Drug metabolism refers to the biochemical transformation of drugs into more water-soluble compounds for easier elimination from the body. It mainly occurs in the liver through enzymatic reactions. Several physiological, pathological, genetic, and environmental factors influence the rate and extent of drug metabolism. Age is an important factor affecting drug metabolism. In newborns and infants, hepatic microsomal enzymes are not fully developed, resulting in slower metabolism of many drugs. In elderly individuals, liver mass, hepatic blood flow, and enzyme activity decrease, leading to prolonged drug action and accumulation. Genetic factors significantly influence metabolic activity. Genetic polymorphism of drug-metabolizing enzymes causes variation among individuals. Some people are slow metabolizers while others are rapid metabolizers. Variations in cytochrome P450 enzymes affect the metabolism of drugs such as isoniazid, warfarin, and phenytoin. Sex differences may alter metabolism due to hormonal influences. Certain drugs are metabolized more rapidly in males than females because of differences in liver enzyme activity and body composition. Species and racial differences also influence metabolism. Animals metabolize drugs differently from humans. Among humans, ethnic variations in enzyme activity can modify drug response and toxicity. Liver function