Clinical trials documented the efficacy of doxycycline post-exposure prophylaxis (Doxy PEP) in preventing syphilis, gonorrhea, and chlamydial infection. More recent studies raise uncertainties about the level of protection against gonorrhea.
The latest analysis comes from Seattle-King County, which found that tetracycline resistance had increased among MSM with N. gonorrhoeae infection in Seattle. Read the details in Potential Impact of Doxycycline Post-Exposure Prophylaxis on Tetracycline Resistance in Neisseria gonorrhoeae and Colonization with Tetracycline-Resistant Staphylococcus aureus and Group A Streptococcus, published in Clinical Infectious Diseases (2/28/25).
A January 2025 study from San Francisco found that Doxy PEP use was associated with significant declines in cases of chlamydia and early syphilis but not gonorrhea. See DoxyPEP Study in SF: STI Case Declines but Not Gonorrhea.
See Doxy PEP for Bacterial STI Prevention for resources on Doxy PEP.