The short answer
A pill you take before any risk.
PrEP (pre-exposure prophylaxis) is a prescription medicine for people who don’t have HIV. Taken as prescribed, it lowers the chance of getting HIV from sex by about 99%, because the medicine is already in your body if the virus ever gets in.
Most people take one pill a day. Some people who only have anal sex use an on-demand schedule called 2-1-1. Either way, you start with a quick HIV test and come back every three months for a check-up and a refill.
PrEP in five facts
- Who it’s forAnyone who is HIV-negative and could be exposed to HIV.
- What’s in itTwo HIV medicines, tenofovir and emtricitabine, in one pill.
- When it worksAbout 7 days for anal sex and 21 days for vaginal or front-hole sex on daily pills.
- What it doesn’t doIt doesn’t prevent other STIs or pregnancy.
- How you stay on itAn HIV test and a refill every three months.
How it works
What PrEP does inside your body.
The medicine builds up
With each daily pill, the two medicines collect in the cells where HIV usually enters, such as the lining of the rectum, vagina and cervix. Rectal tissue reaches protective levels faster, which is why anal sex is covered sooner.
HIV can’t copy itself
If HIV gets into the body, it needs to copy its genetic material to take hold. The medicines in PrEP block that step, so the virus can’t set up an infection.
Protection lasts while you keep taking it
PrEP isn’t a vaccine. If you stop taking it, the medicine levels fall and protection fades, so talk to a doctor before you stop or restart.
See your own dates in the PrEP planner, or read how long PrEP takes to work.
Two schedules
Daily or 2-1-1?
It’s the same pill either way. A doctor helps you choose, based on the kind of sex you have, how often, and your hepatitis B result.
| Daily PrEP | On-demand 2-1-1 | |
|---|---|---|
| How you take it | One pill every day | 2 pills 2–24 h before sex, then 1 at 24 h and 1 at 48 h |
| Type of sex | Any | Anal sex only |
| Hepatitis B or oestradiol | Suitable, with advice | Not suitable |
| Full protection | Day 7 (anal), day 21 (vaginal) | From the double dose, if timed right |
| Best for | Regular or unplanned sex | Occasional sex you can plan |
More detail: how on-demand 2-1-1 PrEP works and what to do if you miss a PrEP dose.
Who it’s for
PrEP isn’t only for gay men.
Women, straight men, trans and non-binary people, couples where one partner has HIV, and anyone who doesn’t always use condoms can all use PrEP. The schedule may differ, but the protection is the same.
Safety
Is PrEP safe?
PrEP has been used by millions of people. Most feel nothing at all; a few have mild stomach upset or headaches in the first weeks. Kidney function and hepatitis B are checked before you start, and kidneys are monitored over time.
PrEP vs PEP
PrEP is taken before any risk, for as long as you need it. PEP is a 28-day emergency course started within 72 hours after a possible exposure. If that’s you, act today: get urgent PEP advice.
PrEP and STIs
PrEP only prevents HIV. Syphilis, gonorrhoea and chlamydia can still pass on, so condoms and regular STI checks still matter, and many STIs have no symptoms.
Today could be day one.
Send one message and we’ll take it from there: tests, plan and pills, in a single visit.