The DoxyPEP study (United States, 2023)

The study that put doxyPEP on the map. Around 500 gay and bisexual men and trans women in San Francisco and Seattle took part. All used PrEP or lived with HIV, and all had had an STI in the past year.

Half of them used doxyPEP after sex, the other half did not. The results were so clear that the study was stopped early: in the doxyPEP group there were about two thirds fewer bacterial STIs. It was published in the New England Journal of Medicine.

The DOXYVAC study (France)

A French study among men who have sex with men who used PrEP found the same pattern: a strong drop in syphilis and chlamydia, and a smaller effect on gonorrhoea. Two large studies on two continents pointing the same way makes the result reliable.

The study among women (Kenya)

A study among young cisgender women in Kenya did not show a clear effect. Tests showed that many participants took the doses less often than planned, which makes it hard to draw conclusions. More in doxyPEP for women.

Why gonorrhoea lags behind

Neutral STI self-test kit on a table

Gonorrhoea bacteria have been exposed to many antibiotics over the years, and a large share is already resistant to tetracyclines, the group doxycycline belongs to. Where resistance is common, doxyPEP prevents fewer gonorrhoea infections. That is why regular testing stays important, also with doxyPEP.

Does it work outside a study?

After San Francisco started offering doxyPEP in 2022, the city saw fewer chlamydia and syphilis cases among the people who used it. Real-world figures from more cities are coming in.

How to get the most out of doxyPEP

Take it early

Ideally within 24 hours.

Full dose

Both tablets at once, 200 mg.

No dairy

2 hours before and after.

Keep testing

Every 3 months.

Frequently asked questions

How effective is doxyPEP?
In the large DoxyPEP study among gay and bisexual men and trans women, doxyPEP lowered the number of syphilis and chlamydia infections by more than three quarters and gonorrhoea by about half.
Does doxyPEP prevent gonorrhoea?
Partly. Many gonorrhoea strains are already resistant to tetracycline antibiotics, so doxyPEP prevents roughly half of gonorrhoea infections in studies, far less than syphilis and chlamydia.
Does doxyPEP work for women?
The one large study among cisgender women did not show a clear effect. Researchers think this was partly because many participants did not take the doses.
Does doxyPEP work if I take it late?
The studies used doses up to 72 hours after sex. Earlier is better, ideally within 24 hours. After 72 hours doxyPEP is not recommended.