A Personalized, Transdiagnostic Smartphone App (Mello) Targeting Repetitive Negative Thinking for Depression and Anxiety: Qualitative Analysis of Young People’s Experience (Preprint)

BACKGROUND The increasing rates of mental health challenges among young people highlight an urgent need for accessible and effective treatment. However, current mental health systems face unprecedented demand, leaving most young people globally with unmet mental health needs. Smartphones present a promising solution to this issue by offering in-the-moment support through innovative just-in-time adaptive interventions, which provide support based on real-time data. OBJECTIVE This study explores young people’s experiences with Mello, a just-in-time adaptive intervention that focuses on the transdiagnostic mechanism of repetitive negative thinking (RNT), a significant factor contributing to youth depression and anxiety. METHODS Semistructured qualitative interviews were conducted with 15 participants aged 16 to 25 years, all of whom had previously participated in a pilot randomized controlled trial of Mello. Of the 15 participants, 9 (60%) identified as women, 4 (27%) as men (including 1 transgender man), and 2 (13%) as nonbinary. Interviews focused on participants’ experiences with the Mello app, factors influencing engagement, perceived benefits and limitations, and suggestions for future improvements. Thematic analysis was used to analyze the data. RESULTS The analysis identified three superordinate themes: Mello as a tool for intentional reflection; doing therapy your own way; and barriers to engagement during low mood, anxiety, and RNT. Theme 1 explored young people’s experiences of how the app facilitated active management of negative thoughts and supported the development of reflective habits, contrasting with their typical strategies of avoidance or resistance. Theme 2 highlighted the value of the app’s self-guided nature, with a particular focus on its flexibility and accessibility, particularly when compared to traditional face-to-face therapy. Finally, theme 3 addressed barriers to engagement, particularly during emotionally difficult times, with participants reporting feeling “stuck” in their negative thoughts. To mitigate these challenges, participants suggested incorporating gamification elements, such as progress-tracking visuals, to enhance motivation and increase engagement with the app. CONCLUSIONS Our findings underscored the value of Mello in promoting intentional engagement and reflection with RNT, consistent with prior research that emphasizes the effectiveness of tailored interventions. Although some users valued the self-guided nature of the application, others encountered difficulties with motivation. Future research should explore strategies to enhance engagement for young people with low mood and motivation, such as co-design methodologies, advanced personalization features, and gamification techniques.