First-Pass Metabolism
The reduction in drug concentration that occurs when an orally administered drug is absorbed from the gut and passes through the liver before reaching systemic circulation.
In Depth
Oral cannabinoids undergo extensive first-pass metabolism in the liver. THC is converted to 11-OH-THC (which is more potent than THC and crosses the blood-brain barrier more readily) and then to 11-COOH-THC. This explains why oral cannabis produces a different, often more intense and longer-lasting effect than inhaled cannabis at equivalent doses. CBD oral bioavailability is only 6–20% due to first-pass metabolism. Sublingual and buccal routes partially bypass first-pass metabolism.
More in Pharmacology
Endocannabinoid System (ECS)
A lipid-based retrograde neurotransmitter system comprising endogenous cannabinoids (endocannabinoids), their receptors (CB1, CB2), and metabolic enzymes.
CB1 Receptor
Cannabinoid receptor type 1. A G protein-coupled receptor (GPCR) primarily expressed in the central nervous system. The primary target of THC's psychoactive effects.
CB2 Receptor
Cannabinoid receptor type 2. A GPCR primarily expressed in immune tissues and peripheral organs. Less abundant in the CNS than CB1.
Anandamide (AEA)
N-arachidonoylethanolamine. The first endocannabinoid identified. A partial agonist at CB1 and CB2 receptors, named from the Sanskrit word "ananda" meaning bliss.
2-Arachidonoylglycerol (2-AG)
The most abundant endocannabinoid in the brain. A full agonist at both CB1 and CB2 receptors.