The following pharmacology definition has been taken from the Pharmacology and Experimental Therapeutics Department Glossary at Boston University School of Medicine.
A qualitatively abnormal or unusual response to a drug which is unique, or virtually so, to the individual who manifests the response. “Idiosyncratic Response ” usually applies to a response that is not allergic in nature and cannot be produced with regularity in a substantial number of subjects in the population, and which is ordinarily not produced in a greater intensity in an individual, or in a greater fraction of the population, by the expedient of increase in the dose. In other words, were frequency or intensity of idiosyncratic response used as a measure of effect in constructing a dose-effect curve, a curve might indeed be constructed, but its slope would be found to be 0 (zero), indicating that effect was not significantly a function of dose. In practice, the mechanism of production of an idiosyncratic response is unknown; once the mechanism is known, the response can usually be classified in some other way.
The copyright of the text is hold by Trustees of Boston University. Permission has been granted for its use in this blog.