Doxy As STI PEP FAQS Download Using doxycycline as STI PEP (post-exposure prophylaxis) is a new use for a well-known medication. Learn more about this new tool and how it's being used to prevent STIs! Please note that NCSD is not a medical clinic. Information here is intended as an overview, and shouldn't be used in place of advice from a licensed medical provider. Created by NCSD