CYP2C9 is a gene that provides instructions for making an enzyme involved in the metabolism of various drugs. This enzyme is part of the cytochrome P450 family, which plays a crucial role in breaking down medications in the liver. Variations in the CYP2C9 gene can affect how individuals process certain drugs, leading to differences in drug effectiveness and risk of side effects. People with specific genetic variations in CYP2C9 may require adjusted doses of medications, such as warfarin, a common blood thinner. Understanding a person's CYP2C9 genotype can help healthcare providers tailor treatments to improve safety and efficacy, ensuring better health outcomes.