HIV PEP (Post Exposure Prophylaxis)

HIV PEP (Post Exposure Prophylaxis)

A treatment that can stop HIV infection after the virus has entered a person's body

What is PEP?

PEP stands for Post Exposure Prophylaxis. It is a combination of medicines that can be taken after possible exposure to HIV to prevent someone getting the infection themselves.

PEP is available from sexual health clinics and hospital emergency departments (EDs). It should be given as soon as possible after potential exposure to HIV (ideally within 24 hours) but can be given up to 72 hours afterwards.

PEP treatment is a combination of medicines (Tenofovir Disoproxil 245mg/Emtricitabine 200mg plus Raltegravir 1200mg) taken once daily for 28 days. It is only given in circumstances where there is a high risk of HIV transmission, and it only protects against HIV, not other sexually transmitted infections (STIs).

How to get PEP

If you think you have been exposed to HIV and would like to discuss PEP, we advise accessing care as soon as possible. Please call us on 01273 523 388.

Phone line opening times:

Monday 9.15am to 4.30pm
Tuesday 9.15am to 4.30pm
Wednesday 12.30pm to 4.30pm
Thursday 9.15am to 4.30pm
Friday 9.15am to 4.30pm

If you need PEP over the weekend, on a bank holiday or outside of office hours, the best place to go is an ED and ask to start HIV PEP.

Who is eligible for PEP?

PEP and follow up testing are available for free from NHS services. You do not need to have a Brighton and Hove (B&H) address or to be already registered as a patient with us to attend our clinics for PEP. Similarly, if you need PEP when you are away from B&H, don’t delay accessing services until you return, you can attend any sexual health clinic or Emergency Department (A&E) nationwide to access PEP.

PEP assessment following potential sexual exposure (PEPSE)

PEP is not suitable in every circumstance, so the clinician seeing you will need to ask some questions about the type of sex you have had and the person you have had sex with to assess the level of risk. PEP is not needed if the sex was with someone living with HIV who is on effective treatment, meaning they have an undetectable level of virus in their bloodstream. If you do not have any information about the person you had sex with, a clinician will take as many details as possible to help decide if you need PEP. If you are attending following a sexual assault, we can offer other support and advice alongside a PEP assessment.

PEP is often given following:

  • Unprotected receptive anal sex with someone of unknown HIV status.
  • Unprotected receptive anal sex with someone who has HIV and is not yet on treatment, or who isn’t on effective HIV treatment (if you are unsure the clinician seeing you will be able to discuss this).
  • Unprotected receptive vaginal sex with someone who has HIV and isn’t on treatment, or who’s level of virus in the blood isn’t yet undetectable (if you are unsure the clinician seeing you will be able to discuss this).

PEP is sometimes given following:

  • Unprotected insertive vaginal sex with someone known to be HIV-positive with an unknown or detectable level of HIV in the blood.
  • Unprotected insertive anal sex with someone known to be HIV-positive with an unknown or detectable level of HIV in the blood.

In other circumstances, including oral sex, PEP is usually not recommended, although it can be discussed with a clinician if you have any concerns.

What will happen when I attend the clinic for PEP?

On the day:

When you attend a clinic asking for PEP we will try to see you as soon as possible to make an assessment. If you are very close to the 72 hour deadline, please let reception staff know so they can alert a member of staff to this.

The clinician will ask a series of questions to assess the risk of HIV exposure. These will include the type of sex you had, any information you have about the person you had sex with, whether you consented to this sex, whether any condom was used. They will also need to know if you have any diagnosed medical conditions, if you take any medications and if you have any allergies. If you are at risk of pregnancy they will ask about any contraception you use and when your last period was. You may also be offered emergency contraception.

It is really important that you let us know if you take any medications, including those bought over the counter or taken recreationally as some drugs can affect the ability of PEP to prevent HIV infection.

Before starting PEP, we will need to do some testing. These will include a rapid point of care HIV test (to check that you do not already have HIV), some blood tests (to check for STIs, immunity to hepatitis A and hepatitis B, and to assess your kidney and liver function) and swab tests (for chlamydia and gonorrhoea).

If you have not previously been vaccinated against hepatitis A and B we will offer these vaccines. We may also offer vaccination against HPV if you are eligible and have not had this in the past.

Follow up:

To ensure that the PEP has worked, and that you haven’t acquired any other infections, you will be offered some follow-up appointments for STI testing. These include:

  • Chlamydia and gonorrhoea testing 2 weeks after you start PEP (this can be done in clinic or as a home testing kit).
  • HIV and syphilis testing 45 days after you have finished your course of PEP.


Starting PrEP after you have finished your course of PEP ensures that you have continuous protection against HIV. If you are planning to start PrEP after you have finished your course of PEP we will see you before or on day 28 for HIV testing, and transition to PrEP. Depending on the type of risk you may also be advised to have a repeat test for syphilis after 3 months.

What if I am not given PEP?

PEP is not always required or recommended. If you are not given PEP following an assessment the reasons for this will be explained. We will help you make a plan to reduce your risk of acquiring HIV, and ensure you have space to discuss any concerns about STIs. We will also give advice about follow up testing and STI window periods.

Frequently asked questions (FAQs) about PEP

Do I need PEP if I’ve missed a dose of PrEP?

Taking PrEP offers excellent protection against HIV, but it needs to be taken as prescribed. If you have missed doses you may need PEP.

Missed doses when taking daily PrEP:

  • If you are using daily PrEP for anal sex only, you will need to take PEP if you have taken less than 4 doses of PrEP in the last 7 days.
  • If you are using daily PrEP for vaginal or frontal sex, you will need to take PEP if more than 48 hours have passed since your last PrEP dose, or you have taken fewer than 6 doses in the last 7 days.

Missed doses when taking event-based PrEP:

  • You may need PEP if you haven’t taken event-based PrEP exactly as prescribed (2-1-1 dosing).

How effective is PEP at preventing HIV infection after a risk?

There are limited clinical studies looking at the effectiveness of PEP, although it has been used for many years and is thought to reduce the risk of HIV acquisition by more than 95% if given as soon as possible after sex, and completed fully. It works by stopping any HIV that has entered the body from replicating. This means any cells infected with HIV will die before making new virus.

Are there any side-effects from taking PEP?

Most people tolerate PEP well and are able to finish the course without concerns. Some people experience nausea or diarrhoea when taking PEP. This usually settles after the first 2 weeks, and we can give medication to help with this.

If you develop flu-like symptoms while taking PEP, especially sore throat, high temperature or rash, it is important to contact us on 01273 523 388 for an urgent review with a sexual health clinician.

Can I stop taking PEP?

You can stop taking PEP at any point, although this may reduce the effectiveness of protection against HIV. If you are considering stopping due to side-effects, please contact us on 01273 523 388 to discuss this with a clinician as there are things we can do to help with this.

If the person you had sex with tests negative for HIV you may be advised to stop PEP as it is no longer necessary.

What do I do if I miss a PEP dose/take it late?

If you forget to take a dose, take it as soon as you remember it. However, if it is time for your next dose, skip the missed dose and go back to your regular schedule. Do not take a double dose to make up for a forgotten dose.

If it has been more than 48 hours since your last dose of PEP then you will need to stop taking it and seek advice from a sexual health clinician.

Can I have sex when I’m on PEP?

You can continue to have sex while on PEP, but it is important to consider the risk of acquiring other STIs. If you are further exposed to HIV during your PEP course, protection against HIV will continue unless the risk occurs in the 48 hours before finishing the course, in which case:

  • For anal sex PEP needs to be extended for a further 48 hours
  • For vaginal sex PEP needs to be extended for 7 days

If you have ongoing risk of acquiring HIV after finishing PEP we would recommend considering PrEP.

Can I take PEP after 72hrs?

There is no evidence that starting PEP after 72 hours gives any protection against HIV. After 72 hours, the HIV virus has entered the bloodstream and started to replicate in cells. Taking PEP will not stop this. We would recommend that you have testing for HIV in a clinic after 45 days if you believe you have been exposed to the virus.

Can I take PEP if I’ve been diagnosed with hepatitis B?

If you have been diagnosed with hepatitis B and take treatment for this, please let the clinician know, as this may affect the PEP treatment you are given.

Can I take PEP if I’m pregnant?

Although, like many medications, PEP is unlicenced for use during pregnancy, the overall risk of HIV transmission increases during pregnancy, so PEP would be recommended in circumstances where there has been a risk of exposure to HIV. A slightly different treatment may be prescribed so please let the clinician know if you could be pregnant.

Do I need PEP if the person I had sex with is HIV positive and undetectable?

You do not need PEP. Someone who has HIV and who is on effective treatment with an undetectable viral load cannot pass the virus on to anyone else.

Do I need PEP if I’m living with HIV?

PEP is only suitable for people who are not diagnosed with HIV. If you have been diagnosed with HIV we can offer access to HIV care and treatment.