Tetrahydrocannabinol (THC) is one of at least 113 cannabinoids identified in cannabis. THC is the principal psychoactive constituent of cannabis. With chemical name (?)-trans-??-tetrahydrocannabinol, the term THC also refers to cannabinoid isomers. Like most pharmacologically active secondary metabolites of plants, THC is a lipid found in cannabis, assumed to be involved in the plant’s self-defense, putatively against insect predation, ultraviolet light, and environmental stress.