In 2012, Leucht et al. (Reference Leucht, Hierl, Kissling, Dold and Davis2012) published a highly-cited meta-meta-analysis in which they claimed that effect sizes for psychiatric drugs in which they concluded that ‘psychiatric drugs were not generally less efficacious than other drugs,’ along with the seemingly contradictory caveat that ‘Any comparison of different outcomes in different diseases can only serve the purpose of a qualitative perspective. The increment of improvement by drug over placebo must be viewed in the context of the disease's seriousness, suffering induced, natural course, duration, outcomes, adverse events and societal values’ (p.97). In an interesting follow-up to this paper, Cristea and Naudet (this issue) examined citations of the Leucht et al. article and concluded that most of them ignored Leucht et al.’s caveats and had used the citation to claim that the effects of psychiatric medications were similar to those of treatments in general medicine.

Whereas in 2012, Leucht and colleagues reported effects sizes for general medicine to be similar to those found in psychotropic medications, in 2015, they reported effect sizes in general medicine that are substantially larger than those for psychiatric drugs (Leucht et al. Reference Leucht, Helfer, Gartlehner and Davis2015). For example, the drug-placebo SMDs reported by Leucht et al. (Reference Leucht, Hierl, Kissling, Dold and Davis2012) for antidepressants in the treatment of major depressive disorder are about 0.32. This is larger than the effect sizes reported by Leucht et al. (Reference Leucht, Helfer, Gartlehner and Davis2015) for statins (SMD  =  0.15) and aspirin (SMD  =  0.12) for the prevention of cardiovascular events, but considerably smaller than the effect sizes reported for proton pump inhibitors (SMD  =  1.39), oxycodone plus paracetamol (SMD  =  1.04) and levodopa (SMD  =  0.93) in treating gastric reflux, post-operative pain and Parkinson's disease, respectively. However, these data must be interpreted in light of Leucht et al.’s caution about comparisons between outcomes across different conditions. The more important question to answer is whether drug-placebo differences within particular disorders are clinically important. Cristea and Naudet make the claim that the effects of psychiatric treatments are ‘trivial.’ In this commentary, I consider whether that conclusion is justified.

Cristea and Naudet's conclusion that the effect of psychiatric drugs are trivial is based on the conventional classification that standardised mean differences (SMD) of 0.20 as small, those of 0.50 as a medium, and those of 0.80 as large (Cohen, Reference Cohen1988). However, Cohen proposed his cut-offs for small, medium and large effect sizes with ‘invitations not to employ them if possible. The values chosen had no more reliable a basis than my own intuition’ (p. 532). More meaningful criteria for clinical significance of drug-placebo difference have to be set independently for each disorder. How can this be done?

Researchers in the field of chronic pain reduction have reached a consensus on the clinical significance of treatment-induced pain reduction can be assessed within their field, and their method of so doing can provide a model for other fields (Farrar et al. Reference Farrar, Young, LaMoreaux, Werth and Poole2001; Dworkin et al. Reference Dworkin, Turk, Farrar, Haythornthwaite, Jensen, Katz and Witter2005). The most common primary outcome measure in clinical trials of chronic pain is a 0–11 numerical rating scale (NRS) of pain intensity. To establish criteria for clinical significance, Farrar and colleagues compared NRS ratings with Patient Global Impression of Change scale, a 7-point scale, with endpoints of ‘very much worse and very much improved’ and ‘very much worse,’ with ‘no change’ as the midpoint. They decided in advance, that a score of ‘much improved’ would be their criterion for clinical significance, and established that this corresponded to a NRS reduction of 2 points or 30%. These, then, became conventionally accepted criteria for clinical improvement in chronic pain.

What would happen if this strategy were employed to evaluate the clinical significance of changes in symptoms of depression? The most commonly used scale for assessing levels of depression is the Hamilton Rating Scale for Depression (HRSD). Leucht et al. (Reference Leucht, Fennema, Engel, Kaspers-Janssen, Lepping and Szegedi2013) have provided the data needed to establish empirically derived criteria for the clinical significance of HRSD differences, using the approach adopted by chronic pain researchers (Moncrieff & Kirsch, Reference Moncrieff and Kirsch2015). These data indicate that ‘much improved’ is equivalent to a 14-point improvement on the HRSD, minimally improved is equivalent to a 7-point difference, and the mean rating for ‘no change’ is 3-points improvement on the HRSD. These correspond to effect sizes of SMDs of 0.21 for ‘no change,’ 0.74 for ‘minimally improved,’ and 1.37 for ‘much improved.’ A 3-point improvement on the HRSD or effect size of 0.50 was proposed by the National Institute of Health and Care Excellence (NICE, 2004), which sets official treatment guidelines for the National Health Service in the UK. Leucht's data reveal these criteria to be equivalent to no difference at all for HRSD scores and well below a minimal difference for effect sizes (Moncrieff & Kirsch, Reference Moncrieff and Kirsch2015).

Thus, using empirically derived criteria for clinical significance, the difference in outcome between antidepressants and placebo is indeed trivial, as claimed by Cristea and Naudet. It does not come close to what would be considered a minimal difference in global ratings of improvement, let alone the ‘much improved’ criterion consensually adopted for evaluating the clinical significance of pain medications. On the other hand, a recent meta-analysis indicates that antidepressant medication has been shown to increase the risk of serious adverse events (Jakobsen et al. Reference Jakobsen, Katakam, Schou, Hellmuth, Stallknecht, Leth-Møller and Gluud2017). As concluded by the authors of that analysis, ‘the potential small beneficial effects seem to be outweighed by harmful effects’ (p. 2).