The Importance of Symptom Reduction for Functional Improvement after Cognitive Behavioral Therapy for Anxiety and Depression: A Causal Mediation Analysis

Introduction: The temporal relationship between symptoms and functioning in the context of cognitive behavioral therapy (CBT) for anxiety and depression is not fully understood, and there are few high-quality studies that have examined to what extent late intervention effects of CBT on functioning are mediated by initial intervention effects on symptoms while accounting for the initial effects on functioning and vice versa. Objective: The aim of the study was to investigate whether intervention effects on symptoms and functioning at 12-month follow-up were mediated by intervention effects on these outcomes at 6-month follow-up. Methods: Participants with anxiety and/or mild-to-moderate depression were randomly assigned to a primary mental health care service (n = 463) or treatment-as-usual (n = 215). Main outcomes were depressive symptoms (Patient Health Questionnaire [PHQ-9]), anxiety (General Anxiety Disorder-7 [GAD-7]), and functioning (Work and Social Adjustment Scale [WSAS]). Direct/indirect effects were derived using the potential outcomes and counterfactual framework. Results: The intervention effect on functioning at 12 months was largely explained by intervention effects at 6 months on depressive symptoms (51%) and functioning (39%). The intervention effect on depressive symptoms at 12 months was largely explained by the intervention effect at 6 months on depressive symptoms (70%) but not by functioning at 6 months. The intervention effect on anxiety at 12 months was only partly accounted for by intervention effects at 6 months on anxiety (29%) and functioning (10%). Conclusions: The findings suggest that late intervention effects of CBT on functioning were to a substantial degree explained by initial intervention effects on depressive symptoms even after accounting for initial effects on functioning. Our results support the importance of symptoms as an outcome in the context of CBT delivered in primary health care.