Doxycycline after sex linked to STI decline in Australia
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Researchers at the Burnet Institute in Australia analysed health data and found that diagnoses of syphilis and chlamydia decreased among gay and bisexual men following the introduction of national guidance on using the antibiotic doxycycline after sex.
In September 2023, the Australasian Society for HIV, Viral Hepatitis and Sexual Health Medicine recommended that gay and bisexual men at higher risk of STIs consider taking doxycycline, known as doxyPEP, within 72 hours of sexual activity.
The study team reviewed data from over 78,000 men who attended sexual health clinics and general practices across Australia from January 2022 to December 2025. The analysis showed that syphilis diagnoses were 55% lower and chlamydia diagnoses 36% lower than expected, based on previous trends. Australia had experienced rising STI rates in the decade leading up to 2025, with nearly 6,000 syphilis diagnoses that year.
While these findings suggest doxyPEP can reduce STI rates in a larger population, researchers did not observe a significant decrease in gonorrhea diagnoses. The Burnet Institute collaborated with the Kirby Institute at UNSW Sydney and the National Reference Laboratory on this research, using data from a national surveillance system. The World Health Organization recently recommended targeted use of doxyPEP, alongside comprehensive sexual health care and monitoring for antibiotic resistance.
