a clinically significant response to a therapeutically inert substance or nonspecific treatment (placebo), deriving from the recipient’s expectations or beliefs regarding the intervention. It is now recognized that placebo effects accompany the administration of any drug (active or inert) and contribute to the therapeutic effectiveness of a specific treatment. For example, patients given a placebo to relieve headaches may report statistically significant reductions in headaches in studies that compare them with patients who receive no treatment at all. This term is also used more generally in nonclinical studies to indicate any effect arising from participants’ expectations regarding the study.