Currently, after-sex antibiotics are not used for preventing bacterial sexually-transmitted infections (STIs), but research has been encouraging, at least for syphilis and chlamydia.

The study was presented at the 2017 Conference on Retroviruses and Opportunistic Infections. It involved 232 MSM who were participants in an HIV-prevention trial.

Half of the men were instructed to take an antibiotic called doxycycline within 72 hours of condomless sex. The other half were not given any antibiotics. All of the men were advised on safe sex practices and provided with condoms.

Over the next several months, the men were tested for syphilis, gonorrhea, chlamydia, and HIV every eight weeks.

Overall, almost a quarter of the men in the doxycycline group developed an STI. The rate was 39% for the men who took no antibiotics. Seventy-one percent of the STIs did not have any symptoms.

Rates of syphilis and chlamydia were lower for the men who took doxycycline. But gonorrhea rates were about the same for the two groups.

The researchers concluded that STI risk decreased by 47% for men in the doxycycline group.

While these results are encouraging, there is more research to be done. Experts are still not sure how well this method would work for the long term or whether antibiotic resistance would be a problem.

Not all STIs are caused by bacteria. Other infections, like herpes, hepatitis, HIV, and human papillomavirus (HPV) are viral infections and would not be respond to antibiotics.

To reduce your risk for STIs, consider the following steps:

• Always use a condom during all sexual encounters, including vaginal, oral, and anal sex. Talk to your partner about safe sex practices. 

• Make sure you know your infection status. Get tested regularly. Keep in mind that you can have an STI even if you don’t have any symptoms.

• Be sure that your partner is infection-free.

• If you think you or your partner might have an STI, stop having sex and see a doctor as soon as possible. Don’t resume sexual activity until you are positive the infection is gone.