The caffeine in coffee, tea and cola can produce addiction similar to that engendered by alcohol, tobacco, heroin and cocaine, researchers from Johns Hopkins University report today.
Although abruptly halting the intake of caffeine has long been known to trigger withdrawal symptoms that include headaches, lethargy and depression, the new report in the Journal of the American Medical Assn. suggests that the drug produces the full range of characteristics associated with classical psychoactive dependence.
Those characteristics include persistent, unsuccessful efforts to reduce consumption, continued use despite medical side effects, tolerance--or the need for ever-higher doses to achieve the same psychological effect--and withdrawal symptoms when use is stopped.
Some evidence suggests that the prevalence of dependence on caffeine is about the same as for alcohol--about 14% of users--according to an editorial by Dr. Richard M. Glass of the association's staff.
The researchers undertook the study "because there are some people who have problems with caffeine use and are distressed by it," said Dr. Eric C. Strain, the Johns Hopkins psychiatrist who co-authored the study. "It is helpful because it shows us that caffeine is a drug like other drugs and in terms of understanding the whole addiction process," he said.
Although caffeine can cause symptoms such as sleeplessness and anxiety, he noted that it has far fewer ill effects than other addictive drugs such as nicotine, alcohol, heroin and cocaine, so that the significance of addiction to it is not yet clear. "This doesn't mean that people have to stop drinking coffee," Strain said.
Nevertheless, the results led Dr. John R. Hughes of the University of Vermont to suggest that "perhaps we should start labeling coffee to indicate its addictive potential. That's something I'd like to know as a consumer."
In a press release distributed by the International Food Information Council, a trade group, Dr. Peter Dews of Harvard Medical School said, "This study . . . adds nothing of relevance to normal people consuming caffeine. The majority of these people (in the study) had a history of serious substance abuse or had mood disorders such as major depression."
Strain conceded that 11 of the 27 participants in the study had previously suffered from substance abuse or mood disorders, but had been in remission for four to eight years before the onset of the study. "They did not have active disorders," he said, and the fact that they had previously had such disorders was not relevant.
Fully 80% of adult Americans consume caffeine regularly, with an average daily dose of about 280 milligrams. (A 5-ounce cup of coffee or tea contains about 100 milligrams of caffeine, while a 12-ounce cola contains about 60. Chocolate drinks and chocolate candy also contain caffeine, but much less.)
Strain and his colleagues ran newspaper advertisements soliciting people who thought they were dependent on caffeine. Telephone interviews of 99 respondents identified 27, ranging in age from 21 to 48, who were willing to visit the laboratory twice, undergo standardized medical and psychiatric interviews and keep a detailed food diary for a week.
Examining the 27 subjects, the team found that 94% displayed withdrawal symptoms when abstinent from caffeine and 94% continued caffeine use despite medical counterindications. Some 81% had made unsuccessful efforts to cut down on caffeine use, while 75% needed increasing amounts. Overall, 16 of the 27 showed all four categories that define classic dependence.
To further explore withdrawal symptoms, 11 of the 16 who were caffeine-dependent (five coffee drinkers, five cola drinkers and one tea drinker) volunteered to undergo two two-day periods in which they consumed a caffeine-free diet. During one two-day period, they were given their normal dose of caffeine in pill form and in the other they were given a placebo.
Eight of the 11 displayed dramatic withdrawal symptoms when they received no caffeine, including impairment in their normal functioning. One of the subjects on placebo sat in her office at work with the lights off and her head down, one man made multiple costly mistakes, and another missed work entirely. One woman canceled her son's birthday party and called her spouse home early because of her inability to care for the children, while another stopped shopping, performing household chores and even such mundane tasks as preparing her child's lunch. Five took aspirin or acetaminophen even though the researchers had asked them not to.
These withdrawal-related behaviors stopped when the subjects resumed caffeine consumption, the researchers said.