Mechanisms of change and heterogeneous treatment effects in psychodynamic and cognitive behavioural therapy for patients with depressive disorder: a randomized controlled trial

Background Major depressive disorder (MDD) is a prevalent psychiatric condition associated with significant disability, mortality and economic burden. Cognitive behavioral therapy (CBT) and psychodynamic psychotherapy (PDT) are found to be equally effective for patients with depression. However, many patients do not respond sufficiently to either treatment. To offer individualized treatment, we need to know if some patients benefit more from one of the two therapies. At present little is known about what patient characteristics (moderators) may be associated with differential outcomes of CBT and PDT, and through what therapeutic processes and mechanisms (mediators) improvements occur in each therapy mode. Presently only theoretical assumptions, sparsely supported by research findings, describe what potentially moderates and mediates the treatment effects of CBT and PDT. The overall aim of this study is to examine theoretically derived putative moderators and mediators in CBT and PDT and strengthen the evidence base about for whom and how these treatments works in a representative sample of patients with MDD. Methods One hundred patients with a diagnosis of MDD will be randomized to either CBT or PDT. Patients will be treated over 28 weeks with either CBT (one weekly session over 16 weeks and three monthly booster sessions) or PDT (one weekly session over 28 weeks). The patients will be evaluated at baseline, during the course of therapy, at the end of therapy, and at follow-up investigations 1 and 3 years post treatment. A large range of patient and observer rated questionnaires (specific preselected putative moderators and mediators) are included. Discussion The clinical outcome of this study may better guide clinicians when deciding what kind of treatment any individual patient should be offered. Moreover, the study aims to further our knowledge of what mechanisms lead to symptom improvement and increased psychosocial functioning. Trial registration ClinicalTrials.gov Identifier: NCT03022071