Mindfulness and Mentalization Smartphone-Based Ecological Momentary Interventions for Common Mental Health Problems: A Pilot Randomized Controlled Trial

Background: Accessible Ecological Momentary Interventions deliver brief, real-time support integrated into daily routines. Interpersonal dynamics and maladaptive coping mechanisms, can contribute to an individual's anxiety and depression. Both mindfulness and mentalization represent psychological constructs with the potential to mitigate the negative impact of interpersonal stressors.Objective: To assess the feasibility and acceptability of an automated mindfulness and mentalization-based ecological momentary intervention for common mental health problems as delivered via a mobile phone app.Design: Parallel-group pilot randomised controlled trial with 1:1 allocation ratio and exploratory framework.Methods: Participants experiencing common mental health problems were recruited online, from a University setting. Eligible participants were randomly allocated to fully automated mindfulness-based or mentalization-based ecological momentary interventions via computer-generated randomisation. Participants were blind to the alternative intervention options. Outcomes were self-assessed through questionnaires after four weeks. Primary outcomes were feasibility (recruitment, retention, adherence) and acceptability (satisfaction ratings, qualitative feedback). Secondary outcomes included changes in depression (PHQ-9) and anxiety (GAD-7) scores.Results: Eighty-four participants were randomised (42 to each group). The interventions demonstrated good feasibility with 89.2% retention rate and mean adherence of 87.69% across both groups. Acceptability ratings were positive, with favourable scores for ease of engagement (M = 5.20), overall enjoyment (M = 5.15), and likelihood of recommending the app (M = 5.11) on a 7-point scale. For primary outcomes, both groups showed significant within-group reductions in PHQ-9 and GAD-7 scores, with moderate to large effect sizes ( d= -0.68 to -0.81), with no significant difference between groups. Both treatments demonstratedclinically significant effectiveness in reducing symptoms below diagnostic thresholds (42 - 46%). Mindfulness performed better on improving assertiveness and perceived support compared to mentalization in the momentary EMA data. One unintended harm was reported in the mindfulness arm, none in the mentalization arm.Conclusions: This pilot trial suggests that both mindfulness and mentalization-based ecological momentary interventions are feasible and acceptable for individuals with common mental health problems and warrant further evaluation.