PrEP is a drug taken by HIV-negative people before and after 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.

The medication used for PrEP is a tablet which contains tenofovir and emtricitabine (drugs commonly used to treat HIV). It is sometimes called Truvada but most of the PrEP we use in the UK is generic PrEP.

Different PrEP delivery methods such as injectables and implants are being researched. As well as PrEP tablets, PrEP vaginal rings will be available soon.

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.

Daily dosing is recommended for women who need to take PrEP every day for seven days to be protected against HIV.

Daily PrEP is recommended for all trans people using hormone treatment as there isn’t sufficient data to support other dosing options.

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 unplanned pregnancy, which condoms can.

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

Where to get PrEP in Hertfordshire


PrEP is now available free on the NHS in England from sexual health clinics. If you are interested in getting PrEP in Hertfordshire, please contact Sexual Health Hertfordshire on 0300 008 5522 to make an appointment with a health advisor. You can use our service finder to find your nearest service.

We can also refer clients for PrEP. Contact our Hertfordshire team to find out more about our Fast Track to PrEP service.