ALCOHOL, narcotics, HALLUCINOGENS, and PSYCHOMOTOR STIMULANTS differ markedly one from the other in terms of pharmacology and neurobiological mechanisms, dependence liability, legal and social restraints, expectations and cultural traditions. No general and unifying principle applies to all these substances, and it wouldbe misleading to extrapolate from the conditions that promote violence in individuals under the influence of alcohol to those with other drugs. Different types of drugs interact with aggressive and violent behavior in several direct and indirect ways from (1) direct activation of brain mechanisms that control aggression, mainly in individuals who have already been aggressive in the past; (2) drug states, such as alcohol or hallucinogen intoxication, serving as license for violent and aggressive behavior; (3) drugs such as heroin or cocaine serving as commodities in an illegal distribution system, drug trafficking, that relies on violent enforcement tactics; to (4) violent behavior...