Tetrahydrocannabinol (THC), also known as delta-9-tetrahydrocannabinol (delta-9-THC), delta-1-THC, is the main psychoactive substance found in the cannabis plant. The pharmacological actions of THC involve the binding and activation of cannabinoid receptor CB1 in the central nervous system and the CB2 receptor in immune cells. THC is a partial agonist at these receptors and therefore they are not fully activated. Research into the mechanism of action of THC has led to the discovery of endogenous cannabinoids, namely anandamide.