Contribution of spontaneous improvement to placebo response in depression: A meta-analytic review

Abstract

ObjectivesIt is unknown to what degree spontaneous improvement accounts for the large placebo response observed in antidepressant trials for Major Depressive Disorder (MDD). The purpose of this study was to estimate the spontaneous improvement observed in treatment-seeking individuals with acute MDD by determining the symptom change in depressed patients assigned to wait-list controls in psychotherapy studies. MethodThe databases PubMed and PsycINFO were searched to identify randomized, prospective studies randomizing outpatients to psychotherapy or a wait-list control condition for the treatment of acute MDD. Standardized effect sizes calculated from each identified study were aggregated in a meta-analysis to obtain a summary statistic for the change in depression scores during participation in a wait-list control. ResultsTen trials enrolling 340 participants in wait-list control conditions were identified. The estimated effect size for the change in depression scores during wait-list control was 0.505 (95% CI 0.271–0.739, p < 0.001), representing an average improvement of 4 points on the Hamilton Rating Scale for Depression. DiscussionDepressed patients acutely experience improvement even without treatment, but spontaneous improvement is unlikely to account for the magnitude of placebo response typically observed in antidepressant trials. These findings must be interpreted in light of the small number wait-list control participants available for analysis as well as certain methodological heterogeneity in the psychotherapy studies analyzed.