References UK clinical guidance from the NHS, the British HIV Association (BHIVA), and the British Association for Sexual Health and HIV (BASHH). Last updated: April 2026.
Pre-exposure prophylaxis (PrEP) is HIV medication taken by people who are HIV-negative to prevent infection. The standard PrEP drug in the UK is Truvada (emtricitabine with tenofovir disoproxil) or a generic version. When taken as prescribed, PrEP reduces the risk of acquiring HIV through sex by over 99%.
PrEP is free on the NHS in England, Scotland, Wales and Northern Ireland through sexual health clinics. Here’s what you need to know about the benefits, the side effects, and the things to think through before starting.
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How PrEP Works
PrEP contains two drugs that block HIV from replicating if it enters your body. Taken regularly, it means that even if you’re exposed to HIV during sex, the virus cannot establish an infection. PrEP does not protect against other STIs or pregnancy — condoms and contraception are still important.
Benefits of PrEP
- Reduces HIV risk by over 99% when taken as prescribed
- Puts you in control of your own HIV prevention
- Reduces anxiety around sex for many people
- Protects both partners when one is HIV-negative
- Free on the NHS
- Can be stopped when no longer needed
Common Side Effects
Most people tolerate PrEP well. The most common side effects are mild and settle within a few weeks:
| Side Effect | How Often | When It Happens |
|---|---|---|
| Nausea | About 1 in 10 | First few weeks |
| Headache | Common | First few weeks |
| Tiredness or dizziness | Uncommon | Early on |
| Mild stomach upset | Common | Early on |
These usually settle. Taking PrEP with food often helps with nausea.
Longer-Term Considerations
Kidney function
Tenofovir DF can affect kidney function in a small number of people. You’ll have kidney blood tests before starting PrEP and every 3-6 months while taking it. Most changes are mild and reversible.
Bone density
Long-term PrEP may cause small reductions in bone mineral density. This is usually not clinically important but people with pre-existing bone problems should discuss with their clinician.
Drug resistance
If you start PrEP while unknowingly HIV-positive, the virus can develop resistance to the two drugs in PrEP. This is why all PrEP users are tested for HIV before starting and regularly afterwards.
Who Should Consider PrEP?
PrEP is offered through NHS sexual health clinics to people at higher risk of HIV, including:
- Men who have sex with men and their partners
- Trans people who have condomless sex
- Women and men who have condomless sex with HIV-positive partners not known to be undetectable
- People who inject drugs and share equipment
How to Get PrEP
Book an appointment at an NHS sexual health clinic. You’ll be tested for HIV, other STIs, and have kidney function checked. If PrEP is right for you, it’s prescribed free of charge. Follow-up is every 3 months.
Read more: What is HIV? | PrEP and drug resistance | Condoms and HIV
Frequently Asked Questions
Is PrEP 100% effective?
When taken as prescribed, PrEP reduces HIV risk by over 99%. Effectiveness depends on taking the pills correctly. Missed doses can reduce protection.
Do I need to take PrEP every day?
Most people take it daily. Event-based dosing (2-1-1) is an option for some men who have sex with men. Your clinic will help you decide which regimen suits your situation.
Are the side effects permanent?
No. The common side effects of nausea, headache and tiredness usually settle within a few weeks. Changes to kidney function or bone density usually reverse after stopping PrEP.
Related reading
- Choosing the Right PrEP Drug: Truvada vs Descovy
- Are HIV Tests Accurate If You're on PrEP, PEP or ART?
- Dovato for HIV: A Two-Drug Regimen
- Triumeq for HIV: A Straightforward Guide
- Efavirenz for HIV: An Older NNRTI Still in Use
Sources
- NHS — Sexual health conditions
- BASHH — UK clinical guidelines for STI management
- British HIV Association (BHIVA) — HIV treatment guidelines
- Terrence Higgins Trust — sexual health information
- UK Health Security Agency — STI surveillance data
Steve Page is a recognised expert on Sexually Transmitted Diseases (STDs) and STD treatments, having published numerous articles in peer-reviewed journals and presented his research at conferences around the world. He has an in-depth understanding of the latest medical research on STDs, and is an advocate for the development of new treatments and protocols to improve the health of those affected. In addition to his research, he has dedicated his career to understanding the causes and symptoms of STDs, as well as how to best treat those impacted.
