DoxyPEP May Be Losing Its Edge Against Gonorrhea, New Study Finds

A study published May 7, 2026 in The Lancet Infectious Diseases reports that doxycycline post-exposure prophylaxis, commonly called doxyPEP, may be losing its effectiveness against gonorrhea in Southern California, even as protection against chlamydia and syphilis appeared to hold. The decline was linked to the rapid spread of tetracycline-resistant gonorrhea strains in the local circulating bacterial population.

DoxyPEP is the practice of taking a single 200 mg dose of doxycycline within 72 hours after condomless sex to reduce the chance of acquiring a bacterial sexually transmitted infection. The U.S. Centers for Disease Control and Prevention issued formal guidance supporting doxyPEP for certain populations in 2024. The new study, funded by the CDC and based in the Kaiser Permanente Southern California integrated health-care system, is one of the first large real-world looks at how durable that protection is once doxyPEP enters routine clinical use.

What the study found

The researchers used a retrospective, test-negative observational design. Of 33,118 individuals who met eligibility criteria, 26,582 had one or more STI tests between January 1, 2023 and June 30, 2025 and were included in the primary analyses. Within that group, 2,262 people, or 8.5%, received one or more doxycycline PEP fills.

Across the full study period, the preventive effectiveness estimates were:

Chlamydia: 66.5%, 95% CI 53.6 to 75.9 Gonorrhea: -1.8%, 95% CI -18.5 to 12.5 * Syphilis: 60.7%, 95% CI 28.3 to 78.5

The gonorrhea picture was not static. Effectiveness against gonorrhea declined from 42.3% (95% CI 2.7 to 65.8) before statewide doxycycline PEP implementation to -15.0% (95% CI -51.1 to 11.4) between January and June 2025. The authors reported that this decline was associated with a rapid increase in the prevalence of tetM, a tetracycline-resistance gene, in circulating Neisseria gonorrhoeae lineages.

The study authors interpret these results as a rapid loss of doxyPEP effectiveness against gonorrhea within the first year after implementation in MSM and transgender women in Southern California, while effectiveness against chlamydia and syphilis remained sustained.

Why it matters for testing

The headline-friendly version of this finding is that doxyPEP no longer works against gonorrhea. The more careful version is that doxyPEP may not be durable protection against gonorrhea in settings where tetracycline-resistant strains are spreading. Those are different claims, and the distinction matters for anyone making decisions based on this study.

The practical takeaway is not that doxyPEP is useless. It is that gonorrhea can still require testing and attention even when doxyPEP is part of someone's prevention plan. People using or considering doxyPEP should follow clinician or public-health guidance for STI testing.

For readers who want to check current chlamydia and gonorrhea status, LabTestSuperstore offers a chlamydia and gonorrhea test that can be ordered online and completed at a participating lab without an appointment.

What not to overread

A few important limits on this finding:

The study is retrospective and observational, not a randomized controlled trial. The setting is one integrated health system in Southern California. Results may not generalize to other regions, other populations, or other resistance backgrounds. The eligible cohort focuses on MSM and transgender women, the groups most studied in doxyPEP research to date. Confidence intervals on the post-implementation gonorrhea effectiveness estimate cross zero, which is what the authors are describing when they say protection has been lost. The loss of effectiveness was associated with rising tetM* prevalence in circulating gonorrhea strains. The study does not claim that doxyPEP use in any individual patient caused resistant gonorrhea in that patient.

This is also not a statement about doxyPEP's effect on chlamydia or syphilis in this study, where protection held up.

The bottom line

DoxyPEP's protection against gonorrhea is the part of the doxyPEP story that looked weakest going in, and this Southern California data set strengthens the case for caution. Chlamydia and syphilis protection in this study held. Gonorrhea testing remains a relevant part of sexual health screening for people in groups where it is indicated, with or without doxyPEP. For background on related symptoms and conditions, see our pages on chlamydia symptoms and STD symptoms.