The Bergen 4-day treatment for OCD: A systematic review

The Bergen 4-day treatment (B4DT) for obsessive-compulsive disorder (OCD) is a concentrated, exposure-based intervention delivered in a group format. Research into the B4DT has proliferated in the last decade. However, there has been no systematic review of the literature on the B4DT to date. This systematic review aimed to evaluate the effectiveness, long-term outcomes, acceptability, and factors affecting outcomes of the B4DT for OCD. Any peer-reviewed study published in English between 2012 and February 2026 which evaluated the B4DT for OCD in at least one of these domains was eligible for inclusion. A search of PubMed, PsycInfo, Scopus, Embase, the Cochrane Library, ProQuest Dissertations and Theses, and EBSCO Open Dissertations was conducted in March 2026. Owing to a lack of randomised controlled trials (RCTs), results were synthesised in a narrative review. Thirty-eight eligible studies were identified, including 27 studies with original data. Combining all intervention studies using original data yielded a total sample of 1144 B4DT participants. Only one RCT of the B4DT was identified. All intervention studies included in the review found the B4DT to be an effective treatment for OCD. There is also evidence to suggest that treatment gains are maintained long-term. Satisfaction ratings of the treatment were high, while attrition rates were low. Various predictors of treatment outcomes were identified. However, the overall quality of the evidence pertaining to the B4DT was poor, since almost all studies lacked comparators. Future research should evaluate the B4DT against current first-line treatments for OCD using RCTs.