DoxyPEP: doxycycline after sex to prevent syphilis and chlamydia

What is doxyPEP?

DoxyPEP is a prevention strategy for bacterial STIs: taking 200 mg of doxycycline, an old and well-known antibiotic, within 72 hours of condomless sex. The idea is to kill bacteria before they take hold.

Studies have shown a big drop in syphilis and chlamydia among men who have sex with men who use it. The effect is weaker on gonorrhoea, many strains of which already resist tetracyclines.

What does the French HAS recommend?

The French National Authority for Health (HAS) approved its recommendations in January 2025, with infectious disease specialists, GPs, dermatologists, Santé publique France and Act Up. In short:

• they only cover taking it after sex (not “doxy-PrEP” before);
• they target men who have sex with men and trans women highly exposed to STIs, for example with repeated bacterial STIs;
• prescribing is case by case, after discussion with a doctor, and should remain the exception rather than routine for everyone;
• every STI treated must be followed by a test of cure, to catch any doxycycline-resistant STIs.

Why so much caution?

Because taking an antibiotic often breeds resistance, in STIs but also in other bacteria in the body (skin, gut). WHO already considers gonorrhoea resistance a major threat. DoxyPEP is a useful tool for some people, not a mass solution.

What doxyPEP doesn’t do

• It doesn’t protect against HIV: that’s what PrEP and condoms are for.
• It doesn’t protect against hepatitis, HPV, herpes or mpox.
• It doesn’t replace testing every 3 months, which remains essential.

Side effects

Doxycycline can cause stomach upset and sun sensitivity (sunburn more easily). Take it with a large glass of water, not right before lying down.

What if I get it without a prescription?

Don’t. Poorly dosed, too-frequent self-medication, or taking it during an established STI, can mask an infection and create resistance. If you often get STIs, talk to your sexual health clinic or PrEP doctor: they can assess whether doxyPEP makes sense for you.