STI Risk Reduced With Post-Sex Doxycycline in Men Who Have Sex With Men

Studies suggest that the incidence of bacterial sexually-transmitted infections (STIs) is on the rise among men who have sex with men (MSM). However, new research shows that taking doxycycline, an antibiotic, within 72 hours after condomless sex could lower the risk.

The study, which was presented in February at the 2017 Conference on Retroviruses and Opportunistic Infections, included 232 MSM who were considered high risk for developing STIs. All of the men were participants in a trial for an on-demand HIV prevention protocol.

The men were divided into two groups of 116 each. One group was told to take two 100 mg pills of the doxycycline within 72 hours of condomless sex, but not more than 6 pills weekly. The other group did not take doxycycline. Both groups were counseled on safe sex practices and given condoms. All participants were tested for syphilis, gonorrhea, chlamydia, and HIV every eight weeks with a median follow-up period of 8.7 months.

Thirty-one percent of the men overall – 24% of the doxycycline group and 39% of the no-doxycycline group - developed an STI. Seventy-one percent of the STIs were asymptomatic.

Rates of syphilis and chlamydia were lower for the doxycycline group, but gonorrhea rates were similar:

  Doxycycline Group No-Doxycycline Group
Syphilis 3 men 10 men
Chlamydia 7 men 21 men
Gonorrhea 25 men 22 men

Eight men in the doxycycline group left the study because of gastrointestinal adverse events, which affected 53% of this group as a whole. Forty-one percent of the men without treatment reported similar adverse events.

Overall risk of STIs decreased 47% for the doxycycline group. However, the authors noted that more research is needed to determine how this approach would work in the long term. The authors also suggested further research on the role of antibiotic resistance.



Newman, Emily
“Research shows 47% reduction in STIs among gay men who took doxycycline after sex”
(February 16, 2017)

Conference on Retroviruses and Opportunistic Infections 2017

Molina, Jean-Michel, et al.
“On Demand Post Exposure Prophylaxis with Doxycycline for MSM Enrolled in a Prep Trial”
(Abstract 91LB. Presented February 16, 2017)

Medscape Medical News

Boerner, Heather
“Antibiotics After Sex Nearly Halves Incidence of STIs”
(February 16, 2017)