Dissociative drugs, such as Ketamine or PCP, alter a persons state of mind and mood but do not cause a person to hallucinate. Dissociative drugs cause a person to detach, or dissociate, from his or her surroundings. D-lysergic acid diethylamide (LSD) is the most potent hallucinogenic substance known to man. Dosages of LSD are measured in micrograms or millionths of a gram. By comparison, dosages of cocaine and heroin are measured in milligrams or thousandths of a gram. Compared to other hallucinogenic substances, LSD is 100 times more potent than psilocybin and psilocin and 4,000 times more potent than mescaline.