Caffeine is unquestionably the most widely used mood-altering drug in the world.
DSM-IV also includes caffeine withdrawal syndrome as a diagnosis worthy of further study. Although people often joke about being addicted to caffeine, a provocative and interesting question is whether caffeine should be considered a drug of dependence. The ease with which we can answer this question depends on how dependence is defined. Physical dependence is manifested by the presence of withdrawal symptoms that emerge upon termination of repeated caffeine administration. Physical dependence on caffeine has been clearly demonstrated in human and animal studies.