Antidepressant drugs and the response in the placebo group: the real problem lies in our understanding of the issue.

In a recent paper, Horder and colleagues (Horder et al., 2010, J Psychopharmacol 25: 1277-1288) have suggested that the mainproblem in the Kirsch analysis is methodological. We argue that the results are similar irrespective of the method used. In our opinion the data suggest that placebo and drug effects are non-additive: antidepressants act independently of depression severity, while the placebo effect is present only in milder cases. While the response in the placebo group is due to unstable 'noise' and 'artefacts', the medication effect is reliable, valid and stable.