A ‘Morning-After Pill’ for Sexually Transmitted Infections Is Almost Here

Meanwhile, congenital syphilis—passed from mother to infant at birth, a sign that the pregnant person never received adequate prenatal care—caused 220 stillbirths and infant deaths in 2021, the last year for which there are national figures. Gonorrhea is gaining resistance to the last antibiotics currently available to treat it.

In medicine, prevention is almost always preferable to treatment: Vaccines and other prophylactic measures are less expensive, and can be planned in advance. So it has been a research goal to find uncomplicated prevention for STIs—something that, like the morning-after pill for pregnancy, can be taken a short time after sex and doesn’t rely on the user making decisions in the moment. 

The first test of doxyPEP, a small US trial that took place in 2011 and 2012, was published in 2015, and showed that HIV-positive men who took the post-exposure dose cut their rate of STIs by three-fourths. Fairly soon after that, social networks of men who have sex with men picked up on the findings, and began sharing knowledge about using preventive doxycycline off-label. A large 2017 French study of men using pre-exposure prophylaxis for HIV, known as PrEP, included within it a study of STI rates among men taking post-exposure doxycycline; it showed that doxyPEP could cut rates of syphilis and chlamydia infection by almost 70 percent. And last summer and this spring, the two largest international HIV conferences included presentations that confirmed the doses were successful in most circumstances.

Several of those presentations were drawn from the San Francisco and Seattle study just published in NEJM. Its results were so dramatic that the authors stopped the trial earlier than planned, in May 2022: They revealed that, among 501 men who were either living with HIV or taking HIV PrEP, consuming that single dose of doxycycline within 72 hours of sex without a condom reduced the combined incidence of the three major STIs by roughly two-thirds. 

“Our goal was to understand this in a real-world setting, in a heterogeneous population of people taking HIV PrEP but also living with HIV—which biologically aren’t different populations, but may be different in terms of sexual behaviors, sexual networks,” says Anne Luetkemeyer, one of the study’s principal investigators and a professor of medicine at the University of California, San Francisco. Combined with the French research, she adds, “we now have two studies that really showed very remarkably similar efficacy in this population.”

Those two sets of results may be enough to let doxyPEP enter mainstream medicine. In some places, it already has. Last October, San Francisco’s public health department became the first local department to support doxyPEP use in its jurisdiction. And after the NEJM paper, individual physicians tweeted they would begin prescribing doxyPEP because the results looked so solid—something they can do off-label because the Food and Drug Administration already approved the drug decades ago to treat a range of infections. 

When a new way of controlling a disease seems likely to enter the US mainstream, the CDC is expected to weigh in. So far, the agency hasn’t published official guidelines regarding the use of doxyPEP. Following the release of preliminary data at conferences, the CDC published “considerations for individuals and healthcare providers,” a strategy for sharing what’s known so far, as well as an acknowledgment that doxyPEP already is being used off-label. A CDC spokesperson told WIRED by email that formal draft guidance for physicians could come “by the end of the summer.”