Effects of a low dose of caffeine given in different drinks on mood and performance

An experiment was carried out to examine the effects of 40 mg of caffeine given in different drinks (coffee, water, tea, cola) on mood and performance. One hundred and forty-four volunteers were randomly assigned to one of the groups formed by combining the caffeine/placebo and drinks conditions. Following a baseline session measuring mood and different aspects of performance, the volunteers were given their drink:and then carried out another test session Ih later. Administration of the caffeine/placebo was double-blind. The. results showed that those given caffeine reported greater alertness and anxiety at the end of the test session, as-well as improved performance on choice reaction time tasks involving focused attention and categoric search, a semantic memory task and a delayed recognition memory task. The effect of the caffeine was not modified by the nature of the drink in which it was given. Overall, these results show that a dose of caffeine typical of the level found in commercial products can improve alertness and performance efficiency. Copyright (C) 1999 John Wiley & Sons, Ltd.