Caffeine antagonizes diazepam effects in man.

In a double-blind, placebo-controlled study on parallel groups of medical students diazepam 10 mg impaired cognitive skills and caused muscle relaxation. A 250 mg dose of caffeine given in decaffeinated coffee counteracted these better than a 500 mg dose. Subjectively, diazepam exerted a calming effect which was counteracted by caffeine at either at either dose levels.