The use of medicines can never be 100% safe, or 100% effective, and therefore each prescription is a balance of the intended benefits from using the medication versus the risks associated with it. Any patient using medicines may experience only the positive effects, only the negative effects, a combination of both positive and negative effects or no effects at all. The negative effects of medicines are referred to as ‘adverse drug reactions’ (ADRs) and are officially defined as ‘A response to a medicinal product which is noxious and unintended’.1 A negative symptom or effect of a medicine may be categorised as an ADR regardless of how a drug has been used, and so includes abuse, overdose, industrial exposure, medication errors, and unlicensed and/or off-label use. To generate data on ADRs, including identification of previously unsuspected ADRs, the UK set up one of the world's first spontaneous reporting schemes for collecting SUSPECTED ADRs in 1964. These data were initially collected by doctors who would complete a yellow-coloured card found at the back of the British National Formulary (BNF). Fifty years later, although the range of potential reporters and means of completion have evolved, the ‘Yellow Card’ Scheme continues to be a vitally important mechanism to collect these data. To identify the rarest ADRs, national data may not be sufficient, and so the WHO Programme for International Drug Monitoring was established in 1968 and has been coordinated by the Uppsala Monitoring Centre (UMC) in Sweden since 1978. The UMC is a WHO collaborating centre currently collecting, … [Full text of this article]