Mechanisms of Action and Pharmacokinetics of Cannabis
At least 100 cannabis species are compounds known as cannabinoids, a molecule with a 21-carbon terpenophenolic skeleton. Cannabinoids produce more than 100 naturally occurring chemicals, the most abundant of which are Δ-9-tetrahydrocannabinol (THC), cannabidiol (CBD), terpenes, and flavonoids. THC and CBD bind with cannabinoid receptors (CB1 and CB2), which are present in the brain and many organs. Metabolism of cannabis is determined by the route of consumption. When inhaled, THC and its metabolites enter the bloodstream rapidly via the lungs; they achieve peak levels within 6 to 10 minutes and reach the brain and various organs. The bioavailability of inhaled THC is 10% to 35%. After THC is absorbed, it travels to the liver where most of it is eliminated or metabolized to 11-OH-THC or 11-COOH-THC. The remaining THC and its metabolites enter the circulation. The bioavailability of ingested THC is only 4% to 12%. THC is highly lipid soluble and is therefore rapidly taken up by fat tissue. The plasma half-life of THC is 1 to 3 days in occasional users and 5 to 13 days in chronic users. The bioavailability of CBD via inhalation is 11% to 45%, whereas that of oral CBD is 6%. CBD has high lipophilicity and therefore is rapidly distributed in the brain, adipose tissue, and other organs. CBD is hydroxylated to 7-OH-CBD and 7-COOH-CBD by cytochrome P450 enzymes CYP3A4 and CYP2C9 in the liver and is excreted mainly in feces and less in urine. The plasma half-life of CBD is 18 to 32 hours.
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