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Mental health
What is the threshold for a clinical minimally important drug effect?
  1. Michael P Hengartner
  1. Department of Applied Psychology, Zurich University of Applied Sciences, Zurich, Switzerland
  1. Correspondence to Dr Michael P Hengartner, Department of Applied Psychology, Zurich University of Applied Sciences, Zurich Switzerland; michaelpascal.hengartner{at}zhaw.ch

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Dr Adlington1 recently drew attention to the uncritical promotion of antidepressant drugs by various key opinion leaders and news outlets following the publication of a large meta-analysis by Cipriani and colleagues.2 She also pointed out that the small effect sizes were largely neglected and that most news report did not differentiate mild depression from severe depression. The crucial issues thus are whether the effects of antidepressants are clinically relevant and whether these drugs also work in mild to moderate depression.

A leading psychiatric journal recently published a meta-analysis, coauthored by Dr Cipriani, in which the authors purport that their findings demonstrate efficacy of newer generation antidepressants in both mild to moderate and severe depression.3 This article was accompanied by an editorial entitled, ‘The alleged lack of efficacy of antidepressants in non-severe depression: a myth debunked’.4 Obviously, commentators and authors want to disseminate the message that antidepressants are an effective treatment for mild to moderate depression and that practice guidelines should incorporate these findings. However, neither the original paper3 nor the editorial4 does in fact provide evidence that the drugs are clinically effective for any form of depression. Instead, their conclusion appears to rely exclusively on the fact that there is a statistically significant drug-placebo difference in mean symptom change. The same misinterpretation of statistical significance also appears to have fuelled the simplistic and overoptimistic conclusions drawn from the Lancet meta-analysis by Cipriani et al.2

In the following, I will summarise the most recent meta-analytic findings and ponder on the reported average treatment effect. Equating statistical significance with a proof of drug efficacy is a scientific fallacy and I propose that a drug-placebo difference of this magnitude is evidence of a lack of efficacy.

Research question, findings and conclusions

The recent meta-analysis by Furukawa et al 3 …

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