Placebo Effects and Clinical Trials of Neuropsychiatric Drugs

ABSTRACT

The placebo effect, a response observed during the placebo arm of a clinical trial, is produced by the psychobiological action of the placebo as well as by other potential contributors to symptom amelioration such as spontaneous improvement, regression to the mean, biases, concurrent treatments, and study design. From a psychological viewpoint, there are many mechanisms that contribute to placebo effects, including expectations, conditioning, learning, and anxiety reduction. Placebo responses are also mediated by opioid and non-opioid mechanisms including dopamine, serotonin, cholecystokinin, and immune mediators. During recent years, a trend towards increased placebo effects in clinical trials of neuropsychiatric drugs has been noted. Indeed, the placebo effects observed in clinical trials constitute an increasing problem and interfere with signal-detection analyses of potential treatments. Several potential factors including protocol/study design and conduct related factors may account for the placebo effect observed in clinical trials. This paper reviews key issues related to this problem and aims to identify potential solutions.