Effects and side effects of a transdiagnostic bias modification intervention in a mixed sample with obsessive-compulsive and/or depressive symptoms-a randomized controlled trial.

Obsessive-compulsive disorder (OCD) and major depression disorder (MDD) are underdiagnosed and undertreated mental disorders. Prior studies have verified the efficacy of the self-help manual My Metacognitive Training (myMCT) for patients with primary OCD. As depression and OCD share a number of (meta)cognitive biases and dysfunctional coping strategies, we examined the efficacy of myMCT in a mixed patient sample with OCD and/or depression. A total of 80 Italian-speaking individuals with symptoms of OCD and/or depression were randomized to either myMCT or to a waitlist control group (both groups had access to care as usual during the intervention). Post-assessment was carried out 6 weeks after inclusion. Scores on the Beck Depression Inventory-II scale (BDI-II) served as the primary outcome. Adverse effects were assessed with a newly devised self-report scale. Participants in the myMCT condition showed significant symptom improvement on the BDI-II scale at a medium to large effect size compared to the control group (using intention-to-treat and per protocol analyses). The intention-to-treat analyses yielded significant positive effects on the PHQ-9 scores and psychological as well as environmental well-being in favor of myMCT; for the OCI-R total score, group differences bordered significance in favor of the myMCT. The most prevalent adverse effects were feeling pressured by the suggested exercises or feeling bad due to not performing the exercises correctly. Our results indicate that the myMCT manual represents an effective program for patients with OCD as well as those with depressive symptoms in an Italian-speaking population. Adverse events due to unguided self-help deserve more attention in the future.