Caffeine alters mood and behavior, and it can also result in physical dependence, says Roland Griffiths, a professor in the departments of psychiatry and neuroscience at the Johns Hopkins School of Medicine. "People are hesitant to think of it as a drug of addiction because it doesn't have a lot of the health and adverse social consequences associated with our classic drugs of addiction, yet the basic mechanisms by which it hooks people are very much like our classic drugs of addiction," he says.
Most people experience mild to modest withdrawal, Griffiths says, which is relieved by drinking coffee in the morning after abstaining from it overnight. Many people say, "'I really don't get going until I have coffee, [and] then I feel great.' What they're not recognizing is that if they didn't consume coffee [at all], they would wake up feeling great," Griffiths says.
Here are some of the signs of caffeine withdrawal, which typically appear 12 to 24 hours after abstaining from coffee.