THC cannabis drug. Computer model of a molecule of the psychoactive drug tetrahydrocannabinol (THC), shown as the electrostatic potential surface. The drug is found in products derived from the hemp or cannabis plant (Cannabis sativa), such as marijuana or hashish, which can be smoked to produce rapid, short-lived effects of relaxation and euphoria. Cannabis is an illegal drug in many countries, though THC also has uses such as pain relief, in the form of the drug Dronabinol, for conditions such as MS (multiple sclerosis). The molecule's chemical formula is C21.H30.O2.