Tetrahydrocannabinol (
THC) is the principal psychoactive constituent of cannabis and one of at least 113 total cannabinoids identified on the plant. Although the chemical formula for THC (C
21H
30O
2) describes multiple isomers, the term
THC usually refers to the Delta-9-THC isomer with chemical name
(â)-trans-Î9-tetrahydrocannabinol. Like most pharmacologically active secondary metabolites of plants, THC is a lipid found in cannabis, assumed to be involved in the plant's evolutionary adaptation, putatively against insect predation, ultraviolet light, and environmental stress.