Carlo Marchesi, Chiara De Panfilis, Matteo Tonna, Paolo Ossola

For many years, placebo has been defined by its inert content and use in clinical trials. In recent years, several studies have demonstrated its effect in the treatment of major depression. The aim of this paper is to present the conclusions of recent meta-analyses of the placebo effect in major depression, to explain the mechanism by which placebo exerts its effect, and to discuss whether placebo can be used in the treatment of patients with major depression in clinical practice. Recent meta-analyses have demonstrated that the placebo effect is estimated to account for 67% of the treatment effect in patients receiving antidepressants, and furthermore that placebo is as effective as antidepressants in patients with mild to moderate major depression (reporting a Hamilton Depression Rating Scale score lower than 25), whereas placebo is less effective than antidepressants in severely depressed patients. However, several limitations make the translation of these conclusions into clinical practice impracticable. Clinicians should learn from the "placebo lesson" to maximize the nonspecific effects of treatment when they prescribe an antidepressant, particularly in less severely depressed patients, who show a higher placebo response in randomized controlled trials. This strategy can increase the antidepressant effect and may reduce nonadherence with treatment.