Aggressive behaviour is associated with negative mood and poor impulse control. Serotonin has been specifically associated with impulse regulation and deficiencies in serotonin have been linked to impulsive aggression. However, aggression occurs in a social context and noradrenaline has been implicated in social motivation. Both serotonergic and noradrenergic antidepressants may therefore be effective in reducing aggression. The evidence for the effects of antidepressants on aggression comes from a wide range of sources but there are few controlled trials or experimental studies. Current findings point to decreases in negative mood and anger attacks and positive changes in personality traits after antidepressant treatment. Clinical studies in personality disorder patients have shown some efficacy for serotonergic antidepressants in reducing irritability and impulsive aggression. Experimental work in healthy volunteers has shown both serotonergic and noradrenergic antidepressants to increase assertiveness and affiliative behaviour. Both may therefore decrease aggression through different routes.