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Post-exposure prophylaxis (PEP)

Post-exposure prophylaxis (PEP) is a treatment that can stop an HIV infection after the virus has entered a person’s body. It must be taken within 72 hours of exposure.

What is PEP?

PEP (sometimes called PEPSE) is a combination of HIV drugs that can stop the virus taking hold. It can be used after the event if you've been at risk of HIV transmission.

To work, PEP must be taken within 72 hours (three days), and ideally should be taken within 24 hours.

PEP is not a ‘morning after pill’ for HIV, and it’s not guaranteed to work. It’s meant as an emergency measure to be used as a last resort, such as if a condom fails during sex. Taking PEP will not protect you from other sexually transmitted infections or unplanned pregnancy.

Where to get PEP

PEP is available on the NHS for free, but is only given to people who meet guidelines about its use.

The best place to get PEP is a sexual health or HIV clinic. If you need PEP over the weekend or outside of office hours, when clinics will often be closed, the best place to go is an Accident and Emergency department.

PEP is not normally available from GPs.

As PEP is a powerful course of drugs, and is expensive to prescribe, you might be asked about:

  • the person you had sex with (and the chances that they had HIV)
  • what sort of sex you had (vaginal, oral or anal)
  • if the other person had HIV, what their viral load is.
  • If the person you had sex with is living with HIV and has an undetectable viral load, you will not need PEP as it won’t be possible for the virus to have been transmitted.

Once a doctor decides that it’s appropriate for you to have PEP, you will be asked to take an HIV test. This is to make sure you don’t already have HIV. If HIV is detected by a test, other forms of treatment will be recommended to you.

How to take PEP

PEP must be taken exactly as instructed and for 28 days. 

  • Do not skip a dose or fail to complete the full month as this makes it less likely to work.
  • Do not double a dose if you miss one.
  • If you do miss a dose and you remember in less than 24 hours, take the next one as soon as you remember.
  • If you miss more than 48 hours of PEP it will be discontinued.

The medication now used for PEP is a single tablet called Truvada and two tablets of raltegravir. 

Side effects from PEP are likely to be mild ones in the first few days, such as nausea, headaches or tiredness.

Do not take recreational drugs while on PEP as there can be dangerous interactions.

If you are pregnant or breastfeeding you can still take PEP.

If you're worried that you've been exposed to HIV, it might be well worth finding out more about HIV prevention pill PrEP (pre-exposure prophylaxis). It's available in some form in all UK countries and when taken as prescribed is almost 100% effective at preventing HIV transmission.

Commonly Asked Questions

Experts answer your questions on HIV, STIs and sexual health.