One dose of DoxyPEP can prevent STIs

Many people experience no side effects when taking doxycycline, though it may cause mild gastrointestinal side effects (e.g., throat pain, stomach upset, or diarrhea) and can increase sun sensitivity. If you take DoxyPEP frequently, it's especially important to protect your skin from the sun when spending time outdoors.

Some people should avoid DoxyPEP, including those who take doxycycline for another health condition (e.g. acne), those who are pregnant, and those who are allergic to doxycycline.

Beyond short-term side effects, there are bigger-picture questions about whether DoxyPEP might contribute to antibiotic resistance, making STIs more difficult to treat in the future. More long-term research is needed to understand how significant this concern might be.