You've seen them in the grocery store refrigerated coolers, with fancy names, like Red Bull, Monster, Full Throttle, and Rockstar. They're the so-called "energy drinks" that come loaded with caffeine, sugar, vitamins, minerals, and other ingredients. But are they really good for you? Johns Hopkins reviews the data.

The popular high-caffeine, high-sugar beverages, typically sold in 8.3 oz aluminum cans (two-thirds the size of a standard size of Coca-Cola) contain about seven teaspoons of sugar and as much as two to four times the amount of caffeine (9 milligrams per fluid ounce) as Coke.

Caffeine is a drug and should be treated with caution. Some people are now suggesting that warning labels be placed on energy drink cans because of their high caffeine levels and their potential to raise blood pressure. Elevations in blood pressure were the point of small study presented at a recent American Heart Association meeting.

While the increases didn't reach dangerous levels in the healthy volunteers, the increases in blood pressure and heart rate could prove to be clinically significant in patients with heart disease or in those who consume energy drinks often, said James Kalus, Pharm.D., senior manager of Patient Care Services at Henry Ford Hospital in Detroit, Michigan, who led the study. "Individuals with high blood pressure and heart disease should be advised to avoid these drinks," he said.

Most energy drinks contain high levels of caffeine and taurine, an amino acid also found in protein-containing foods such as meats and fish. Both have been shown in some studies to effect heart function and blood pressure. In contrast, "sports drinks" like Gatorade and POWERade are simply mixtures of water, sugars, minerals, and salts, without chemicals aimed at increasing "energy" or alertness.

In Dr. Kalus' study, blood pressure and heart rate levels increased in healthy adults who drank two cans a day of a popular energy drink. According to Dr. Kalus, these changes occurred while the participants were sitting in chairs watching movies. "The increases in heart rate and blood pressure weren't enough for something to happen acutely," he said, "but a person on hypertension medication or who has cardiovascular disease may not respond as well. While energy drinks increase concentration and wakefulness, people with risk factors for heart disease could have a bad reaction. The subjects in this study were healthy, with low blood pressure."

Dr. Kalus feels that the increases in blood pressure and heart rate may be due to the caffeine and taurine in the drinks. The energy drink used in the study had as much caffeine as one to two cups of coffee, but some of the other energy drinks available contain much higher levels of caffeine.

Bottom line: "Energy drinks could affect some individuals if they didn't know they had a blood pressure problem in the first place," he said. "The study raises some concerns." Until further study, Dr. Kalus said people with high blood pressure or heart disease should steer clear of energy drinks because they could affect blood pressure and may even alter the effectiveness of hypertension medications.