Caffeine is known to increase arousal, attention, and information processing-all factors implicated in facilitating persuasion. In a standard attitude-change paradigm, participants consumed an orange-juice drink that either contained caffeine (3.5 mg/kg body weight) or did not (placebo) prior to reading a counterattitudinal communication (anti-voluntary euthanasia). Participants then completed a thought-listing task and a number of attitude scales. The first experiment showed that those who consumed caffeine showed greater agreement with the communication (direct attitude: voluntary euthanasia) and on an issue related to, hut not contained in, the communication (indirect attitude: abortion). The order in which direct and indirect attitudes were measured did not affect the results. A second experiment manipulated the quality of thc arguments in the message (strong vs. weak) to determine whether systematic processing had occurred. There was evidence that systematic processing occurred in both drink conditions, but was greater for those who had consumed catkine. In both experiments, the amount of message-congruent thinking mediated persuasion. These results show that caffeine can increase the extent to which people systematically process and arc influenced by a persuasive communication.This study reports one of the first attempts to explore the effects of caffeine consumption on persuasion . Caffeine (1,3,7-trirnethylxanthine) is a constituent of coffee, tea, cola, and energy drinks and is the most popular and frequently consumed psychoactive substance in the world (James, 1997). Barone and Roberts (1984) and James (1991) indicated that most (over 80%) American adults are moderate caffeine users, consuming approximately 200 mg/day. Similar levels of consumption (220 mg/day) have been reported in the United Kingdom (Brice & Smith, 2002b). The bulk of this caffeine intake is from drinking coffee, although it has been reported that teenagers from the United Kingdom are drinking more cola soft drinks (Jarvis, 1993), and Australian teenagers are drinking large quantities of energy drinks ("Energy drinks," 2001).