A guide to the pharmacology of placebos.

The placebo effect is capable of relieving pain in a substantial proportion of patients; affective disorders also respond to the administration of inert medication. Changes in objective measures, such as blood pressure and blood glucose levels, demonstrate the action of placebos. The underlying mechanisms are not yet known, but because the nature and strength of the placebo response are governed by the patient's perceptions, both positive and negative results may be obtained. The complexity of human perception has made it extremely difficult to characterize the people who react. In clinical situations the placebo may be underused as a therapeutic agent, while in clinical trials the effect may be inadequately evaluated; the power and nature of the placebo effect truly warrant greater recognition.