A placebo is a preparation which is pharmacologically inert but which may have a medical effect based solely on the power of suggestion, a response known as the placebo effect or placebo response. It may be administered through ingestion, injection, inhalation, insertion into a body cavity, or applied topically.
Sometimes known as non-specific effects or subject-expectancy effects, a so-called placebo effect occurs when a patient's symptoms are altered in some way (i.e., alleviated or exacerbated) by an otherwise inert treatment, due to the individual expecting or believing that it will work. Some people consider this to be a remarkable aspect of human physiology; others consider it to be an illusion arising from the way medical experiments are conducted.
The placebo effect occurs when a patient takes an inert substance (“a sugar pill”) in conjunction with the suggestion from an authority figure that the pill will aid in healing and the patient’s condition improves. This effect has been known for years.