Twenty-five managers who reported an average daily caffeine consumption of 575 mg participated in two complex simulations. A double-blind cross-over design was employed to assess the effects of normal caffeine consumption versus caffeine deprivation upon seven validated measures of managerial effectiveness. Data from a Caffeine Withdrawal Questionnaire indicated discomfort upon deprivation. Systolic blood pressure increased during "normal" caffeine consumption levels but fell quickly and remained lower during deprivation. Several measures of managerial performance indicated decreased effectiveness upon caffeine deprivation. In contrast to prior research from simpler task settings, cognitive effectiveness (during complex task performance) was diminished. However, a measure of strategic performance which requires a relatively high level of cognitive effort showed no impact of caffeine deprivation.