The serious nature of adverse drug reactions (ADRs) has been highlighted in a number of instances over the last forty years, the most recent of these being the occurrence of serious thrombotic events with the use of COX-2 inhibitors. ADRs are estimated to be between the 4th and 6th leading cause of death in the USA, with fatal ADRs occurring in 0.32% of patients. A recent UK study showed that 6.5% of hospital admissions were related to ADRs. ADRs can therefore be regarded as a significant public health and economic problem. There is an urgent need to develop better preventive strategies to reduce the burden of ADRs. Because ADRs can affect any bodily system, can have many different clinical presentations, and are of widely variable severity, prevention will not be easy and will have to be multifactorial in its approach. This paper reviews the epidemiology of ADRs in hospitals and evaluates the research that has been undertaken to date to prevent ADRs.