Supplementary Material for: Group Acceptance and Commitment Therapy versus Cognitive Behavioral Therapy/Exposure Response Prevention for Obsessive Compulsive Disorder: A Block Randomized Controlled Trial

Introduction: Acceptance and Commitment Therapy (ACT) may be as effective for treating Obsessive Compulsive Disorder (OCD) as the gold standard treatment, Cognitive Behavioral Therapy (CBT) with Exposure Response Prevention (ERP), but ACT has never been directly compared to CBT/ERP in a randomized control trial. Objective: This study aimed to compare the efficacy of group-based ACT and CBT/ERP in two outpatient mental health service clinics for adults with OCD. Methods: A total of 176 patients with OCD participated in a single-blinded, non-inferiority, block randomized controlled trial. Patients were assigned to either the ACT (n = 101) or CBT/ERP (n = 75) groups for 14 weekly sessions. The primary outcome was the Yale-Brown Obsessive Compulsive Scale (Y-BOCS) score at post-treatment and at the 6-months follow-up with pre-specified non-inferiority criteria. Quality of life, measured using the Quality of Life Inventory (QOLI), was the secondary outcome. Results: Linear mixed models showed that Y-BOCS scores in the ACT group were non-inferior to those in the CBT/ERP group both post-treatment and at 6, and 12-months of follow-up. QOLI scores also showed no significant differences in ACT compared to CBT/ERP across the three measurement points. Conclusions: This randomized controlled trial demonstrated that group-delivered ACT is non-inferior to CBT/ERP in reducing OCD symptoms and improving the quality of life of patients with OCD in outpatient mental health services. These findings suggest that ACT may serve as a viable alternative to CBT/ERP in adults with OCD in outpatient mental health settings, although further replication is necessary.