Difficulties in assessing the adverse effects of drugs.

1 In recent years the phenomenon of the adverse drug reaction (ADR) has become a focus of increased attention and research, and we have become aware of the clinical complexity of the phenomenon and some of the difficulties inherent in assessing adverse effects. Evidence for such difficulties includes the discrepancies in figures for ADR incidence in epidemiological studies, the non-specificity and suggestibility of ADR symptoms, and the substantial disagreements, even among experts, in the diagnosis of ADRs. 3 An observed clinical manifestation heavily depends on the clinical setting and on the intent of the clinician, and the large number of factors that many confound the link between a given manifestation and an administered drug. A diagnostic algorithm, or branched logic decision format, has recently been developed. It comprises six axes of decision strategy and provides standardized, operational rules for rating the probability of an ADR.