Smoking cannabis. Man lighting a hand-rolled cigarette (joint) containing cannabis. Cannabis is a drug derived from the leaves and flowers of the hemp plant (Cannabis sativa). It may consist of dried material (marijuana) or a resinous extract (hashish). It is usually mixed with tobacco and smoked, or it may be eaten. It is illegal in most countries. It produces feelings of relaxation, alters time perception and heightens the senses. Heavy use can cause psychological problems and lung disease.