Placebo Effect in Randomized Trials of Major Depressive Disorder With Psychotic Features: A Systematic Review and Descriptive Meta-Analysis

Abstract

Background: In the 1980s, the response rate of major depressive disorder with psychotic features (MDD-Psy) to placebo pills was reported to be close to 0%. To our knowledge, this placebo response rate has not been systematically reassessed. We undertook a systematic review of randomized controlled trials (RCTs) that have used a placebo or sham control group for MDD-Psy.

Methods: We searched MEDLINE and identified 9 relevant publications reporting on 10 studies comparing a placebo or sham interventions versus an active intervention. We extracted reported rates of response or of dropout for all causes associated with placebo versus active intervention(s) and aggregated response and dropout rates across trials.

Results: Two sham-controlled electroconvulsive therapy (ECT) trials did not provide response rates. In the 3 pharmacotherapy studies published in the 1980s, 0 of 12 participants (0%) responded to placebo versus 13 of 38 (34.2%) responding to the active interventions. In contrast, 5 RCTs published in the 2000s, 114 of 339 participants (33.6%) randomized to placebo responded versus 149 of 373 participants (39.9%) randomized to active interventions; dropout rates were 71/236 (30.1%) for placebo versus 84/282 (29.8%) for the active interventions.

Conclusions: As expected, response rates to placebo pills in RCTs for MDD-Psy increased markedly from the 1980s to the 2000s. Methodological issues in the design and conduct of more recent RCTs may have contributed to the high placebo response. However, one needs to consider this placebo response rate when interpreting the result of recent trials of MDD-Psy, which typically have not included a "pure" placebo condition.