Daily, Weekly, or Event-driven Doxycycline for STI Prevention Among Men Who Have Sex With Men (MSM) Engaging in Chemsex: The DOSE Non-inferiority Trial (DOSE)

November 3, 2026 updated by: Cherie Blair, MD, PhD, University of California, Los Angeles

The goal of this clinical trial is to learn if three different dosing strategies of doxycycline (daily, weekly, and on-demand) works to prevent sexually transmitted infections (gonorrhea, chlamydia, and syphilis) among men who use methamphetamine and who have sex with other men. The main question it aims to answer is:

Does daily, weekly, and on-demand doxycycline dosing strategies lower the incidence of quarterly STIs (gonorrhea, chlamydia, and syphilis)?

Participants will:

Take doxycycline either on-demand (within 72 hours after sex), daily, or weekly doxycycline for one year Visit the clinic once every 3 months to complete questionnaires, undergo HIV/STI testing, and collect samples. Additional visits may be needed to receive STI treatment.

Complete text surveys once every month

Study Overview

Status

Not yet recruiting

Conditions

Intervention / Treatment

Detailed Description

This study will evaluate the acceptability, effectiveness, and adherence of alternative doxycycline dosing strategies to optimize STI prophylaxis in this high-risk population. We will accomplish this through the following independent, yet interrelated Aims: 1) Determine effectiveness of fixed-dose daily, fixed-dose weekly, and event-driven dosing of doxycycline for STI prophylaxis; 2) Assess acceptability and preferences for doxycycline as STI prophylaxis through either fixed dose (daily or weekly) or event-driven (post-exposure) dosing strategies through individual interviews; 3) Evaluate and compare adherence and tolerability of daily, weekly, and event-driven doxycycline dosing strategies. We will conduct an open-label, non-inferior, randomized control trial (RCT) comparing fixed-dose daily, fixed-dose weekly, and event-driven doxycycline dosing strategies on quarterly incidence of STIs among MSM who use MA. We will screen 900 individuals to recruit a cohort of 300 MSM who self-report MA use in conjunction with condomless anal intercourse in the past month. At the Enrollment visit, participants will receive HIV, syphilis, and gonorrhea/chlamydia (GC/CT) testing as well as complete demographic and behavioral questionnaires. Enrolled participants will be randomly assigned 1:1:1 to either fixed-dose daily doxycycline (100mg daily; n=100), fixed-dose weekly doxycycline (200mg weekly; n=100), or event-driven doxyPEP (200mg taken up to 72 hours after a potential STI exposure; n=100; standard of care). All participants will participate in Quarterly follow-up visits where they will be assessed for HIV, bacterial STIs (GC/CT and syphilis), adherence to doxycycline, sexual behaviors/practices, substance use, nasal Staph aureus colonization and doxycycline resistance over 12 months. The primary outcome for this study will be quarterly incidence of, GC, CT, and/or early syphilis (defined as newly positive rapid plasma reagin [RPR] or four-fold rise in RPR titers), by arm.

Study Type

Interventional

Enrollment (Estimated)

300

Phase

  • Phase 4

Contacts and Locations

This section provides the contact details for those conducting the study, and information on where this study is being conducted.

Study Contact

Study Locations

  • United States
    • California
      • Los Angeles, California, United States, 90038
        • UCLA Vine Street Clinic
        • Contact:

Participation Criteria

Researchers look for people who fit a certain description, called eligibility criteria. Some examples of these criteria are a person's general health condition or prior treatments.

Eligibility Criteria

Ages Eligible for Study

18 years and older (Adult, Older Adult)

Accepts Healthy Volunteers

No

Genders Eligible for Study

Male

Description

Inclusion Criteria:

  • Born male
  • Age ≥ 18 years old
  • Reports receiving an STI diagnosis (i.e., GC, CT, and/or syphilis) in the past 12 months
  • Reports MA use in conjunction with CAI with a male partner in the 30 days prior to screening
  • Not planning to relocate out of the study area in the 12-month follow-up period
  • Willingness to engage in up to one year of repeated antibiotic exposure
  • Willing and able to give written informed consent

Exclusion Criteria:

  • Reported allergy to tetracyclines
  • Current or anticipated use of a medication that interacts with doxycycline (prohibited medications listed below)
  • Current or planned use of doxycycline for a prolonged period (> 2 weeks, with the exception of pre-enrollment doxyPEP)
  • Prolonged antibiotic use (> 2 weeks, with the exception of pre-enrollment doxyPEP) in the 30 days prior to study enrollment
  • Co-enrollment in any other concurrent study that may interfere with this study, such as an STI prevention trial, unless approved by the PI or designee
  • Any other medical or psychiatric condition that, in the opinion of the PI or designee, may interfere with study participation or participant safety

Study Plan

This section provides details of the study plan, including how the study is designed and what the study is measuring.

How is the study designed?

Design Details

  • Primary Purpose: Prevention
  • Allocation: Randomized
  • Interventional Model: Parallel Assignment
  • Masking: None (Open Label)

Arms and Interventions

Participant Group / Arm
Intervention / Treatment
Experimental: On-demand doxycycline

Participants randomized to on-demand doxycycline will be instructed to take doxycycline hyclate 200mg once as needed within 24 and up to 72 hours after sex (not to exceed 200mg in 24 hours).
Drug: On demand doxycycline hyclate 200mg

Participants randomized to receive on-demand doxycycline hyclate 200mg will be instructed to take doxycycline hyclate 200mg once as needed within 24 hours and up to 72 hours after sex (not to exceed 200mg in 24 hours)
Experimental: Weekly doxycycline

Participants randomized to receive fixed dose weekly doxycycline hyclate 200mg will be instructed to take doxycycline hyclate 200mg once weekly, regardless of sexual exposure.
Drug: Weekly doxycycline hyclate 100mg

Participants randomized to receive weekly doxycycline hyclate 100mg will be instructed to take doxycycline hyclate 100mg once weekly
Experimental: Daily doxycycline

Participants randomized to receive fixed dose daily doxycycline hyclate 100mg will be instructed to take doxycycline hyclate 100mg once daily, regardless of sexual exposure.
Drug: Daily doxycycline hyclate 100mg

Participants randomized to receive fixed dose daily doxycycline hyclate 100mg will be instructed to take doxycycline hyclate 100mg once daily

What is the study measuring?

Primary Outcome Measures

Outcome Measure
Time Frame
Quarterly incidence of chlamydia, gonorrhea, and/or early syphilis infection
Time Frame: Quarterly incidence of C. trachomatis, N. gonorrhoeae, and/or early syphilis infection by laboratory-based diagnosis (over 1 year time period)
Quarterly incidence of C. trachomatis, N. gonorrhoeae, and/or early syphilis infection by laboratory-based diagnosis (over 1 year time period)

Collaborators and Investigators

This is where you will find people and organizations involved with this study.

Sponsor

University of California, Los Angeles

Collaborators

National Institute on Drug Abuse (NIDA)

Investigators

  • Principal Investigator: Cherie Blair, MD, PhD, University of California, Los Angeles

Study record dates

These dates track the progress of study record and summary results submissions to ClinicalTrials.gov. Study records and reported results are reviewed by the National Library of Medicine (NLM) to make sure they meet specific quality control standards before being posted on the public website.

Study Major Dates

Study Start (Estimated)

November 1, 2026

Primary Completion (Estimated)

June 30, 2030

Study Completion (Estimated)

June 30, 2031

Study Registration Dates

First Submitted

November 3, 2026

First Submitted That Met QC Criteria

November 3, 2026

First Posted (Actual)

November 9, 2026

Study Record Updates

Last Update Posted (Actual)

November 9, 2026

Last Update Submitted That Met QC Criteria

November 3, 2026

Last Verified

November 1, 2026

More Information

Terms related to this study

Keywords

Additional Relevant MeSH Terms

Other Study ID Numbers

  • 26-1595
  • 1R01DA066392-01A1 (U.S. NIH Grant/Contract)

Plan for Individual participant data (IPD)

Plan to Share Individual Participant Data (IPD)?

YES

Drug and device information, study documents

Studies a U.S. FDA-regulated drug product

Yes

Studies a U.S. FDA-regulated device product

No

product manufactured in and exported from the U.S.

No

This information was retrieved directly from the website clinicaltrials.gov without any changes. If you have any requests to change, remove or update your study details, please contact register@clinicaltrials.gov. As soon as a change is implemented on clinicaltrials.gov, this will be updated automatically on our website as well.

Subscribe