Universal school-based mental health programs for adolescents intend to promote wellbeing, but some evidence suggest that they may also cause harm. This scoping review aimed to map the state of knowledge on potential harms associated with these programs from the recent literature. Following the Preferred Reporting Items for Systematic reviews and Meta-Analyses extension for Scoping Reviews guidelines, four databases were searched for peer-reviewed studies published between 2019 and 2024. Articles were included if they evaluated a universal school-based mental health program for adolescents (13-18 years) and reported at least one quantitative outcome measure. Potential harms identified were classified into five harm types based on the observed data. Results showed that, of the 58 included studies, 29% (17 of 58) reported at least one type of potential harm. Statistically significant change in the overall sample was examined in all studies, with 16% (nine of 58) showing deterioration in at least one outcome. Statistically significant change by subgroup (e.g., age, gender, and baseline mental health) was examined in 21 studies, with 29% (six of 21) of these showing deterioration in at least one subgroup. Additional harms were identified through clinically meaningful deterioration, qualitative participant feedback, and safety protocols. Our findings confirm that universal school-based mental health programs can be associated with potential harms. Implications for research and practice are discussed.