"O God, that men should put an enemy in their mouths to steal away their brains!" complained Othello.
Since long before Shakespeare, it's been assumed that people are more aggressive when "under the influence" of alcohol and other drugs. In fact, drug use is often associated with aggressive acts such as rape and assault. But correlational data don't reveal whether drug use actually causes aggression.
That's why psychologist Brad Bushman has drunk deep studies of drug-related human aggression. The verdict: In many cases it does cause aggression.
Alcohol and other central nervous system (CNS) depressants such as barbiturates are clearly linked with aggression. In fact, the difference in aggression levels between drinkers and nondrinkers is about equal to the difference in physical aggression levels between males and females. Which is to say, major.
"If I had to bet the ranch on anything," says Bushman, "it would be that CNS depressants do increase aggression. It's harder to tell with other drugs because there aren't as many studies, but they also seem to."
CNS stimulants, like nicotine, caffeine, and amphetamines, have no consistent effect on aggression. Of the opiates, which cause euphoria and reduce pain, only codeine's been tested, and it upped aggressiveness. Marijuana, a hallucinogen, raises hostility.