The Modulatory Role of Communicated Treatment Rationale on Treatment Expectation Effects in Depression.

Placebo groups in clinical trials on depression show impressive improvements. Yet, there is little research on the mechanism underlying this effect. The aim of this study is to assess how patients' treatment expectations modulate the placebo treatment effects. We expect that patients' treatment expectation determines placebo responses and treatment outcomes, and that this expectation is influenced by the disorder explanations (information about the illness models) typically provided during the initial medical encounters that precede treatment. In the study we aim to manipulate depressed patients' expectations by providing two different clinician-delivered illness and treatment rationales (biological/ psychological). Patients will then receive placebo treatment (pharmacological/ psychological), that is either congruent or incongruent with the previously communicated treatment rationale. Hypotheses: 1. Providing a treatment-congruent treatment rationale leads to a better outcome than providing treatment-incongruent rationales. 2. Treatment-congruent explanations reduce the risk of side effect development, in particular in the medication arm. 3. Inter-individual differences in the effect of provided treatment rationale are associated with pre-treatment experiences and expectations, depression severity and comorbid anxiety.