What organ is primarily responsible for drug metabolism?

The liver is the primary organ responsible for drug metabolism due to its unique role in biotransformation processes. It contains a variety of enzymes, particularly the cytochrome P450 family, which are crucial in modifying drugs to make them more water-soluble. This modification facilitates their excretion from the body, either through the urine or bile. The liver's extensive blood supply allows it to efficiently process substances absorbed from the gastrointestinal tract, making it a central hub in the metabolism of both pharmaceutical drugs and endogenous compounds.

In contrast, while the kidneys play a significant role in the elimination of drugs and their metabolites from the body through urine, they are not primarily involved in the metabolic transformation of drugs. Similarly, the blood serves as a transport medium for drugs but does not partake in their metabolism. The lungs can metabolize certain substances (including some inhaled drugs) but are not the primary site for drug metabolism overall, with the liver remaining the most vital organ for this function.