Robust, scalable strategies are essential for averting the development of mental health difficulties in adolescents and young adults. While digital mental health applications offer a promising route to widespread prevention, only a limited number have undergone high-quality, sufficiently powered randomized trials that draw on established frameworks of adaptive emotional development and incorporate individualized tailoring. This trial was designed to compare the effectiveness of a personalized emotional competence mobile application with a standard cognitive behavioral therapy (CBT) self-help application and a self-monitoring application in preventing the escalation of depressive symptoms among young people. The study used a multicentre, parallel-group, open-label randomized controlled design, nested within a broader cohort multiple randomized trial framework that also included a parallel evaluation of wellbeing promotion. It was implemented across four university-based trial centers located in the United Kingdom, Germany, Spain, and Belgium. Recruitment occurred through educational institutions and social media channels in each participating country. Eligible participants were individuals aged 16–22 years who displayed heightened vulnerability according to their baseline emotional competence assessment and who reported no history of major depressive disorder. Using an independent computerized randomization system with minimization for country, age, and self-reported gender, participants were assigned in a 1:1:1 ratio to usual care supplemented with either the personalized emotional competence self-help app, the generic CBT self-help app, or the self-monitoring app. Follow-up extended for 12 months after randomization. Assessors of outcomes remained blinded to treatment allocation. The primary endpoint consisted of depressive symptom severity, as assessed by the Patient Health Questionnaire-9 (PHQ-9), at the 3-month follow-up visit, with analysis restricted to those who provided data at that time point. The trial was prospectively registered on ClinicalTrials.gov (NCT04148508) and has now concluded. From Oct 15 2020, to Aug 3 2021, 1262 young people were recruited into the study: 417 were allocated to the emotional competence app, 423 to the CBT app, and 422 to the self-monitoring app. Participants had a mean age of 18.8 years (standard deviation 2.0). Of the 1262 individuals who reported their gender, 984 (78.0%) were female, 253 (20.0%) were male, 15 (1.2%) identified as neither, and 10 (0.8%) as both. Completion rates for the 3-month assessment were 178 participants in the emotional competence group, 191 in the CBT group, and 199 in the self-monitoring group. At this primary endpoint, the CBT app produced a statistically significant reduction in depressive symptoms relative to the self-monitoring app (mean difference on the PHQ-9: –1.18 [95% confidence interval –2.01 to –0.34]; P = 0.006). In contrast, symptom levels did not differ meaningfully between the emotional competence app and the CBT app (0.63 [–0.22 to 1.49]; P = 0.15), nor between the self-monitoring app and the emotional competence app (–0.54 [–1.39 to 0.31]; P = 0.21). Across all follow-up completers (n = 541), 31 individuals required hospital-based mental health care for reasons judged unrelated to the trial interventions (eight in the emotional competence app arm, 15 in the CBT arm, and eight in the self-monitoring arm). No fatalities occurred during the study period. Overall, the emotional competence app did not produce the anticipated improvements relative to the CBT app or self-monitoring condition. Nevertheless, for young people displaying heightened worry or rumination, negative thinking patterns, or elevated sensitivity to rejection, the CBT app helped slow progression of depressive symptoms. It supported better functioning and quality of life across the initial 3 months compared with the control condition. Benefits occurred amid modest engagement, leaving questions about long-term clinical significance. Mobile self-help applications built on proven CBT foundations may offer an accessible, economical, and expandable approach to promoting mental health among young people.
