The cannabinoid delta-9-tetrahydrocannabinol is the principal psychoactive ingredient of marijuana. The proteins encoded by this gene 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 dose-dependent, stereoselective, and pertussis toxin-sensitive manner. These proteins have been found to be involved in the cannabinoid-induced CNS effects (including alterations in mood and cognition) experienced by users of marijuana. Cannabinoid receptor 2 is a G protein-coupled receptor from the cannabinoid receptor family. It is closely related to the cannabinoid receptor 1 which is responsible for the psychoactive properties of tetrahydrocannabinol, the active principle of marijuana.