The paper deals solely with iatrogenic disaster due to the misuse of therapeutic drugs prescribed or unprescribed, and its main purpose is to encourage a high index of suspicion that an unexpected apparently natural death may be iatrogenic due to the medicines administered before death. Toxic effect, side effect and adverse reaction are defined and particular attention is given to adverse effects induced by drug interaction and to the impact of disease and of the extremes of age on the potency of drugs. The deaths under discussion are "biochemical deaths" and as such are difficult to prove at post mortem examination especially if the forensic pathologist has not been made aware of the identity of drugs administered before death. Examples which are apt to create difficulties, particularly those due to drug interaction, are discussed, including oral hypoglycaemics, anticoagulants, anticonvulsants, antidepressants, hypotensives and cardiac glycosides. The solution to the problem is not to refrain from using necessary drugs, but to use them wisely with full awareness of the mechanisms whereby they can become lethal.