Demographic Variables, Design Characteristics, and Effect Sizes of Randomized, Placebo-Controlled, Monotherapy Trials of Major Depressive Disorder and Bipolar Depression

Objective: The aim of this work is to compare the efficacy of pharmacologic agents for the treatment of major depressive disorder (MDD) and bipolar depression.

Data Sources: MEDLINE/PubMed databases were searched for studies published in English between January 1980 and September 2014 by cross-referencing the search term placebo with each of the antidepressant agents identified and with bipolar. The search was supplemented by manual bibliography review.

Study Selection: We selected double-blind, randomized, placebo-controlled trials of antidepressant monotherapies for the treatment of MDD and of oral drug monotherapies for the treatment of bipolar depression. 196 trials in MDD and 19 trials in bipolar depression were found eligible for inclusion in our analysis.

Data Extraction: Data were extracted by one of the authors and checked for accuracy by a second one. Data extracted included year of publication, number of patients randomized, probability of receiving placebo, duration of the trial, baseline symptom severity, dosing schedule, study completion rates, and clinical response rates.

Results: Response rates for drug versus placebo in trials of MDD and bipolar depression were 52.7% versus 37.5% and 54.7% versus 40.5%, respectively. The random-effects meta-analysis indicated that drug therapy was more effective than placebo in both MDD (risk ratio for response = 1.373; P < .001) and bipolar depression (risk ratio = 1.257; P < .001) trials. The meta-regression analysis suggested a statistically significant difference in the risk ratio of responding to drug versus placebo between MDD and bipolar depression trials in favor of MDD (P = .008).

Conclusions: Although a statistically significantly greater treatment effect size was noted in MDD relative to bipolar depression studies, the absolute magnitude of the difference was numerically small. Therefore, the present study suggests no clinically significant differences in the overall short-term efficacy of pharmacologic monotherapies for MDD and bipolar depression.