BACKGROUND: The COVID-19 pandemic has been suggested to constitute a broad base stressor with severe mental health consequences. mHealth applications are accessible self-help tools that can be used to reduce psychological distress during the pandemic. This randomized controlled trial evaluated the effects of mobile-based cognitive training exercises on COVID-19 related distress and maladaptive cognitions. METHODS: Following initial screening (n = 924), participants scoring 1 standard deviations above the mean of the COVID-19 Distress Scale were randomized into two groups. Participants in the immediate-app group (iApp; n = 25) started using the application at baseline (T0) for 12 days (from T0 to T1). Participants in the delayed-app group (dApp; n = 22) started using the mobile application at T1 (crossover) and used it for the following 12 days (T1 to T2). RESULTS: Intention to treat analyses indicated that the iApp group exhibited lower COVID-19 distress, lower depression, fewer intolerance of uncertainty and obsessive beliefs than the dApp group at T1. In addition, using the app for 12 consecutive days was associated with large effect-size reductions (Cohen's d ranging from 0.81 to 2.35) in COVID-19 distress and related maladaptive cognitions in the iApp group (from T0 to T1) and the dApp group (from T1 to T2). Moreover, these reductions were maintained at the follow-up. LIMITATIONS: This study was a crossover trial with a relatively limited sample size and mainly female participants. CONCLUSION: Our findings underscore the usefulness of brief, low-intensity, portable interventions in alleviating the negative effects of the pandemic on mental health.
