Which organ is primarily responsible for drug metabolism?

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

Answer: (A)

Drug metabolism is mainly carried out by the liver because it contains a high concentration of drug‑metabolizing enzymes, especially the cytochrome P450 family, along with numerous Phase I and Phase II enzymes. These enzymes transform lipophilic drugs into more polar, water‑soluble forms through oxidation, reduction, hydrolysis (Phase I) and then conjugation with glucuronide, sulfate, or other groups (Phase II). This biotransformation often enables subsequent elimination by the kidneys or biliary system and can also affect a drug’s activity and duration. While other organs can contribute to metabolism in certain cases—kiddneys handle many metabolites and some compounds are metabolized in the lungs or other tissues—the liver is the primary organ responsible for drug metabolism.