Pharmacogenetics is an evolving field that provides the link between an individual's genetic code and drug metabolism and drug response. This field offers the great promise of individualized medication selection and optimized dosage to maximize treatment response and to minimize adverse side effects. As our understanding of the role of the effects of genetic variants on drug metabolism and body drug processing grows, so does our ability to educate and inform our patients about expected treatment response to the medications being prescribed to them. This brief review will provide an overview of genetics, pharmacogenetics, and current and future examples of genetic variants predicting drug response in gastrointestinal disease, and the limitations and the promise of this exciting and developing field.