The cannabinoid delta-9-tetrahydrocannabinol is the principal psychoactive ingredient of marijuana. Cannabinoid receptor 2(CNR2) and the cannabinoid receptor 1 (brain) (CNR1) gene have the characteristics of a guanine nucleotide-binding protein (G-protein)-coupled receptor for cannabinoids. They inhibit adenylate cyclase activity in a dosedependent, stereoselective, and pertussis toxinsensitive manner. These proteins have been found to be involved in the cannabinoidinduced CNS effects (including alterations in mood and cognition) experienced by users of marijuana. The cannabinoid receptors are members of family 1 of the G-protein-coupled receptors.