Morphine and human aggression

Twenty-eight male undergraduates received either 45 mg of immediate-release oral morphine tablets or a placebo. Subjects were then given the opportunity to administer electric shocks to an increasingly aggressive bogus opponent during a competitive reaction-time task. Subjects in the morphine condition were more willing to initiate attacks against their opponent than subjects in the placebo condition, and reacted more aggressively at all levels of provocation.