Concentrated Exposure Therapy vs Internet-Based Cognitive Behavioral Therapy for Obsessive-Compulsive Disorder

Importance Given the high prevalence, chronicity, and associated disability of obsessive-compulsive disorder (OCD), optimizing treatment is a global priority. The Bergen 4-day treatment (B4DT), a concentrated exposure-based intervention, may reduce treatment burden and improve access to evidence-based care. Objective To evaluate the efficacy of B4DT compared with internet-based cognitive behavioral therapy (iCBT) in reducing OCD symptom severity. Design, Setting, and Participants Single-center randomized controlled trial (1:1 allocation). Between May 8, 2024, and August 8, 2025, adults (aged 18 to 72 years) with OCD were enrolled and were followed up for 3 months. Key exclusion criteria included schizophrenia, bipolar disorder, acute suicidality, substance dependence, and recent psychopharmacological changes. Outcomes were assessed at baseline, 6 weeks, 8 weeks (posttreatment), and 3 months (follow-up) by masked evaluators. Interventions Patients were randomized to B4DT (including preparatory sessions) or an 8-week unguided iCBT program. Main Outcomes and Measures The primary outcome was the change in OCD symptom severity, measured by the Yale-Brown Obsessive Compulsive Scale (Y-BOCS). Secondary outcomes included self-reported OCD (OCI-R), dysfunctional cognitions, quality of life, depressive symptoms, experiential avoidance, global functioning, self-esteem, and treatment satisfaction. Results A total of 253 individuals were screened, and 119 were enrolled after 53 were found to be ineligible and 81 declined to participate. Sixty of the 119 randomized participants (mean [SD] age, 33.5 [10.1] years; 79 [66.4%] women) were assigned to B4DT and 59 to iCBT. The primary analysis included all randomized participants (intention-to-treat). B4DT was associated with significantly greater reductions in OCD symptoms (Y-BOCS) than iCBT, with large effects at posttreatment (mean [SE] difference, −7.9 [0.9]; 95% CI, −9.7 to −6.0; Hedges g , −1.6) and sustained effects at 3-month follow-up (mean [SE] difference, −5.6 [1.1]; 95% CI, −7.8 to −3.4; Hedges g , −1.0). Secondary outcomes consistently favored B4DT. Response and remission rates at 3-month follow-up were higher with B4DT (35 of 57 [61.4%] vs 11 of 44 [25.0%] and 24 of 57 [42.1%] vs 6 of 44 [13.6%], respectively). Conclusions and Relevance In this randomized clinical trial of 119 adults with OCD, B4DT was superior to iCBT in reducing OCD symptom severity, with sustained benefits. Its brief, concentrated format may represent a scalable strategy to improve access to effective OCD treatment globally.