A placebo is something of no intrinsic remedial value that is used to appease or reassure another. The placebo effect is related to the perceptions and expectations of the patient; if the substance is viewed as helpful, it can heal, but, if it is viewed as harmful, it can cause negative effects. . The term placebo has been used in medicine since the 18th century and has changed from “an epithet given to any medicine adapted more to please than to benefit the patient” in Quincy’s Lexicon-medicum to Irving Kirsch’s hypothesis that placebo effects are produced by the self-fulfilling effects of response expectancies, in which the belief that one will feel different leads a person to actually feel different.
If you broaden the concept of a placebo beyond pure medical treatment, you can start to include other interventions, such as strapping, dietary supplements, acupuncture and other ergogenic aids as types of placebos. In many cases these interventions have no scientific evidence to prove or dis-prove their effect on the individual and instead the placebo effect may be the cause of change
The brain has control over the body processes affected by most placebos, such as pain, motor fatigue, and fever. These body processes are directly organised by the brain, while other processes usually regulated by the body such as the immune system are also controlled indirectly by the brain through the nervous system. Moerman and Jonas introduced the term “meaning response” for the meaning that the brain associates with the placebo, which causes a physiological placebo effect as a placebo is an inert substance that does not directly cause anything.
Kirsch, I., 1985. Response expectancy as a determinant of experience and behaviour. American Psychologist 40 (11):1189-1202
Moerman, D.E. and Jonas, W.B. 2002. Deconstructing the placebo effect and finding the meaning response. Ann Intern Med. 136 (6): 471–6