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Can post-exposure prophylaxis (PEP) stop me getting HIV?

Post-exposure prophylaxis (PEP) may stop you developing an HIV infection if you've been exposed to the virus. However, it doesn't always work.

You may have been exposed to HIV if you've: 

  • had unprotected sex (without using a condom)
  • had sex with someone with HIV and the condom broke
  • been injured with an HIV-infected needle

What is PEP?

PEP is a course of anti-HIV medication. You must start the treatment as soon as possible after you've been exposed to HIV, ideally within a few hours. The medicines must be taken every day for 28 days (4 weeks).

PEP is unlikely to work if it's started after 3 days (72 hours) and it won't usually be prescribed after this time. It is best to start taking PEP within 1 day (24 hours) of being exposed to HIV.

PEP makes infection with HIV less likely. However, it's not a cure for HIV and it doesn't work in all cases.

Also, the treatment may not work if you:

  • take the medicines incorrectly
  • don't start taking the medicines soon enough

What are the side effects of PEP?

PEP can cause side effects in some people, such as:

They usually start to get better as you keep taking PEP.

Where can I get PEP?

PEP is only available on prescription. You can get PEP from:

However, PEP may not be available in all areas of England. GPs can't usually prescribe PEP.

Find your nearest GUM clinic 

Find your nearest A&E department

When you request to have PEP, you'll be asked some questions, such as:

  • who you had sex with, to assess your risk of exposure to HIV
  • whether you had oral, vaginal or anal sex
  • whether the other person definitely had HIV – and if known, what was their "viral load"

If a doctor decides you are not at risk of having HIV from your answers they will not prescribe PEP.

PEP and HIV tests

You'll be asked to take an HIV test before starting PEP treatment, to check whether you already have HIV. If you don't agree to an HIV test, you won't be given PEP.

You'll also need an HIV test after the treatment, to check that it's been successful.

Safe sex

HIV can't be cured. Don't rely on PEP to prevent HIV, because it doesn't always work.

Using a condom is the best way to prevent the spread of sexually transmitted infections (STIs), including HIV.

Read the answers to more questions about sexual health.

Further information

Page last reviewed: 19 September 2018
Next review due: 19 September 2021