Perhaps more troubling, Goldberger said, is that there is little scientific research on how high intakes of caffeine affect adolescents over the long term. Caffeine is difficult to abuse; unpleasant side effects appear even at modest doses, and toxicity occurs only at very high doses. Those who overconsume it are usually teenagers or young adults.
"There's an American subculture out there that loves the idea of being wired," said James Lane, professor of medical psychology at Duke University. "But caffeine produces real psychological and physiological dependence."
A recent survey by researchers at Northwestern University found that an overdose of caffeine supplements triggered more than 250 reports to the Illinois Poison Control Center over a three-year period. The average age of those affected was 21.
At an emergency room in Berkeley, California, Guy Shochat last year treated an 18-year-old who had arrived in an ambulance with sudden heart arrhythmia. The teenager had been drinking eight 16-ounce cans of Rockstar every evening to stay awake for his night job.
"He was totally clueless that there might be something wrong with drinking so much of this stuff," said Shochat, an assistant clinical professor of emergency medicine at the University of California, San Francisco.
The American College of Sports Medicine has warned high school athletes away from energy drinks because the caffeine in them may cause dehydration. High schools in Fairfax County, Virginia, this year removed energy drinks from its vending machines after student athletes complained of headaches and nausea after drinking them at practice.
Energy drinks may be a worry at bars and clubs, too, where certain brands are used as mixers. In a recent Brazilian study, 26 men were evaluated as they downed an energy drink and alcohol, separately and in combination. Consumption of the beverages together did not diminish the men's intoxication, as demonstrated on objective tests.
But the combination did reduce the men's ability to perceive their own inebriation, the researchers found, leading the subjects to believe they were more in control than they were. By masking the depressant effects of alcohol, the scientists concluded, energy drinks may have made it more likely that the users drank to excess.
Ordinary use of caffeine may be addictive, experts say, but it is usually benign. Still, there is strong evidence that in a hectic world, this kind of "energy" isn't part of the solution — it's part of the problem.
The grogginess that plagues so many people in the morning and during the day can be a symptom of caffeine withdrawal, according to Lane. Far from being revitalizing, another shot merely sates the user's addiction for a while.
"Caffeine's effect at high doses is like having a chronic anxiety condition," Lane said. "It exaggerates the perception of stress and the body's response to it, and I think it could be contributing to the stress we all experience in daily life."
But if Kirby's reported sales of Cocaine are any measure, the country's jittery romance with caffeine is intact. He said more than 200,000 additional cases of the drink have been ordered and are in production.
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