The term nocebo (Latin nocēbō, "I shall harm", from noceō, "I harm") was coined by Walter Kennedy in 1961 to denote the counterpart to the use of placebo (Latin placēbō, "I shall please", from placeō, "I please"; a substance that may produce a beneficial, healthful, pleasant, or desirable effect).
Kennedy emphasized that his use of the term "nocebo" refers strictly to a subject-centered response, a quality inherent in the patient rather than in the remedy"
In the narrowest sense, a nocebo response occurs when a drug-trial subject's symptoms are worsened by the administration of an inert, sham, or dummy (simulator) treatment, called a placebo.
According to current pharmacological knowledge and the current understanding of cause and effect, a placebo contains no chemical (or any other agent) that could possibly cause any of the observed worsening in the subject's symptoms.
Thus, any change for the worse must be due to some subjective factor. Adverse expectations can also cause the analgesic effects of anesthetic medications to disappear.