The study of how genes affect the actions of drugs. The enormous growth in knowledge about human genetics arising from the Human Genome Project, coupled with the rapid advance of computer systems to analyse the vast amounts of data, has revolutionized drug discovery and development. This approach, which combines genomics and pharmacology, improves understanding of drug actions, suggests new potential drug molecules, and enables computer-based searches for likely drug targets. In addition, analysis of genetic data from individuals raises the prospect of drugs being tailor-made to suit the genetic make-up of particular patients or groups of patients. This more precise targeting of drugs should make drugs more effective, with less risk of adverse side effects.