Pharmacogenetics is the study of how genetic variables impact individual differences in drug safety and effectiveness. Pharmacogenomics is a rapidly growing field of science that combines pharmacology, the study of drugs, with genomics, the study of genes, in order to create safe, effective doses of medication that are specifically adapted to each patient's genetic profile. Basically, for more than 50 years, the idea of pharmacogenetics remained unknown. Pharmacogenomics applications can be used to improve the discovery of new entities and their development in two different ways: first, by developing new entities to combat drug resistance or new drug targets, and second, by improving the pharmacokinetics and metabolism of existing entities to minimise drug level variations