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.
PrEP and PEP are two medication-based strategies for preventing HIV. PrEP is taken before potential exposure to stop infection happening. PEP is taken after a possible exposure as emergency prevention. Both are free on the NHS and highly effective when used correctly.
Here’s how they compare and how to access them.
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PrEP vs PEP at a Glance
| Feature | PrEP | PEP |
|---|---|---|
| Full name | Pre-exposure prophylaxis | Post-exposure prophylaxis |
| When taken | Before exposure (ongoing) | After exposure (emergency) |
| Time window | Must be established before sex | Must start within 72 hours |
| Duration | Ongoing while at risk | 28-day course |
| Drug | Truvada (emtricitabine/tenofovir) | Usually 3-drug ART regimen |
| Effectiveness | Over 99% when taken correctly | Very high if started promptly |
| Where to get it | Sexual health clinics | Sexual health clinics or A&E |
| Cost | Free on NHS | Free on NHS |
PrEP in Detail
PrEP is for people who are HIV-negative and at ongoing risk. It’s taken either daily or on-demand (2-1-1 schedule for MSM). You need:
- A confirmed negative HIV test before starting
- Regular follow-up every 3 months (HIV test, STI screen, kidney check)
- To take it consistently for maximum protection
PEP in Detail
PEP is emergency HIV prevention after a specific exposure. You should seek PEP if:
- You’ve had condomless sex with someone who may have HIV
- A condom broke during sex with someone of unknown status
- You’ve been sexually assaulted
- You’ve had a needlestick injury
- You’ve shared injecting equipment
PEP must be started within 72 hours — the sooner the better. It’s a 28-day course of antiretroviral medication. Access it through:
- Sexual health clinics (during opening hours)
- A&E departments (out of hours)
Which Do You Need?
- Ongoing risk (regular condomless sex, multiple partners) → PrEP
- One-off incident (condom broke, unexpected exposure) → PEP
- Both — if you’re not yet on PrEP and have a recent exposure, start PEP now and discuss transitioning to PrEP afterwards
Read more: PrEP benefits and risks | How to get PrEP | What is HIV?
Frequently Asked Questions
Can I get PEP from my GP?
PEP is usually provided by sexual health clinics or A&E. GPs don’t typically prescribe it because of the urgency and specialist assessment required.
If I’m on PrEP, do I still need PEP?
If you’re taking PrEP consistently, you’re already protected and don’t need PEP. If you’ve missed PrEP doses and had a risky exposure, seek clinical advice.
Is PEP the same as the morning-after pill?
It’s a similar concept — emergency prevention after the event — but PEP is a 28-day course of HIV medication, not a single dose.
Related reading
- Are HIV Tests Accurate If You're on PrEP, PEP or ART?
- Can Condoms Protect Against HIV?
- Choosing the Right PrEP Drug: Truvada vs Descovy
- Why Is an HIV Prevention Vaccine So Difficult to Develop?
- Do Condoms Prevent STIs?
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.
