Background: This study is a randomized, prospective, investigation of the relationships between clinical trial design, patient expectancy and the outcome of treatment with antidepressant medication. Method Adult out-patients with major depressive disorder (MDD) were randomized to either placebo-controlled (PC, 50% probability of receiving active medication) or comparator (COMP, 100% probability of receiving active medication) administration of antidepressant medication. Independent-samples t tests and analysis of covariance (ANCOVA) were used to determine whether the probability of receiving active medication influenced patient expectancy and to compare medication response in the PC v. COMP conditions. We also tested the correlations between baseline expectancy score and final improvement in depressive symptoms across study groups.
Results: Subjects randomized to the COMP condition reported greater expectancy of improvement compared to subjects in the PC condition (t = 2.60, df = 27, p = 0.015). There were no statistically significant differences in the analyses comparing antidepressant outcomes between subjects receiving medication in the COMP condition and those receiving medication in the PC condition. Higher baseline expectancy of improvement was correlated with lower final depression severity scores (r = 0.53, p = 0.021) and greater improvement in depressive symptoms over the course of the study (r = 0.44, p = 0.058).
Conclusions: The methods described represent a promising way of subjecting patient expectancy to scientific study. Expectancy of improvement is affected by the probability of receiving active antidepressant medication and seems to influence antidepressant response.