A population-based Danish data resource with possible high validity in pharmacoepidemiological research.

The incomplete understanding of drug effects at the time of marketing has led to ongoing epidemiological monitoring. The Danish National Health Service covers part of the expenses for most kinds of prescription drugs. The accounting system within the pharmacies is increasingly computerized. In 1992 we found that 96% of the pharmacies were computerized. The computerized accounting systems give no information about adverse drug effects, but this can be obtained from the Danish Hospital Register by cross-checking registries, and in some cases from the register of birth and the register of congenital malformations. There is a great need for new data sources in pharmacoepidemiology. In spite of some evident methodological problems, the Danish data sources probably have high validity compared with international sources, since they are population based.