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Post exposure prophylaxis

Post-exposure prophylaxis

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

What is PEP and can I use it instead of condoms?

Condoms are the best way of stopping HIV:

  • they can be free (from your doctor or sexual health clinic)
  • they are easy to find
  • there are no side effects
  • you only need to use one during sex
  • they don’t require medical help

However 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. 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. 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, have side effects and getting PEP is often not easy. Condoms on the other hand are cheap, available everywhere, have no side effects and only need to be used during sex (not for a month after sex like PEP).

Getting PEP

Post-exposure prophylaxis (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.

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 and only 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 that have side effects. 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, anal).
  • Whether the other person definitely had HIV, what was their ‘viral load’ (if this is known)?

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.

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.

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 the above number for help and advice.

Taking PEP

For Post-exposure prophylaxis (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 a dose is missed take the next dose as soon as you remember – don’t take double the dose.

Are there any side effects?

It is common for people taking PEP to get side effects. These will stop once the course of drugs has been completed - but for some people they can make sticking with PEP difficult. Headaches, tiredness, feeling sick and diarrhoea are common side effects.

If you are finding the treatment difficult, speak to the clinic that gave it to you; they can give you medication to help with side effects. Because of side effects some people need to take time off work or study while they are on PEP.

Is there anything I should avoid doing while taking PEP?

When taking PEP you will be advised not to have any further unprotected sex during the 28 days of treatment as this will make it more likely that PEP will not work.

As recreational drugs can have dangerous interactions with HIV medication, it’s advisable not to use them while taking PEP.

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

To be sure that no infection has taken place, three months after the course of PEP drugs has been completed you will be asked to have another HIV test. 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 24/8/2015 by TA

Date due for the next review: 24/8/2018

Content Author: R. Scholey

Current Owner: Health promotion

More information:

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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