'Energy drinks' like Red Bull have become popular mixers at bars, but some experts worry about the health effects of these largely unregulated drinks even when alcohol isn't added to the mix.

The New York Times reported June 19 that drinks like Red Bull, EndoRush, and Vitamin Water often contain megadoses of caffeine and other stimulants, vitamin B12, brain-stimulating nootropics, amino acids, and more. In 2005 alone, $1.83-billion worth of these drinks were sold, many to consumers attracted by claims of improved physical performance.

"There is no getting away from these things," said David Ellis, a sports nutrition expert. "They are absolutely in every locker room."

But Ellis and others worry about combining energy drinks with exercise. Experts say it is important for athletes to replace water and electrolytes, but the stimulants in energy drinks -- including guarana and bitter orange, a legal substitute for banned ephedra -- can cause increased heartbeat and other problems. Also, said Ellis, "They help blunt your perception of pain. That might be good in the short term, but the bad news is if you don't feel the fatigue in a hot, humid environment, your body won't make you slow down to minimize overheating. Exertional heatstroke is a real possibility."

Ellis also said that heavy users of energy drinks could fall into an addictive pattern. "The question becomes how do you get to sleep at night?" he said. "Athletes who use too much are still gnashing their teeth with their hair standing up at 1 or 2 in the morning. A lot of times, they'll use alcohol to wind down. The stimulant-alcohol cycle is the quickest way to end an athletic career."