Anxiety and muscle tension as consequences of caffeine withdrawal.

Regular consumers of caffeine had higher muscle tension after three or more hours of abstinence than low caffeine consumers. This difference was absent after double-blind administration of caffeine citrate or placebo. In a discriminative reaction time test, caffeine treatment improved performance. Among subjects receiving placebo, anxiety was highly correlated with prior caffeine use, suggesting that even a brief abstinence may produce anxiety in the regular user.