Comparing doxycycline use before and after sex to prevent STIs in men who have sex with men

Superiority of On-demand Pre-exposure Prophylaxis Versus Post-exposure Prophylaxis on Using Doxycycline for Preventing Sexually Transmitted Infections in Men Who Have Sex With Men

PHASE4 · Chinese University of Hong Kong · NCT06188442

This study is testing whether taking doxycycline before or after sex can help prevent bacterial STIs in men who have sex with men.

Quick facts

PhasePHASE4
Study typeInterventional
Enrollment300 (estimated)
Ages18 Years and up
SexMale
SponsorChinese University of Hong Kong (other)
Locations1 site (Shatin)
Trial IDNCT06188442 on ClinicalTrials.gov

What this trial studies

This clinical trial aims to evaluate the effectiveness of doxycycline taken as on-demand pre-exposure prophylaxis (DoxyODPrEP) versus its post-exposure use (DoxyPEP) in preventing bacterial sexually transmitted infections (STIs) such as chlamydia, gonorrhea, and syphilis among men who have sex with men (MSM). Participants will be randomly assigned to one of the two groups and will follow specific dosing schedules for doxycycline while attending regular clinical follow-ups over a 24-month period. The study will assess the incidence of bacterial STIs and the safety and acceptance of doxycycline within the MSM community.

Who should consider this trial

Good fit: Ideal candidates for this study are men who have sex with men, reside in Hong Kong, and are at risk of STIs.

Not a fit: Patients who are allergic to tetracycline class medicines or currently taking contraindicated medications may not benefit from this study.

Why it matters

Potential benefit: If successful, this study could provide a more effective method for preventing STIs in MSM, potentially reducing the incidence of these infections.

How similar studies have performed: Previous studies have explored similar approaches to STI prevention, but this specific comparison of DoxyODPrEP and DoxyPEP is novel.

Eligibility criteria

Show full inclusion / exclusion criteria
Inclusion Criteria:

* has had sex with another male in the past six months
* normally reside in Hong Kong
* can communicate in written and spoken Chinese or English
* willing and able to give written informed consent
* being willing and able to attend scheduled study clinic visits
* at risk of STI (had condomless sex with more than one man in the past 12 months, history of STI diagnosis in the past 12 months, inclination to have condomless sex, and other HIV-PrEP-eligible criteria)

Exclusion Criteria:

* Being allergic to tetracycline class medicines
* Currently taking medications that are contraindicated with doxycycline
* Using antibiotics for more than 14 days in the month preceding enrolment

Where this trial is running

Shatin

Study contacts

How to participate

  1. Review the eligibility criteria above with your treating physician.
  2. Visit the official trial page on ClinicalTrials.gov for the most current contact information and recruitment status.
  3. Contact the listed study coordinator or principal investigator to request pre-screening. Pre-screening is free and never obligates you to enroll.

View on ClinicalTrials.gov →

Conditions: Sexually Transmitted Diseases, Bacterial, Syphilis, Gonorrhea, Chlamydia, doxycycline, men who have sex with men, sexually transmitted infections

Last reviewed 2026-05-15 by the Find a Trial editorial team. Information on this page is for educational purposes and is not medical advice. Always consult qualified healthcare professionals about clinical trial participation.