Cannabis, commonly known as marijuana and by numerous other names,a is a preparation of the cannabis plant intended for use as a psychoactive drug and as medicine. Pharmacologically, the principal psychoactive constituent of cannabis is tetrahydrocannabinol ; it is one of 483 known compounds in the plant, including at least 84 other cannabinoids, such as cannabidiol , cannabinol , tetrahydrocannabivarin , and cannabigerol .