The risk for comorbid major depressive disorder and obesity is increased in adolescents and adults with attention-deficit/ hyperactivity disorder (ADHD), and adolescent ADHD predicts adults major depressive disorder and obesity. Nonpharmacological interventions to prevent these comorbidities are urgently needed. Bright light therapy (BLT) improves day-night rhythm and is an established therapy for major depression in adolescents and adults. Exercise prevents and reduces obesity in adolescents and adults and also improves depressive symptoms. Interestingly, a reinforcement-based intervention using a mobile health app (m-Health) resulted in improved effects on weightloss in obesity. The aim of the current pilot randomized-controlled phase-IIa study is to establish feasibility and effect sizes of two kinds of interventions, BLT and exercise, in combination with m-Health based monitoring and reinforcement in adolescents and young adults aged 14 to 29 years old with ADHD, targeting the prevention of depressive symptoms and obesity. In addition, immediate and long-term treatment effects on ADHD specific psychopathology, health related quality of life, fitness and body related measures, neurocognitive functions and chronotype are explored. Furthermore, saliva samples are taken in a subgroup of adult patients to explore the effects of BLT and exercise on concentrations of hormones. This subgroup of adult patients will also participate in an additional neuroimaging study of the reward system in order to explore intervention effects on striatal reward reactivity.