This chapter summarizes the data available concerning the syndrome of intoxication and considers the clinical importance of the phenomenon. Medical case reports of caffeine toxicity, referred to as the “syndrome of coffee”, appeared intermittently as early as the beginning of the 20th century. No sound epidemiologic data on the prevalence of caffeine abuse and intoxication are available. It has been suggested that the use of caffeine is influenced by the reinforcing properties of taste, hedonic psychoactive effects, and the desire to avoid withdrawal. Caffeine is a naturally occurring xanthine derivative and is considerably more potent than another commonly known methylxanthine, theophylline. Caffeinism can mimic or aggravate a number of physical and psychiatric disorders. The observation of elevated anxiety symptoms among consumers of large amounts of caffeine may be expected because caffeine has pharmacological effects of central nervous stimulation and also increases catecholamine output as discussed previously.