Abstract Pharmacogenetics and pharmacogenomics are related areas of research that aim to determine the relationship between genotypic variation, including changes in gene expression, and variations in drug response seen across patient groups. Understanding the genetic bases of variability in drug response due to altered pharmacokinetics (e.g., drug absorption, distribution, metabolism, excretion) or pharmacodynamics (e.g., drug receptor up- or downregulation) is essential for the practitioner to fully anticipate, recognize, and mitigate potential drug toxicity or ineffectiveness. The ultimate goal of pharmacogenetics and pharmacogenomics is to develop personalized medicine for individuals by leveraging knowledge of phenotypic variation in drug response due to genetic mutations, polymorphisms, or gene expression.