Also called pharmacogenetics – the use of human genetic variations to optimise the discovery and development of drugs and the treatment of patients. The human race varies much more in its genetic make-up than has previously been realised; these variations in GENES and their PROTEIN products could be utilised to provide safer and more e?ective drugs. Genes affect drug absorption, distribution, METABOLISM and excretion. Drugs are designed and prescribed on the basis of a population’s needs, but patients comprise a diverse range of individuals. For example, nearly one-third of patients fail to respond to the cholesterol-reducing group of drugs, the STATINS. Around half do not respond to the tricyclic ANTIDEPRESSANT DRUGS. Over 80 per cent of patients’ responses to drugs depends on their genetics: this genetic variation needs to be identi?ed so as to make the prescription of drugs more e?ective, and technology for analysing genetic variants is progressing. Assessing drug e?ectiveness, however, is not simple because the health and diets of individuals are di?erent and this can affect the response to a drug. Even so, the genetic identi?cation of people who would or would not respond to a particular drug should bene?t patients by ensuring a more accurately targeted drug and by reducing the risks to a person of side-effects from taking a drug that would not work. There would also be substantial economic savings.