[Adverse drug reactions definitions and terminology]

Any therapeutic substance is potentially harmful. There are many examples in the literature justifying the need to follow-up the drug throughout it's life cycle (post-marketing surveillance). It is estimated that only 50% of the undesirable reactions can be detected during the pre-marketing clinical trials. The drugs' manufacturers have the obligation to report any unwanted reaction or effect of a drug to the regulatory authorities. Furthermore, the regulatory authorities encourage physicians to report adverse effects immediately. The terminology used in these reports contains many different terms which describe an undesired reaction: adverse drug reaction, adverse event, adverse effect and side effect. The common definition of "Adverse Drug Reaction" (ADR) is: "A response to a drug which is noxious and unintended and which occurs at doses normally used in man for prophylaxis, diagnosis, or therapy of disease, or the modification of physiological function." The use of many terms for the description of the same kind of event causes disharmony and difficulties in analysis. It is of utmost importance to use compatible terms in order to achieve accord throughout the development process and marketing of a drug. Today, adverse-drug-reaction reporting is of major importance in the regulatory authorities' agenda and the regard for drug safety is rising. The aim of this review is to introduce the various terms used to describe ADR's, to discuss their advantages and shortcomings and the differences between them.