Placebo response of non-pharmacological and pharmacological trials in major depression: a systematic review and meta-analysis

André Russowsky Brunoni, Mariana Lopes, Ted J Kaptchuk, Felipe Fregni, André Russowsky Brunoni, Mariana Lopes, Ted J Kaptchuk, Felipe Fregni

Abstract

Background: Although meta-analyses have shown that placebo responses are large in Major Depressive Disorder (MDD) trials; the placebo response of devices such as repetitive transcranial magnetic stimulation (rTMS) has not been systematically assessed. We proposed to assess placebo responses in two categories of MDD trials: pharmacological (antidepressant drugs) and non-pharmacological (device- rTMS) trials.

Methodology/principal findings: We performed a systematic review and meta-analysis of the literature from April 2002 to April 2008, searching MEDLINE, Cochrane, Scielo and CRISP electronic databases and reference lists from retrieved studies and conference abstracts. We used the keywords placebo and depression and escitalopram for pharmacological studies; and transcranial magnetic stimulation and depression and sham for non-pharmacological studies. All randomized, double-blinded, placebo-controlled, parallel articles on major depressive disorder were included. Forty-one studies met our inclusion criteria - 29 in the rTMS arm and 12 in the escitalopram arm. We extracted the mean and standard values of depression scores in the placebo group of each study. Then, we calculated the pooled effect size for escitalopram and rTMS arm separately, using Cohen's d as the measure of effect size. We found that placebo response are large for both escitalopram (Cohen's d - random-effects model - 1.48; 95%C.I. 1.26 to 1.6) and rTMS studies (0.82; 95%C.I. 0.63 to 1). Exploratory analyses show that sham response is associated with refractoriness and with the use of rTMS as an add-on therapy, but not with age, gender and sham method utilized.

Conclusions/significance: We confirmed that placebo response in MDD is large regardless of the intervention and is associated with depression refractoriness and treatment combination (add-on rTMS studies). The magnitude of the placebo response seems to be related with study population and study design rather than the intervention itself.

Conflict of interest statement

Competing Interests: The authors have declared that no competing interests exist.

Figures

Figure 1. QUOROM flow chart used to…
Figure 1. QUOROM flow chart used to identify studies for detailed analysis.
Figure 2. Forest plots showing placebo response…
Figure 2. Forest plots showing placebo response in control groups of escitalopram (A) and rTMS (B) studies.
Forest plots show effect sizes from the random effects model. A negative effect indicates that endpoint depression scores in control groups are higher than baseline scores. Effect sizes are Cohen's d (standardized mean difference), error bars represent the 95% confidence interval.

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