When pop princess Britney Spears needs a pick-me-up, she turns to a popular energy drink for a quick boost.
Red Bull mixed with apple juice, she has said, "really pumps me up."
Highly caffeinated energy drinks - such as Red Bull, Go-Fast!
and Monster - market themselves as sources of increased energy and concentration.
"In the United States, these energy drinks have not had any warnings.
In Europe, it's been more cautionary," says Karam-Hage, medical director of the Chelsea-Arbor Treatment Center, a joint program of the U-M Health System and Chelsea Community Hospital.
The energy drinks typically contain sugar, caffeine (often 80 mg per can, about the same as a cup of coffee), and taurine, a sulfur-containing amino acid.
Some countries have raised concerns about the amount of caffeine in the drinks and the uncertain health effects of taurine.
While Karam-Hage stops short of saying people never should consume energy drinks, he says that mixing them with alcohol is dangerous and should be avoided.
"The best analogy I can come up with is it's the same as driving a car, putting one foot on the gas and one foot on the brakes," he says of combining the stimulants in caffeine and the intoxicating effects of alcohol.
Mixing alcohol and caffeine is nothing new - think of the people who try to sober up by drinking coffee after a night at the bar - but Karam-Hage says the belief that caffeine makes someone alert after drinking alcohol is a myth.
When people consume these beverages before intensive exercise, he says, they should be aware of the effects the drinks have on people's bodies.