Doxy-PEP: doxycycline after sex
Taking doxycycline within 72 hours of sex cuts bacterial STI rates substantially in some groups — and not in others. What the trials found and where the uncertainty sits.
Doxy-PEP means taking a single 200 mg dose of doxycycline within 72 hours after condomless sex, to prevent bacterial STIs. It is not a treatment and does nothing for HIV.
What the trials found
- *DoxyPEP (Luetkemeyer et al., NEJM, 2023) — San Francisco and Seattle, men who have sex with men and trans women, all with a recent STI. Quarterly STI incidence fell by about two-thirds*: roughly 65% reduction overall, with chlamydia and syphilis reduced by around 70–80% and gonorrhoea by about 55%.
- ANRS DOXYVAC (France, 2023) — similar magnitude of benefit for chlamydia and syphilis; gonorrhoea reduction was smaller and less durable.
- *dPEP Kenya (Stewart et al., NEJM, 2023) — cisgender women taking HIV PrEP. No significant reduction* in STI incidence. Hair-sample testing showed low adherence in many participants, so the trial does not prove doxy-PEP cannot work for women, but it does mean benefit in this group is unproven.
Current guidance
CDC issued formal clinical guidelines in June 2024 recommending doxy-PEP be offered to men who have sex with men and to transgender women who have had a bacterial STI in the past 12 months, as part of a shared decision with a clinician. BASHH and UKHSA published UK guidance in 2025 taking a more cautious line, recommending it for a narrower group with repeated bacterial STIs.
No guideline currently recommends doxy-PEP for heterosexual men or cisgender women, because the evidence is absent rather than negative.
Dose and use
- 200 mg doxycycline, ideally within 24 hours and no later than 72 hours after condomless oral, anal or vaginal sex.
- Maximum 200 mg in a 24-hour period regardless of how many encounters.
- Take with a full glass of water, sitting upright, and avoid lying down for 30 minutes — doxycycline can cause oesophageal irritation.
- Photosensitivity is common; use sun protection.
- Contraindicated in pregnancy and while trying to conceive, and in children under 8.
Doxy-PEP does not replace condoms, PrEP, vaccination or testing. People using it should still test for STIs at least quarterly, including throat and rectal sites, and be up to date with HPV, hepatitis A/B and — where offered — meningococcal B vaccination, which the 2024 4CMenB studies suggest gives partial protection against gonorrhoea.
The resistance question
This is the genuine open problem. Doxycycline is a tetracycline, and tetracycline resistance in N. gonorrhoeae is already widespread — which explains the weaker gonorrhoea effect. Trial follow-up has shown increases in tetracycline-resistant Staphylococcus aureus carriage among users. Effects on the gut microbiome and on population-level resistance over years are not yet known, and both CDC and BASHH recommend ongoing resistance surveillance as a condition of use. Anyone considering doxy-PEP should weigh a clear short-term individual benefit against an uncertain longer-term collective cost.
When to see a clinician
Doxy-PEP is prescription-only and should be started through a sexual health service that can also test you regularly. Seek care sooner for any new sore, discharge or rash rather than assuming doxy-PEP has covered it.
Sources
- Luetkemeyer AF et al., New England Journal of Medicine, 2023 (DoxyPEP trial).
- Molina JM et al., ANRS DOXYVAC, presented IAS 2023; Lancet Infectious Diseases, 2024.
- Stewart J et al., New England Journal of Medicine, 2023 (dPEP Kenya).
- CDC, Guidelines for the Use of Doxycycline Post-Exposure Prophylaxis, June 2024.
- BASHH/UKHSA doxycycline PEP position statement, 2025.
Educational reference, not medical advice. Every article is community-edited and cites its sources; verify anything that affects your health with a clinician who knows your history.