Rising rates of syphilis, chlamydia, and gonorrhea have renewed interest in prevention beyond condoms. Doxycycline post-exposure prophylaxis, or doxy-PEP, is one of the newer tools.
The approach is straightforward: a 200 mg dose of doxycycline taken within 72 hours of condomless sex. In trials among gay and bisexual men and transgender women, it substantially reduced chlamydia and syphilis, with a smaller effect on gonorrhea.
In 2024 the CDC issued guidance supporting doxy-PEP for these higher-incidence populations, while emphasizing shared decision-making.
The caveats matter. Widespread antibiotic use raises legitimate questions about resistance and effects on the microbiome, so doxy-PEP is best offered thoughtfully, to those most likely to benefit, alongside testing and vaccination.