STIs can be prevented with a single dose of doxycycline after sex

A study conducted in the United States has shown that a broad-spectrum antibiotic, doxycycline, is effective as a post-exposure prophylaxis for gonorrhoea, chlamydia and syphilis, amongst men who has sex with men (MSM) and transgender women. The results were published in the journal, News Medical. 

 554 people living with HIV, or taking pre-exposure prophylaxis (PrEP), took part in the study. Some participants received doxycycline (200mg within 3 days of condomless sex) and a control group received nothing.

The results of the study showed that participants who received doxycycline had significantly fewer sexually transmitted infections than those who did not receive the drug. The results were comparable for those living with HIV and those taking PrEP. Doxycycline was reported to be generally safe and well tolerated.

“At this point, doxycycline after sex is a targeted intervention for certain populations, in this case men who have sex with men or transgender women who have already had an STI in the past year." Dr. Annie Luetkemeyer, professor of infectious diseases, University of California San Francisco

The study is yet to establish whether the use of doxycycline in this manner could lead to increased antibiotic resistance or lead to harm to gut bacteria.