Effects of low doses of caffeine on aggressive behavior of male rats

To date, the effect of low doses of caffeine on aggression has not been sys tematically examined. Doses of caffeine greater than 30 mg/kg appear to red uce social interaction and aggression in all species studied. In a double b lind study of the effects of low doses of caffeine on aggression, rats were housed four per cage, and aggressive behavior against an intruder was reco rded during baseline and following administration of 2.5, 5, 10, and 20 mg/ kg caffeine. Aggressive behavior was significantly increased following admi nistration of the higher doses of caffeine. Doses of 5, 10, and 20 mg/kg ca ffeine all were effective in increasing pushing behavior, whereas doses of 5 and 10 mg/kg were most effective in increasing boxing behavior, and a dos e of 10 mg/kg was significantly more effective than other doses in increasi ng chasing and roll-tumble-bite behaviors. Based on these results and other published reports, the inverted-U shaped dose-dependent effect of caffeine on aggression appears to apply, with aggressive behavior being most elevat ed following doses of 5-20 mg/kg caffeine, less elevated following 2.5 mg/k g or 30 mg/kg, and significantly reduced with doses above 40 mg/kg and at d oses below 2.5 mg/kg.