Which organ primarily processes many drugs during metabolism?

• A. Kidneys
• B. Lungs
• C. Liver
• D. Skin

Answer: (C)

Most drug metabolism occurs in the liver because it contains the enzymes that chemically modify medications, making them easier to eliminate. In the liver, drugs undergo phase I reactions—like oxidation, reduction, and hydrolysis—primarily via cytochrome P450 enzymes—followed by phase II reactions that attach polar groups to increase water solubility. This biotransformation helps prepare drugs for excretion in urine or bile. The liver also receives drugs from the gut through the hepatic portal vein, so many medications experience first-pass metabolism before reaching systemic circulation. Other organs contribute only to a lesser extent—kidneys handle excretion, lungs metabolize a few compounds, and the skin has minimal metabolic activity—but the liver is the main site where drug metabolism happens.