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If you think you have been at risk of HIV infection then there is a treatment which might prevent HIV infection after the virus has entered the body.

This treatment is called PEP.

Post = after
Exposure = a situation where HIV has a chance to get into someone’s bloodstream
Prophylaxis = a treatment to stop any infection happening


PEP = a treatment to stop a person becoming infected with HIV after it’s got into their body.

PEP treatment only works if started as soon as possible and definitely within 72 hours of exposure, so act fast!

What is PEP?

PEP is a course of anti-HIV medication that needs to be taken for 4 weeks after any possible HIV infection. PEP can have side effects which can include; diarrhoea, nausea, and severe headaches.

HIV Infection

PEP will only be given if specialist doctors decide you are at a high risk for HIV infection; if doctors decide you are not at high risk then you will not receive PEP. Caution: PEP is NOT a substitute for condoms.

If you are unsure of your level of risk you can get information on how HIV is transmitted here.

How PEP works

If HIV gets into someone’s bloodstream it takes time before the virus permanently infects them. Starting PEP during this short period of time can kill the virus before this happens.

Act Fast!

PEP has the best chance of working the sooner it’s begun. Within 24 hours is best but it can be given up to 72 hours (3 days) after possible exposure. The longer the wait, the more chance PEP doesn’t work. After 72 hours PEP is unlikely to work at all so it’s not usually offered. Someone might get it if it’s a few hours after this deadline but not if it’s longer.

No guarantee

PEP isn’t guaranteed to work.

Some people take it and, for various reasons, it doesn’t work and they end up HIV positive. This is mostly because they:

  • Wait too long before taking it (starting within 24 hours is best)
  • Don’t take the pills for the full 28 days or exactly how the doctor tells them.

Where does someone get PEP in Leicester?

  • St Peter's Health Centre (Sexual health or ‘clap’ clinic)
  • Loughborough Health Centre
  • Leicester Royal Infirmary A&E department

Outside of Leicester these places might give people PEP:

  • Sexual health clinics (GUM/Clap clinics)
  • Hospitals (usually A&E or ‘Accident & Emergency’ departments)
  • If you already have HIV try your HIV clinic if the PEP is for someone you’ve had sex with

Not all these places in every part of the country will have PEP or be able to give it.

GPs won’t be able to prescribe PEP.

For more information about Leicester’s GUM Clinics click here.

Now there’s PEP does it matter so much if people don’t use condoms?

Here’s why PEP doesn’t change the need for condoms:

  • Using a condom is more likely to stop HIV being passed on than PEP
  • Condoms don’t make you ill with nasty side effects
  • You need a condom for as long as the sex lasts – but PEP has to be taken for 4 weeks
  • Condoms are everywhere. PEP can be hard – sometimes impossible – to get
  • You control getting hold of condoms but doctors decide if you should get PEP and they may say no

Frequently asked questions about PEP

So, on PEP someone won’t become HIV positive?
Research seems to show PEP makes infection with HIV a lot less likely. But PEP doesn’t work every time – some people who take it still end up with HIV afterwards. It can fail because some anti-HIV drugs don’t work against some strains of HIV. And it’s more likely to fail if it’s not taken properly or soon enough.

Does PEP have side effects?
Yes, it can cause diarrhoea, headaches, feeling sick and vomiting. Because of the side effects many people taking PEP need time off work or study. Some people have to stop taking PEP because of the side effects. Side effects go once someone stops taking the drugs. One Australian study showed among people taking PEP, side effects were mild to moderate for 2 out of 3 people and severe for 1 in 4.

What are the chances someone will get PEP?
New guidelines have been given to Sexual Health Clinics and hospitals that help doctors decide if PEP should be given. A doctor will need to ask questions about what kind of sex happened, when and who with.

It’s worth thinking about PEP if you or someone you had anal sex with didn’t use a condom or something went wrong with the condom and it’s not later than 72 hours (3 days) since it happened. Doctors might sometimes give PEP after oral sex, depending on the circumstances.

What kind of questions are asked if someone wants PEP?

Questions will be about:

  • The person the unsafe sex was with (to judge the chance that they had HIV or not)
  • The sex involved, e.g. when it happened, was it oral or anal sex, who penetrated who and did either of you come inside the other?
  • Having an HIV test. Before someone is given PEP they must have an HIV test to check they don’t already have HIV. They must also agree to be tested after taking PEP to see if it’s worked. PEP won’t be offered if someone refuses to be tested.

What if someone can’t get to a place that has PEP within 72 hours?
Once 72 hours are over PEP won’t usually be offered. So if it’s not possible to get to a Sexual Health clinic that’s open it may be worth trying a hospital Accident & Emergency department because they never close (although in hospitals other than the Leicester Royal Infirmary, there is no guarantee they’ll give PEP).

Is PEP a cure for HIV?
There’s no cure for HIV. PEP can only stop HIV infection if taken very early on after HIV’s entered the body, before the infection takes hold – within the first 72 hours (3 days).

Once HIV infection takes hold and the infection becomes permanent the anti-HIV drugs can’t get rid of HIV from the body. This is because the virus is now in parts of the body that the drugs can’t reach. So once HIV permanently infects someone the drugs can usually control the HIV in their body but can never get rid of it completely.

If someone’s taking PEP does that make them immune to HIV while they’re on it or once they’ve stopped taking it?
No. Unsafe sex while taking PEP could let more HIV into your body, making PEP much more likely not to work.

If after taking PEP someone’s stayed HIV negative and then has unsafe sex again, they can become infected just like any other HIV negative person.

If someone takes PEP can their body become resistant to HIV drugs so that the drugs won’t work if that person later gets HIV?
No, it’s the virus (HIV), not someone’s body that can become resistant to the drugs. If PEP works it gets rid of the virus – and the virus can’t become resistant because it’s not there anymore. So if someone were to get HIV later and needed drugs it wouldn’t make any difference that they took PEP in the past.

But if PEP doesn’t work and a person then ends up infected, there may be problems with the HIV in the body being resistant to some drugs, including ones used in PEP.

How many times can someone have PEP?
Doctors decide who gets PEP and they’re unlikely to give these expensive and powerful drugs to the same person time after time. So someone who keeps having unsafe sex will usually be offered help with having safer sex and won’t be given PEP lots of times. Besides, the side effects often put people off wanting to take PEP more than once.

If one day I feel I (or someone I’ve had sex with) might have been at risk of getting HIV what can I do?
Email: or call Trade on 01162541747. Both can help you decide if it’s worth thinking about asking for PEP.

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