The Affective Pathway to Cognitive Change: How Depressive Symptoms Mediate Metacognitive Improvement in <scp>OCD</scp> Treatment

ABSTRACT Background Although metacognitive beliefs are recognised as central to obsessive compulsive disorder (OCD), the mechanisms by which cognitive behavioural therapy (CBT) targets these beliefs remain under‐investigated. Specifically, the affective pathways linking symptom reduction to metacognitive change are poorly understood. Methods This study had two primary objectives: (1) to examine the longitudinal effects of CBT on metacognitive beliefs in individuals with OCD and (2) to explore whether the relationship between symptom reduction and metacognitive improvement is mediated by changes in depression or trait anxiety. A clinical sample of individuals with OCD ( n = 60) and a matched healthy control group ( n = 60) were assessed. Patients in the OCD group underwent a 10‐session manualised CBT protocol. Measures of OCD symptoms (Y‐BOCS), depression (BDI), trait anxiety (STAI‐T) and metacognitions (MCQ‐30) were administered at pre‐treatment, post‐treatment and 6‐month follow‐up. Results Linear mixed‐effects models confirmed that CBT was highly effective, producing significant longitudinal reductions in OCD symptoms, depression, anxiety and dysfunctional metacognitions. Longitudinal mediation analysis revealed that the reduction in OCD symptoms led to an improvement in metacognitive beliefs (specifically uncontrollability/danger and need to control thoughts) through the alleviation of depressive symptoms. In contrast, changes in trait anxiety did not mediate this relationship. Conclusions These findings suggest that while standard CBT effectively reduces both symptoms and dysfunctional beliefs, the mechanism of cognitive change is specifically driven by the alleviation of the depressive burden of OCD rather than a general reduction in anxiety. This highlights the importance of targeting depressive affect to facilitate deeper metacognitive change and sustain long‐term treatment gains.