Abstract
Opp is a universal mental health-promoting mobile application (app) developed for adolescents, with the aim of promoting mental health and well-being and preventing mental health problems. In this randomized controlled trial, the effectiveness of Opp was tested among Norwegian adolescents aged 13 to 25 years. Mental health, well-being, self-efficacy, self-esteem, help-seeking behavior, and sleep quality were assessed at two measurement points (T1 and T2), that were approximately 11 weeks apart. Only the participants that answered at both measurement points were included in the main analyses (N = 399; 75 % girls; Mage = 16.90 years, SD = 1.40). The results demonstrated a statistically significant effect of the app on mental health, as measured by the SDQ Total Difficulties scale (F(1,790) = 4.35, p = .037), while no statistically significant effects were observed on the other outcomes. These results provide important insights, and a broader understanding of how mental health apps can influence the mental health and well-being of a general sample of adolescents.