When taken up to three days after having sex, the antibiotic doxycycline has been shown to prevent syphilis, gonorrhea and chlamydia in about two-thirds of users. 

Cases increased by nearly 80% to more than 207,000 between 2018 and 2022, according to the CDC. Rates increased among all age groups, including newborns, and in all regions of the country.

Doxy-PEP can be taken a few hours after sex and is effective at preventing sexually transmitted infections. New research finds it's less effective for women but that may not be the final word.