THC cannabis drug molecule. Animated molecular model of the psychoactive drug tetrahydrocannabinol (THC), seen rotating above its reflection. This 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 is used in medicine as pain relief for conditions such as MS (multiple sclerosis). The molecule's chemical formula is C21.H30.O2. The atoms are colour-coded: carbon (black), hydrogen (blue), and oxygen (red).