Kim Leadley didn't think much of her one- or two-a-day Starbucks Grande coffee fix.

But when she tried to go cold turkey to stop the habit, she found herself getting headaches—excruciating headaches, the I-can't-work-think-or-function kind of headaches, she says. Within days, she "fell off the wagon" and resumed the coffee habit.

"The headaches did make me think there was something to be said for caffeine addiction" and withdrawal, said the 41-year-old Cumberland, Maine, resident. She started tapering off her caffeine consumption by mixing decaffeinated and regular coffee. About six months later, she finally kicked the habit for good after getting pregnant in December.

Caffeine, that most-benign seeming drug of choice that keeps so many of us fueled through the day, is now the basis of two official diagnoses in the mental-health bible released in May, with a third brewing for consideration. The latest version of the American Psychiatric Association's Diagnostic and Statistical Manual of Mental Disorders, commonly referred to as DSM-5, includes both caffeine intoxication and withdrawal. These conditions are considered mental disorders when they impair a person's ability to function in daily life.

Caffeine intoxication was included as a diagnosis in the previous version of the manual, known as DSM-IV. But caffeine withdrawal was upgraded in the current manual to a diagnosis from a "research diagnosis" previously, meaning it required further study for inclusion. Also, caffeine use disorder—when a person suffers troubling side effects and isn't able to quit—was added to the current manual as a research diagnosis.