Pre-exposure prophylaxis (PrEP) is a way to protect against HIV infection. It involves taking a pill regularly before and after sex. PrEP is meant for people who don't have HIV to keep them from getting it. The pill used for PrEP is an antiretroviral drug, which is the same kind of pill taken by those who already have HIV to treat the virus.

Español — ¿Que es la PrEP?
Português — O que é PrEP?

Does PrEP work and how does it work?

Studies from around the world have shown that taking a daily pill called PrEP can greatly reduce the risk of getting HIV. PrEP works by stopping HIV from entering and multiplying in the body's cells. This means that even if you are exposed to HIV, the medication can help prevent you from contracting HIV. To make sure PrEP is effective, it's important to take the pill every day as directed.

PrEP can be used by everyone

PrEP in a pill formulation (Truvada and its generic versions) has been tested in lots of groups of people - including cis and trans women. Decsovy and its generic formulations has only been tested in cis gay men and trans women and so we don't yet know if it works in cis women.

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

  • taken regularly (one tablet per day).
  • only taken when needed (two tablets 2 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.

As mentioned above, both methods have been shown to be very effective, although on-demand dosing has only been studied in cis men.

Therefore, daily dosing is recommended for cis women and trans people, meaning that they need to have been taking PrEP every day for seven days to be protected against HIV and continue to use it after exposures.

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

If you have a partner with HIV and are considering getting pregnant, you can take PrEP if you’re not already taking it. PrEP may be an option to help protect you and your baby from getting HIV while you try to get pregnant, during pregnancy, or while breastfeeding.

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. 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 would.

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

PrEP is available free on the NHS in England from sexual health clinics.

NHS Sexual Health Clinics are available and safe to access no matter your immigration status. The only information they will ask is your name, your date of birth and a phone number to make an appointment.

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