This article aims to assess the prevalence and factors associated with self-medication in adolescents. Cross-sectional study, nested in cohort, with 2,515 adolescents aged 18-19 years born in São Luís-MA. The use of medication in the last 15 days without a medical prescription or by a qualified professional was considered self-medication. Factors associated with self-medication were evaluated using Poisson regression with robust variances and hierarchical selection of variables. Medicines were used in the last 15 days by 48.05% of adolescents. Among these, 70.09% use it without a prescription or indication from another health professional. The most used medications for self-medication were "over the counter" (93.68%). Self-medication was positively associated with female gender (PR: 1.41; 95%CI: 1.25-1.59), screen time ≥5h/day (PR: 1.32; 95%CI: 1.05-1.67) and self-reported diagnosis of allergic rhinitis (PR: 1.19; 95%CI: 1.02-1.39); however, negatively associated with self-satisfaction with health (PR: 0.79; 95%CI: 0.67-0.94) and hospitalization in the previous year (PR: 0.70; 95%CI: 0.50-0.97). Self-medication was common among adolescents and to reduce this practice, greater attention should be given to women, individuals with intense exposure to meshes and allergic diseases.