Sexually transmitted infection (STI) diagnoses have been rising steadily across the U.S. But over the last decade, there’s barely been any innovation to improve prevention or treatment. “There’s been a desperate need for something—or many things—to change the trajectory,” says Dr. Hyman Scott, a medical director at the San Francisco Department of Public Health.
In June 2024, the U.S. Centers for Disease Control and Prevention (CDC) announced that it endorsed a new way to keep people safe from STIs: a prophylactic dose of the common antibiotic doxycycline. The agency did so after Scott helped implement the regimen in San Francisco in 2022, providing a useful and effective case-study.
The strategy, called doxycycline post-exposure prophylaxis—or doxy-PEP—involves taking 200 mg of the common antibiotic doxycycline within 72 hours of unprotected sex (ideally, within 24 hours, Scott says). Research suggests that the regimen can lead to a 79% reduction in the risk of acquiring chlamydia, an 80% reduction in acquiring syphilis, and a 12% reduction in the risk of acquiring gonorrhea.
At the San Francisco Department of Public Health, “we give a prescription to people and give them instructions on how to use it, so they have it at home and don't need to contact their doctor when they need it,” Scott says. “We give them enough pills to cover the sex that they might have, and of course, if they need more, they can call for refills.” (Interested people in other parts of the country can ask their primary care doctors or local health clinics for a prescription.)
Doxycycline is appealing because “it’s a common medication that is generic and cheap,” Scott says. “It’s well-tolerated, safe, and used by lots of people, so it’s easily available. That's exactly the kind of prevention we want access to.”