Adverse reactions to drugs

Abstract An adverse effect is an unwanted effect of a drug. Adverse effects can be due to either toxic effects or side effects. A toxic effect is an adverse effect that arises through an exaggeration of the same pharmacological effect that is responsible for the therapeutic effect of the drug, for example hypokalaemia due to diuretic therapy, and is therefore dose related. A side effect is an adverse effect that arises through some pharmacological action other than that which produces the therapeutic effect; such effects may be dose related (for example anticholinergic effects of tricyclic antidepressants) or not dose related (for example a rash associated with an antibiotic). Because dose-related side effects can also be regarded as toxic effects, it is better to avoid the terms ‘toxic effects’ and ‘side effects’ and to use instead the term ‘adverse effects’, which covers all types of unwanted effects.