Pharmacogenomics is the study of genome in drug response.  It deals with the influence of acquired and inherited genetic variation on drug response in patients by correlating gene expression or single-nucleotide polymorphisms with pharmacokinetics and pharmacodynamics. There are several known genes which are largely responsible for variances in drug metabolism and response. The focus of this article will remain on the genes that are more widely accepted and utilized clinically for brevity. They are Cytochrome P450s, VKORC1, and TPMT. Patient genotypes are usually categorized into Ultra-rapid metabolizer, Extensive metabolizer, Intermediate metabolizer, Poor metabolizer. A potential role pharmacogenomics may play would be to reduce the occurrence of polypharmacy. It is theorized that with tailored drug treatments, patients will not have the need to take several medications that are intended to treat the same condition. Toxicogenomics is a sub discipline of pharmacology that deals with the collection, interpretation, and storage of information about gene and protein activity within a particular cell or tissue of an organism in response to exposure to toxic substances.