CANNABIS EXPLAINER
How THC Is Metabolized
THC undergoes extensive liver metabolism before being excreted over days or weeks.
CANNABIS EXPLAINER
THC undergoes extensive liver metabolism before being excreted over days or weeks.
When cannabis is inhaled, THC crosses from the lungs directly into the bloodstream. When eaten, THC is absorbed through the intestinal wall and transported to the liver via the hepatic portal vein before entering systemic circulation. This "first-pass metabolism" in the liver produces 11-hydroxy-THC (11-OH-THC) — a more potent and longer-lasting psychoactive metabolite — before THC reaches the brain. This explains why edibles feel stronger.
The liver uses cytochrome P450 enzymes (primarily CYP2C9, CYP2C19, and CYP3A4) to metabolize THC. The primary pathway: THC → 11-hydroxy-THC (11-OH-THC) → 11-nor-9-carboxy-THC (THC-COOH). THC-COOH is the primary inactive metabolite and the main compound detected in urine drug tests. It is further broken down into THC-COOH glucuronide, a water-soluble conjugate that is excreted in urine.
After entering the bloodstream, THC is rapidly distributed throughout the body. The lipophilic nature of THC means it accumulates strongly in fat tissue, the brain, liver, and lungs. Blood levels of THC drop quickly as it moves out of circulation into tissues. THC stored in fat tissue is slowly released back into the bloodstream over days to weeks, sustaining elevated urinary metabolite levels long after the last use.
Approximately 65% of THC metabolites are excreted in feces via bile, and 20% in urine. Trace amounts are expelled through sweat, saliva, and breath. Urinary excretion is primarily as THC-COOH glucuronide. The elimination half-life of THC in plasma is approximately 1-3 days for acute use, but the terminal half-life for regular users can be 5-13 days due to redistribution from fat stores. This explains the wide range in detection windows.