Unintended, deleterious effects of otherwise licit, therapeutic, properly administered drugs; for effects of illicit and abused drugs, or of environmental chemicals, see toxicology or poisoning.

An adverse drug reaction (ADR) is a harmful, unintended result caused by taking medication.: 1.1 Adverse Drug Reaction (ADR)  ADRs may occur following a single dose or prolonged administration of a drug or may result from the combination of two or more drugs. The meaning of this term differs from the term "side effect" because side effects can be beneficial as well as detrimental...