In general, the more caffeine consumed, the more severe withdrawal symptoms are likely to be, but as little as one standard cup of coffee a day can produce caffeine addiction, according to a Johns Hopkins study that reviewed over 170 years of caffeine withdrawal research.

Results of the Johns Hopkins study may result in caffeine withdrawal being included in the next edition of the Diagnostic and Statistical Manual of Mental Disorders, considered the bible of mental disorders, and the diagnosis may be updated in the World Health Organization's International Statistical Classification of Diseases and Related Health Problems.

"Caffeine is the world's most commonly used stimulant, and it's cheap and readily available. So people can maintain their use of caffeine quite easily," says Roland Griffiths, professor of psychiatry and neuroscience at Johns Hopkins. "The latest research demonstrates, however, that when people don't get their usual dose they can suffer a range of withdrawal symptoms, including headache, fatigue, difficulty concentrating. They may even feel like they have the flu with nausea and muscle pain."

Griffiths, and colleague Laura Juliano, Ph.D., of American University published these findings in the October 2004 issue of the journal Psychopharmacology, available online now.

"Despite more than a century and a half of investigation into caffeine withdrawal, doctors and other health professionals have had no scientifically based framework for diagnosing the syndrome," says Griffiths. "Our goal was to critically review the literature regarding caffeine withdrawal to validate the symptoms and signs of illness associated with it, and to determine how often withdrawal produced clinically significant distress."

In their review, the researchers identified 57 experimental studies and nine survey studies on caffeine withdrawal, and examined each to assess the validity of the reported findings.

The researchers identified five clusters of common withdrawal symptoms: headache; fatigue or drowsiness; dysphoric mood including depression and irritability; difficulty concentrating; and flu-like symptoms of nausea, vomiting and muscle pain or stiffness. In experimental studies, 50% of people experienced headache and 13% had clinically significant distress or functional impairment -- for example, severe headache and other symptoms incompatible with working. Typically, onset of symptoms occurred 12 to 24 hours after stopping caffeine, with peak intensity between one and two days, and for a duration of two to nine days. In general, the incidence or severity of symptoms increased with increases in daily dose, but abstinence from doses as low as 100mg per day, or about one small cup of coffee, also produced symptoms.

The research also showed that avoidance of caffeine withdrawal symptoms motivates regular use of caffeine. For example, the satisfying feelings and perceived benefits that many coffee users experience from their morning coffee appear to be a simple reversal of the negative effects of caffeine withdrawal after overnight abstinence.

However, there is good news for those wishing to quit caffeine: A simple, stepwise approach can often eliminate the need for a "fix" without suffering the most severe withdrawal symptoms.

"We teach a systematic method of gradually reducing caffeine consumption over time by substituting decaffeinated or non-caffeinated products. Using such a method allows people to reduce or eliminate withdrawal symptoms," says Griffiths.

According to the report, caffeine is the most widely used behaviorally active drug in the world. In North America, 80% to 90% of adults report regular use of caffeine. Average daily intake of caffeine among caffeine consumers in the U.S. is about 280mg, or about one to two mugs of coffee or three to five bottles of soft drink, with higher intakes estimated in some European countries. In the U.S., coffee and soft drinks are the most common sources of caffeine, with almost half of caffeine consumers ingesting caffeine from multiple sources, including tea.

The study was funded in part by the National Institute on Drug Abuse.