Harms from medicines: inevitable, in error or intentional.

Rational therapeutics requires a balance between benefits and harms. (i) Harm may be inevitable. Some adverse drug reactions cannot be predicted or prevented. (ii) Some harm occurs in error when a medicine is wrongly formulated, prescribed, dispensed or administered. Adverse drug reactions that might have been prevented, for example, by monitoring, fall into this category. (iii) Rarely, harm is inflicted deliberately, for example, in murder by poisoning. Here I consider adverse drug reactions, errors and deliberate drug-induced harm from the perspective of a clinical pharmacologist.