Treatment outcomes across OCD symptom dimensions in internet-delivered cognitive behaviour therapy: A routine care evaluation

Clinical presentations of obsessive-compulsive disorder are heterogeneous. While Internet-based cognitive behaviour therapy (iCBT) is an efficacious treatment for OCD symptoms as a whole, it is unclear if iCBT is effective across different OCD symptom profiles. This study evaluated iCBT outcomes across four common OCD symptom dimensions in 2136 adults undertaking treatment in routine care. At pre-, mid- and post-treatment, participants completed a measure of OCD symptom dimensions, as well as measures of depression, psychological distress, and disability. The most common primary OCD symptom dimensions were unacceptable thoughts (reported by 660 participants, 30.9% of the sample) and responsibility for harm (n = 461, 21.6%). Primary contamination (n = 388, 18.2%) and symmetry symptoms (n = 270, 12.6%) were less common, as were multiple primary OCD dimensions (n = 357, 16.7%). iCBT was consistently associated with large effect size reductions in individuals' most severe presenting OCD symptoms regardless of the type of symptom dimension (gs = 1.45-1.62). iCBT was also associated with significant reductions in overall OCD symptoms (g = .99), depression (g = .70), distress (g = .90) and disability (g = .44). Findings suggest that common OCD symptom dimensions are responsive to standard iCBT and that iCBT should continue to be recommended and prescribed in routine clinical care settings.