Adverse Effect or Reaction:
An
abnormal, unexpected, infrequent and usually unpredictable injurious response to a
drug. Used in this restrictive sense, the term
adverse reaction does NOT include
effects of a drug which are normally a part of its
pharmacological action, even though such effects may be
undesirable and
unintended. Adverse reactions are of three
basic types: those due to
drug allergy, those caused by individual
idiosyncrasy and those representing
toxic effects of drugs on
tissue structure and function.
--From The Essential Guide to Perscription Drugs