Caffeine habit is tough to kick.

• Position: Chemical Dependency

"People joke about caffeine," says American University, Washington, D.C., psychology professor Laura Juliano, who runs a caffeine treatment study at Johns Hopkins University, Baltimore, Md. "We know how hard it is to get off other drugs, but [it's common to] think, 'Caffeine, yeah, I'll just quit.' And some ... can, [the same as] some people can just quit smoking.... But we've got a group of people who are saying, 'I've been trying to get off this stuff for 12 years, and I can't do it.'"

More than 80% of Americans consume an average of 280 milligrams (roughly three cups of coffee) a day. Undoubtedly, many have quipped about "getting off" caffeine, a description that seems better suited for heroin or cocaine, which share caffeine's psychoactive drug grouping. While caffeine isn't as pernicious as its illegal cousins, there is growing proof that it's a tough habit to kick. Although psychological dependence on caffeine has yet to be widely documented, a physical dependence upon the drug is very evident.

"I can say with confidence that caffeine does cause physical dependence," Juliano maintains. "It has characteristic withdrawal symptoms, which affect people when they abruptly give [it up], and you have a dose dependent relationship." Consuming 100 milligrams a day, or about one cup of coffee, and then stopping consumption is all it takes. The reason so many people overlook these symptoms, and thus their dependence on caffeine, however, is that withdrawal, which...