Drug metabolism occurs primarily in which organ?

• A. Liver
• B. Kidney
• C. Lungs
• D. Brain

Answer: (A)

Drug metabolism is the body's process of transforming drugs into more water-soluble forms to facilitate elimination. The liver is the main site because it houses a high concentration of metabolizing enzymes, especially the cytochrome P450 family, along with many conjugating enzymes that handle both phase I and phase II reactions. After oral administration, the liver also performs first-pass metabolism, reducing the amount of drug that reaches systemic circulation. While other organs can contribute in specific cases—some metabolism occurs in the kidneys, lungs, or gut, and the brain is not a major site for metabolic processing—the liver handles the majority of drug metabolism. Disorders of liver function or interactions that alter hepatic enzyme activity can significantly impact drug clearance, underscoring why the liver is the best answer.