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Post-exposure prophylaxis (PEP) after sexual assault

What is PEP?

Post-exposure prophylaxis (PEP) are medicines that try to remove any HIV virus before it has a chance to infect you. HIV is an infection that can damage your immune system and put you at risk of serious illness.

If taken properly, PEP will prevent the infection from starting in around 95 percent of cases.

It is not a cure for HIV, so if you have already been infected with HIV, PEP will not stop it. There are other medicines that can control HIV, but not cure it.

Have I definitely been in contact with the HIV virus?

We do not know if you have definitely been in contact with someone with HUV virus. We will work out what your risk is after carefully considering what has happened to you. We will then advise you if there are strong reasons to take PEP.

Do I need PEP?

Contact with blood, saliva or semen may put you at risk. The risk depends on what has happened to you, who has hurt you and what we found when we examined you.

Do I have to take PEP?

It is your decision to take PEP or not. A discussion with your doctor should help you make this decision.

However, once you have decided to take it, you need to take the medicines every 12 hours, for 28 days. If you do not take them for this long then they will not work. 

When should I start PEP?

Ideally, it should be started as soon as possible. It is most effective if started within 12 hours but can be started anytime within 3 days of a sexual assault 

Are there any side effects?

Usually, PEP is very well tolerated. Sometimes people experience:

  • feeling sick and vomiting
  • diarrhoea
  • headache
  • trouble sleeping
  • stomach ache

These side effects are usually do not happen for very long. You can be given medication to make some of these side effects less of a problem.


If you get a rash or flu-like illness either during the time you take PEP or soon after, you need to stop the PEP and seek immediate medical attention

There are also very rare but life-threatening side effects such as:

  • liver failure
  • kidney failure

You will have blood and urine tests to check for these.

Does PEP interfere with other medicines?

Yes, PEP can interfere with other medicines. Please tell your doctor if you are taking any other medication, including medicines you have bought over the counter from the chemist, vitamins and herbal remedies.

PEP has an unpredictable impact on illegal and legal highs which can be dangerous. Do not use recreational drugs whilst taking PEP.

Can I still have sex when on PEP?

If you are having sex, you need to use condoms for at least 4 months to prevent HIV from spreading to your partner. It is important to discuss the reasons for this with your partner.

With the most commonly prescribed PEP, this will not affect the contraceptive pill or implant. If an alternative PEP medication is required, your doctor will discuss this with you.

You should also take care not to share razors or toothbrushes with other people until you have been given the all-clear.

If you think you may have been in contact with HIV again, please seek advice.

How do I know if I have HIV?

Your doctor will do a blood test before you start PEP and again 4 months later.

Are there any other infections I need to be protected from?

We will also offer you the Hepatitis B immunisation which will protect you from the Hepatitis B virus. We will offer you testing for other sexually transmitted infections such as gonorrhoea and chlamydia.

What if I could be pregnant?

If you think you could be pregnant, please tell your doctor. Your doctor will perform a pregnancy test at the centre regardless. Even in early pregnancy PEP is usually recommended. Your doctor will discuss the benefits and risks of PEP with you.

How do I get PEP?

Your doctor will give you a starter pack before you leave the hospital. You need to come back in 3 to 5 days to get more and to check about side effects.

What do I do if I forget to take PEP?

If you have forgotten to take your dose within 24 hours, you should take the missed dose immediately. Then take your next dose at the normal time.

If you have forgotten your dose for 24 to 48 hours, do not take the doses you have missed. Wait until your next dose would have been due and then start to take your PEP again as normal.

If it has been over 48 hours, stop taking PEP and tell your medical professional.

How do I take PEP?

You should take one of each tablet as soon as you are given them.

  • Truvada is blue (taken once a day)
  • Raltegravir is pink (is taken twice a day 12 hours apart)

What do I do if I have any problems with the PEP?

Your doctor can answer any questions you have before you leave the department, or when you come back in 3 to 5 days time.

Contact us

Please call the Safeguarding Support Unit on 0114 226 7803 between 9am and 5pm Monday to Friday if you have any problems with your medication. If you have an urgent concern outside those hours please contact your local GP or A&E.

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Please note: this is a generic information sheet relating to care at Sheffield Children’s NHS FT. These details may not reflect treatment at other hospitals. This information is not intended as a substitute for professional medical care. Always follow your healthcare professionals’ instructions. If this resource relates to medicines, please read it alongside the medicine manufacturer’s patient information leaflet. If this information has been translated into another language from English, efforts have been made to maintain accuracy, but there may still be some translation errors. If you are unsure about any of the guidance in this resource or have specific questions about how it relates to your child, always ask your healthcare professional for further advice.

Resource number: SFG2

Resource Type: Article

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Safeguarding Support Unit

Sheffield Children’s Foundation NHS Trust

Western Bank

S10 2TH


Western Bank
S10 2TH

United Kingdom

Switchboard: 0114 271 7000

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