Understanding and assessing adverse drug reactions.

Establishing causality between a medication exposure and the development of an adverse event (AE) is a difficult process. If a causal relationship can be confirmed, an AE is referred to as an adverse drug reaction (ADR). The reported signs or symptoms of an AE could be due to the drug, the underlying disorder, or other unrelated or concurrent factors. The conventional approach to defining ADRs is based on a clinical judgment that the link between drug exposure and AE is definite, probable, possible, or doubtful. The validity and reliability of this assessment varies according to the knowledge, background, and experience of the clinician making the assessment. A systematic and validated method for estimating the probability of an ADR has been described by Naranjo et al. This method solicits answers to 10 questions; the total score is then used to quantify the probability of an ADR.