powerful and expensive drugs. To make sure it isn’t given to people with no real risk of infection, if you want PEP you will be asked questions about:

  • The person you had sex with (and the chances that person had HIV).
  • What kind of sex happened (vaginal, oral or anal?).
  • If the other person definitely had HIV, what was their ‘viral load’ (if this is known)? If the person you had sex with is living with HIV, but on treatment and has had an ‘undetectable viral load’ for at least six months, you will not need PEP.

Once a doctor has considered your risk, a decision will be made about whether PEP is appropriate. If so, you must first have an HIV test. This makes sure that you don’t already have HIV; if you do, taking PEP is not the treatment you need.

To help you work out if PEP is appropriate for you or someone you’ve had sex with you can call THT Direct on 0808 802 1221 or complete this online risk assessment.

However you need to start PEP as soon as possible within 24 hours, but no later than 72 hours (three days). If time is running out it's best to go straight to a sexual health or HIV clinic - or if it's outside of office hours, your nearest A&E.

What should I do if I find it difficult to get PEP?

Sometimes people face obstacles when asking for PEP. Medical staff or receptionists may not know about it or give out incorrect information such as ‘PEP is not available to the general public’.

If this happens, ask to speak to the ‘on-call HIV doctor’ who will know all about PEP. If you have nearby options, you could go to another hospital. You can call THT Direct on 0808 802 1221 for help and advice.

Taking PEP

Which drugs are used in PEP and do they have side effects?

The medication now used for PEP is a tablet called Truvada (which contains tenofovir and emtricitabine) and two tablets of raltegravir (Isentress). These are antiretroviral drugs commonly used to treat HIV.

PEP used to normally consist of Truvada and a drug called Kaletra (which contains lopinavir and ritonavir), but the Kaletra has been swapped for raltegravir.

This is because it has fewer side effects and is better tolerated.

If you do get side effects from PEP they are likely to be mild ones in the first few days, such as nausea, headaches or tiredness.

How to take PEP:

For PEP to have the best chance of working it must be taken exactly as instructed by a doctor and for 28 days. Skipping doses, or not taking the pills for the full month, makes it likely that PEP will not work - if you miss more than 48 hours of PEP it will be discontinued.

If you forget to take your PEP and remember in less than 24 hours, take the next dose as soon as you remember. If more than 24 hours have passed, take the next dose you are due to take - don't take double the dose.

Is there anything I should avoid doing while taking PEP?

As recreational drugs can have dangerous interactions with HIV medication, it’s advisable not to use them while taking PEP. Tell the doctor assessing you about any recreational drugs, herbal treatments or over-the-counter medicines you're taking.

What should I do after my course of PEP has finished?

To be sure that no infection has taken place, you will be tested for HIV (along with hepatitis and syphilis) 8 to 12 weeks after finishing the course of PEP. If you decide not to take PEP an HIV test is recommended anyway, along with a check up for sexually transmitted infections.

PrEP - pre-exposure prophylaxis ››

‹‹ Back to: HIV treatment



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The Information Standard: Certified member

This article was last reviewed on 7/4/2016 by Anna Peters

Date due for the next review: 7/4/2019

Content Author: R. Scholey

Current Owner: Health promotion

More information:

UK Guideline for the use of HIV Post-Exposure Prophylaxis Following Sexual Exposure (PEPSE), Martin Fisher, Eleanor Briggs, Fiona Cresswell, Julie Fox, Justin Harbottle, David Hawkins, Martin Murchie, Keith Radcliffe, Paul Rafferty, Alison Rodger, Laura Waters. British Association for Sexual Health and HIV, 2015

Do condoms work?, by Gus Cairns, NAM, Aidsmap

Can post-exposure prophylaxis (PEP) stop me getting HIV?, NHS Choices, September 2015

Gay men Fighting AIDS by Carl Burnell, PEP, December 2014

Condoms, NHS Choices, January 2015

Factsheet: emergency HIV treatment (PEP), Avert, March 2016

Change to recommended regimen for post-exposure prophylaxis (PEP), Expert Advisory Group on AIDS, September 2014

HIV treatment booster drugs are most likely to have dangerous interactions with methamphetamine, mephedrone, MDMA and ketamine, by Roger Pebody, NAM, Aidsmap, August 2015

HIV drug interactions - Antiretrovirals and recreational drugs, University of Liverpool, May 2015

Interactions with recreational drugs, NAM, Aidsmap

Post-exposure prophylaxis (PEP) NAM. 2011

Benn P, Fisher M et al., UK guideline for the use of post-exposure prophylaxis for HIV following sexual exposure (2011), International Journal of STD & AIDS. Volume 22. December 2011.

Department of Health. EAGA guidance on HIV post-exposure prophylaxis. 2015

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