Antagonistic effects of caffeine and yohimbine in animal tests of anxiety.

The effect of a combination of caffeine and yohimbine was investigated in the social interaction, elevated plus-maze and punished-drinking tests of anxiety. Caffeine (40 mg/kg i.p.) had anxiogenic-like effects in the social interaction and plus-maze tests. Yohimbine (2.5 mg/kg i.p.) was anxiogenic-like in the plus-maze and displayed anticonflict activity. Unexpectedly, caffeine and yohimbine antagonized each others' effects in the social interaction and elevated plus-maze tests.