The CCT-D Trial: Evaluating the efficacy of the app-based cognitive control training de:)press ® as an add-on to standard inpatient care for depression – Study protocol for a randomized controlled trial

Background Depression is one of the most common and disabling mental health conditions. Despite evidence-based treatments, fewer than half of affected individuals achieve full remission. This may be due to limited targeting of cognitive vulnerabilities such as impaired control and negative information processing. Cognitive control training offers a promising add-on, with the adaptive Paced Auditory Serial Addition Task designed to activate prefrontal areas and promote neuroplasticity. Digital interventions, especially mobile apps, are increasingly recommended as adjuncts to standard care. This trial tests whether cognitive control training via the app de:)press® added to inpatient care reduces depressive symptoms more effectively and sustainably than a control condition in specialized wards for affective disorders. Methods This randomized, placebo-controlled trial will be conducted at two inpatient centers. A total of 106 adults diagnosed with unipolar depression will be randomly assigned to receive either standard inpatient care alone or standard care plus de:)press® . The app will be provided for six weeks. The primary outcome is clinician-rated symptom severity, measured four weeks after the intervention using the Hamilton Depression Rating Scale. Secondary outcomes include self-rated symptoms, well-being, neuropsychological functioning, and both trait and state rumination. Treatment expectations will be examined in relation to motivation, satisfaction, and outcome. Potential moderators such as age, gender, medication, cognitive style, and illness characteristics will also be analyzed. Discussion This trial examines whether app-based cognitive training can enhance treatment outcomes in inpatient depression care. If effective, it may offer a scalable, low-threshold tool to support recovery. Trial registration : German Clinical Trials Register: DRKS00037075 on 03 June 2025, last updated on 28 July 2025, https://www.drks.de/search/de/trial/DRKS00037075.