PrEP (pre-exposure prophylaxis)

PrEP (pre-exposure prophylaxis) is a drug taken by HIV-negative people before sex that reduces the risk of getting HIV.

How PrEP works

Taking PrEP before being exposed to HIV means there’s enough drug inside you to block HIV if it gets into your body – before it has the chance to infect you.

Taking PrEP

In clinical trials PrEP has been used in two different ways:

  • Taken regularly (one tablet per day).
  • Only taken when needed (two tablets two to 24 hours before sex, one tablet 24 hours after sex and a further tablet 48 hours after sex).

This second method is often called ‘on-demand’ or ‘event-based’ dosing.

Both methods have been shown to be very effective, although on-demand dosing has only been studied in gay and bisexual men.

Taking PrEP safely

If you’re thinking about getting PrEP from outside the NHS, it’s important that you talk to an adviser from a sexual health clinic. They will support you to use the treatment safely and provide necessary tests.

In most big PrEP studies, no one became infected if they took PrEP as recommended. But if you don’t take it correctly, it may not work.

The drugs used in PrEP are the same drugs that are prescribed to thousands of people living with HIV every year. They’re very safe and serious side effects are very rare.

A few people experience nausea, headaches or tiredness and, very rarely, the medication can affect kidney function. As a precaution, people taking PrEP have regular kidney function tests.

Although PrEP is highly effective at preventing HIV, it won’t protect you from other STIs or an unwanted pregnancy, which condoms would.

It’s important if you’re using PrEP that you go for regular STI screenings every three months.

Where to get PrEP

PrEP is only available for free from some sexual health clinics as part of the IMPACT trial in England.

Some people are also ordering generic versions of PrEP online. You can find more information from I Want PrEP Now.

PrEP and COVID-19

Should you still take PrEP during the COVID-19 lockdown? PrEP Lead Greg Owen answers frequently asked questions about taking PrEP during the coronavirus outbreak.

More information


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