Which organ is primarily responsible for drug metabolism and detoxification?

• A. The kidneys
• B. The liver
• C. The heart
• D. The lungs

Answer: (B)

The liver is the main organ for drug metabolism and detoxification because it houses a rich set of enzymes, especially the cytochrome P450 system, that chemically transform many drugs. Through Phase I reactions (oxidation, reduction, hydrolysis) the molecule is often made more reactive or exposed functional groups. Then Phase II reactions (conjugation such as glucuronidation, sulfation, acetylation) attach polar groups, making the drug more water-soluble for easier elimination. This process often reduces a drug’s effect and prepares it for excretion, with the first-pass effect on many oral drugs limiting how much reaches systemic circulation initially. While the kidneys excrete metabolites and the lungs can perform minor metabolic roles, and the heart does not metabolize drugs, the liver remains the primary site for both transformation and detoxification of many medications.