Bar-goers mix them with vodka to stay up and party longer. Students drink them to help pull all-night study sessions. And some athletes down them to boost performance.
So-called energy drinks _ a new breed of concoctions with stiff doses of caffeine, sugar and a mixture of herbs and other substances _ are fast becoming the younger generation's pick-me-up of choice.
That's raising the concern of some doctors and nutritionists, despite assurances from the drink-makers, who say the products are harmless so long as people who use them also stay hydrated. Water is an issue because caffeine, like alcohol, is a diuretic that promotes fluid loss.
``When it's all said and done, most energy drinks are caffeine and sugar, as are most soda pops,'' says Jim Heidenreich, vice president of marketing for Colorado-based EAS Inc., which began marketing Piranha brand energy drinks on the extreme sports and college scenes this year.
But some health experts aren't convinced energy drinks are safe. They say young people already consume unhealthy amounts of caffeine and don't need a product that raises that intake. They also believe the penchant for mixing a strong stimulant with alcohol _ a practice Piranha warns against on its label _ is a disaster waiting to happen.
Officials in Canada, France, Norway and Denmark have yet to approve many energy drinks, including Austria's Red Bull, which accounts for more than half of booming energy drink sales in this country.
And last summer, Sweden's National Food Administration began advising people not to consume Red Bull with alcohol, or as a thirst-quencher. The recommendation came after a young woman who had consumed alcohol with the popular product died, apparently of dehydration. Two other deaths are also under investigation.
Emmy Cortes, a spokeswoman for Red Bull North America, says Swedish officials have yet to prove a link between the deaths and her company's drink. She also says Red Bull does not promote mixing its product with alcohol, though the company only warns against doing so in Austria, and commonly sells its product by the caseload to bars and nightclubs.
``We know it happens,'' she says, noting that few would question cola-makers about the popularity of mixing their product with rum. ``What's going to happen is going to happen.''
Dr. Michael Hirt, a California physician, is more worried about the smaller number of drinks that contain the drug ephedrine, a stimulant occasionally used in energy drinks that is also included in decongestants. Combined with caffeine, he says, ephedrine has been proven to cause deadly heart problems.
High school officials in Burbank, Calif., banned energy drinks last year when two student athletes who had consumed drinks with ephedrine fainted.
A more common energy drink ingredient is taurine, an amino acid which occurs naturally in other foods, though in significantly smaller quantities.
Hirt estimates that one can of Red Bull has about as much taurine in it as 500 glasses of red wine _ a level he says is theoretically supposed to boost the effects of the drinks' stimulants but has not been studied for long-term effects.
Many drinks also contain guarana or extract from its seeds, yet another source of caffeine.
``It just becomes more of a witches brew. You're playing with things that we don't really understand and the long-term consequences are unclear,'' says Hirt, medical director at the Center for Integrative Medicine at the Encino-Tarzana Regional Medical Center in Encino, Calif.
Emily Hunter, an Emory University sophomore, first discovered energy drinks while on a study trip to Sweden. Now, she says, they're all the rage on her Georgia campus. She and students elsewhere say product giveaways and promotions at bars near their campuses are common.
``They like the taste. They like the kick,'' Hunter says of her peers. ``They don't know about any of the negative side effects.''
Already, sales in this country have more than doubled since last year, according to the Beverage Marketing Corp. _ from $130 million in wholesale sales to a projected $275 million this year. Such figures helped entice such beverage giants as Coca-Cola and Anheuser-Busch to introduce their own products _ called KMX and 180.
Julie Woods, an Australian nutritionist who heads a food regulation advisory group for her country's Public Health Association, says such growth will only heighten the debate.
Earlier this year, Australia began requiring a warning label on energy drinks: ``This food is not recommended for children, pregnant or lactating women and individuals sensitive to caffeine.''
Woods wants to see even more restrictions, such as a ban on sales to those younger than 18. But Red Bull's Cortes says that would only make her company's product more enticing to minors.
David Shattuck, a self-proclaimed energy drink lover and writer for the student newspaper at Oklahoma State University, thinks he should be trusted to know what he's drinking.
``Go out and buy as much as possible,'' he urged his peers in a column, ``before some genius legislator or school official bans the stuff indefinitely.''