Scientists at Johns Hopkins University (Baltimore, MD), after decades of researching the effects of caffeine, believe caffeinated energy drinks should list caffeine doses on a label and warn consumers of potential health risks of caffeine intoxication, Some energy drinks contain the equivalent of 14 cans of Coca-Cola. Symptoms of caffeine intoxication include nervousness, anxiety, restlessness, insomnia, gastrointestinal upset, tremors and rapid heartbeat. A regular 12-ounce cola drink has about 35 milligrams of caffeine. Energy drinks, on the other hand, contain anywhere from 50 to more than 500 milligrams.
Source: Drug and Alcohol Dependence, MuscleMag