Worried about the risky sex you had last night?

Using a common antibiotic following sex can dramatically reduce a person’s risk of some sexually transmitted infections (STIs), a new study says.

Taking doxycycline within 72 hours after sex reduced risk of chlamydia by 79%, syphilis by 80%, and gonorrhea by 12%, results published in JAMA Internal Medicine show.

This is one of the first real-world studies to show the effectiveness of the tactic called doxyPEP, for doxycycline post-exposure prophylaxis, researchers said.

“Interventions that are effective in clinical trials don’t always end up working in real-world settings, where people tend to face more barriers to consistent medication use,” lead investigator Michael Traeger, a research fellow at Harvard Pilgrim Health Care Institute, said in a news release from the college.

“We were excited to see that doxyPEP users in our study experienced declines in chlamydia and syphilis comparable to those observed in clinical trials,” Traeger continued.

The study involved patients with Kaiser Permanente Northern California, a health system that began offering doxyPEP to gay and bisexual men in Nov. 2022 after San Francisco issued guidelines supporting the tactic.

Of nearly 12,000 people being treated for HIV, nearly one in five — more than 2,250 — received doxyPEP within its first year of availability, researchers found.

The team then looked at STI test results before and after doxyPEP became available, to see how the tactic might have affected risk.

They found a dramatic reduction in chlamydia and syphilis thanks to doxyPEP, and a slightly lower but significant reduction in gonorrhea infections.

Quarterly syphilis rates decreased from 1.7% prior to doxyPEP availability to 0.3% afterward, while quarterly chlamydia rates declined from 9.6% to 2%. Quarterly gonorrhea infections dropped from 10.2% to 9%.

At the same time, syphilis and chlamydia rates among those not prescribed doxyPEP remained stable, researchers noted.

“Since we started offering doxyPEP to our patients, our clinicians have seen a marked decline in both positive STI test results and the number of patients needing treatment after an STI exposure,” researcher Dr. Jonathan Volk, an infectious disease specialist with the Permanente Medical Group, said in a news release.

“But the reduction in gonorrhea in our study was modest, underscoring the importance of regular STI testing for patients using doxyPEP,” Volk added.

The approach isn’t without its concerns, including whether frequent use of doxycycline could lead to increased antibiotic resistance among STIs, researchers noted.

“In the meantime, our study suggests that broader implementation of doxyPEP could have tremendous benefits for reducing STI transmission and improving sexual health,” senior researcher Julia Marcus, an associate professor of population medicine at the Harvard Pilgrim Health Care Institute, concluded in the news release.

More information

The Centers for Disease Control and Prevention has more on doxyPEP.

SOURCE: Harvard Pilgrim Health Care Institute, news release, Jan. 6, 2025

Source: HealthDay