According to The Washington Times, a recent study concludes that "a single cup of coffee a day can produce 'caffeine addiction,'" featuring withdrawal symptoms such as headache, drownsiness, difficulty concentrating, irritability, depression, nausea, and muscle aches. In response, the National Coffee Association argues that caffeine is not truly addictive because its users do not develop tolerance, the withdrawal symtoms are not severe enough, and the drug is "still considered safe."
But neither tolerance nor withdrawal is required for addiction--a point the American Psychiatric Association's current definition of "substance dependence" concedes. And the issue of health effects is distinct from the question of how hard a drug is to give up: A person may be very strongly attached to a substance that has a negligible effect on his health.
Such is the case for many regular coffee drinkers, who might have a hard time giving up their habit but don't really want to, since it is not hurting them and does not disrupt their lives. (To the contrary, it probably enhances their productivity and their enjoyment of social situations.) As the lead author of the study notes, caffeine, the world's most popular recreational drug, is "cheap and readily available, so people can maintain their use of caffeine quite easily." If caffeine were illegal, its aficionados would more closely resemble the popular image of drug addicts as desperate, twitchy outlaws.