Absorption, distribution, metabolism and excretion (ADME)

ADME describes the four stages a substance passes through in the body: absorption into the bloodstream, distribution to tissues, metabolism into other compounds, and excretion.

Pharmacologists use the ADME framework to explain why the same amount of a compound can produce different blood levels in different people. Absorption depends on the route, the formulation, and whether food is present. Distribution describes where the compound travels once it is in circulation, including how much binds to proteins or settles into fatty tissue. Metabolism, largely in the liver, converts the compound into metabolites, and excretion removes those metabolites through urine, feces, or bile.

For cannabidiol, each stage carries its own variability. CBD is fat-soluble, is absorbed inconsistently when swallowed, is processed by cytochrome P450 enzymes, and is stored in fat before it is cleared. Readers meet ADME language in pharmacokinetic study summaries and in discussions of drug interactions, where the metabolism stage is usually the point of concern. Understanding the four stages makes it easier to see why published research often reports wide ranges rather than a single number.