Depressive symptoms are common, yet only a subgroup of individuals receive adequate treatment. To reduce the treatment gap, several online self-help programs have been developed, yielding small to moderate effects. We developed a smartphone self-help application addressing depressive symptoms. We sought to evaluate its feasibility and efficacy in participants reporting a subjective need for help (a diagnosis of depression was not mandatory). We conducted a randomized controlled trial (N = 90). The primary outcome was a reduction of depressive symptoms measured with the Patient Health Questionnaire-9 (PHQ-9). Secondary outcomes included improved self-esteem (Rosenberg Self-Esteem Scale) and quality of life (WHOQOL-BREF). The intervention group obtained access to the application for four weeks, the wait-list group received access after the post assessment. No group differences emerged in either outcome in intention-to-treat analyses. Per protocol analyses with frequent users (i.e., several times a week or more) yielded a small effect size (η2p = 0.049) at trend level on the reduction of depressive symptoms in favor of the treatment group. However, 39% of the participants did not use the application frequently. Mobile self-help applications represent a promising addition to existing treatments, but it is important to increase patients' motivation to use them.
