David L. Dawson

Objectives The present demand for child and adolescent mental health services exceeds the capacity for service provision. Greater research is required to understand the utility of accessible self‐help interventions, such as mobile apps. This study sought to investigate whether use of a mental health app, underpinned by CBT, led to changes in psychological distress amongst adolescents. Mechanisms of change were examined, specifically whether changes are attributable to cognitive strategies. Design This study utilised a multiple‐baseline single‐case experimental design, tracking variables across baseline and intervention phases. Surveys assessing participant experience were also administered. Methods Five participants with moderate‐to‐severe levels of psychological distress engaged with a CBT‐based app over five weeks. Participants were recruited from both a well‐being service and the general population. Supplementary weekly calls to participants offered clarification of app content. Results A small overall effect of the intervention of psychological distress was evident; however, outcomes were dependent on the analysis conducted. The intervention appeared to promote an increase in use of adaptive cognitive strategies but not negative thinking styles. The CBT app did not promote changes in participant well‐being. Participant feedback highlighted practical challenges of utilising the app. Conclusions The clinical benefits of app‐based CBT were small, and a range of barriers to engagement were recognised. While further research is required, caution should be exercised in the interpretation of studies reporting on app effectiveness.