Doxycycline PEP for Prevention of Sexually Transmitted Infections Among Kenyan Women Using HIV PrEP

Inclusion Criteria: * Willing and able to give written informed consent * Age ≥18 years and ≤30 years old * Female sex at birth * HIV-seronegative at the time of last test within the past month and a current prescription for PrEP according to the national guidelines of Kenya (define PrEP eligibility as: partner of HIV-infected person not on ART or on ART for \<6 months, \>1 partner of unknown status, transactional sex, recent STI, recurrent HIV PEP use, inconsistent condom use, or injection drug use). Exclusion Criteria: * Pregnant * Breastfeeding a child * Allergy to tetracycline class * Current medications which may impact doxycycline metabolism or that are contraindicated with doxycycline, as per the prescribing information. These include systemic retinoids, barbiturates, carbamazepine, phenytoin, and warfarin. * Recent use of prolonged (more than 14 day course) antibiotics in the month prior to enrollment * Active, clinically significant medical or psychiatric conditions that would interfere with study participation, at the discretion of the site investigator or designee.