The off-label use of doxycycline to prevent certain sexually transmitted infections (STIs), outside controlled research environments, has been occurring for several years. The objective of this study was to describe the off-label use of doxycycline as a preventive treatment for STIs by conducting a review of the literature, including analysis of a social network. In total, 11 eligible references were identified, comprising 9 letters and 2 original articles. One press article and six Reddit® discussions were also selected. Most doxycycline users identified in this study were men who have sex with men, with numerous partners and without using condoms. Doxycycline was mainly prescribed by a doctor, but some users obtain the medication in its veterinary form via the internet. HIV PrEP was identified as a factor leading to the decision to take doxycycline. While most users expressed confidence in its efficacy, some expressed reservations due to its inability to provide comprehensive protection against all STIs, and due to the occurrence of side effects. The increase in self-medication with doxycycline for STI prevention necessitates enhanced monitoring, addressing both disease transmission risks and potential adverse drug reactions.< Leer menos