PEP vs PrEP vs DoxyPEP: what's the difference?
PrEP prevents HIV before exposure. PEP prevents HIV after exposure. DoxyPEP lowers the risk of some bacterial STIs after sex. One table explains all three.
The names are confusingly close. The short version:
- PrEP = before. Medicine to prevent HIV, taken in advance.
- PEP = after. Emergency medicine to prevent HIV, started within 72 hours.
- DoxyPEP = after. An antibiotic to lower the risk of syphilis, chlamydia and gonorrhoea. Nothing to do with HIV.
If you think you’ve just been exposed to HIV, don’t read on. Go to the urgent page.
At a glance
| PrEP | PEP | DoxyPEP | |
|---|---|---|---|
| Stands for | Pre-exposure prophylaxis | Post-exposure prophylaxis | Doxycycline post-exposure prophylaxis |
| Protects against | HIV | HIV | Syphilis, chlamydia and, less well, gonorrhoea |
| When you take it | Before exposure, ongoing | After exposure, as an emergency | After sex |
| The deadline | Start ahead: about 7 days of daily pills for anal sex; 7 to 21 days for vaginal sex depending on the guideline | Start within 72 hours, ideally within 24 | Within 72 hours of sex, ideally within 24 |
| How you take it | A pill every day, on-demand pills around sex (for some people), or an injection every 2 or 6 months | Pills every day for 28 days | One 200 mg dose of doxycycline. No more than one dose in 24 hours |
| Type of medicine | HIV antiretrovirals | HIV antiretrovirals | A common antibiotic |
| Who it’s for | Anyone without HIV who may be exposed | Anyone without HIV after a possible exposure | Currently recommended for gay, bisexual and other men who have sex with men, and trans women, with a recent bacterial STI |
| How well it works | About 99% for sex when taken as prescribed | Very effective if started fast and completed; not a guarantee | In trials, cut syphilis and chlamydia by more than 70% and gonorrhoea by about half |
| Tests needed | HIV test before and every 3 months | HIV test before, and at 4–6 and 12 weeks after | STI and HIV tests every 3–6 months |
| Read more | What is PrEP? | What is PEP? | What is DoxyPEP? |
Which one do I need?
- “Something happened in the last three days and I’m worried about HIV.” That is PEP. Go now: urgent page.
- “I want ongoing protection from HIV.” That is PrEP.
- “I keep getting syphilis, chlamydia or gonorrhoea.” Ask about DoxyPEP.
- “I want to cover everything.” No single medicine does. PrEP plus DoxyPEP covers HIV and some bacterial STIs. Add condoms, vaccines (hepatitis A and B, HPV, mpox) and regular testing for the rest.
Things people mix up
PrEP doesn’t stop other STIs, and DoxyPEP doesn’t stop HIV. They are different medicines against different germs. One being in your bag says nothing about the other.
PEP is not “a stronger PrEP”. It’s a month-long emergency course that starts with an urgent clinic visit. If you find yourself needing PEP more than once, PrEP is the calmer option, and many clinics will move you from one to the other.
DoxyPEP is not the same as taking leftover antibiotics. The dose, the timing and who it’s recommended for come from clinical trials. Taking random antibiotics after sex doesn’t work and drives antibiotic resistance.
None of them is a morning-after pill. Emergency contraception is a separate medicine.
U=U is the fourth piece. If a partner has HIV and is on effective treatment with an undetectable viral load, they can’t pass HIV on through sex. That is prevention too.
Getting any of these abroad
On our clinic pages, each of these is listed separately, with the date we checked: PEP, PrEP — start here, PrEP refill and DoxyPEP. Availability differs a lot between countries, and DoxyPEP in particular is offered in some places and not others. Browse clinics by country. PrEP and DoxyPEP can also be ordered for delivery from PrEP Online; PEP cannot wait for a delivery, so for that go to a clinic or emergency department the same day.
Sources
Checked 19 September 2026.
- CDC, Preventing HIV with PEP and Preventing HIV with PrEP
- CDC, Doxy PEP for bacterial STI prevention and the 2024 clinical guidelines
- HIV.gov, Pre-exposure prophylaxis
Quick answers
What is the difference between PEP and PrEP?
Timing. PrEP is taken before a possible exposure to HIV, on an ongoing basis. PEP is a 28-day emergency course started within 72 hours after a possible exposure.
Does DoxyPEP prevent HIV?
No. DoxyPEP is an antibiotic that lowers the risk of syphilis, chlamydia and, to a lesser degree, gonorrhoea. It does nothing against HIV. PrEP and PEP do nothing against those bacterial infections.
Can I take PrEP and DoxyPEP together?
Yes, many people do. They are different medicines that protect against different infections. A clinician can prescribe both.
Read next
Where To Test is a directory, not a clinical service. Rules and prices change; every figure here links to its source and the date we checked. Spotted something out of date? Use “Something wrong? Tell us” on any clinic page.