Most industry-leading energy drinks such as Red Bull, Monster, and Rockstar contain between 105 and 120 milligrams of caffeine per 12-ounce serving. It's less caffeine per ounce than coffee and some teas, but many energy drinks add energy-touting cocktails of herbal extracts and dietary supplements ranging from ginseng and ephedrine (an herbal extract) to taurine (an amino) and horny goat weed.
"It's not meant to be a health drink," says Chris Kennedy of Wet Planet Beverages, the maker of Jolt Cola. Jolt was introduced in 1985 as one of the first "caffeine enhanced" soft drinks. "We're not recommending 19 Jolts," Mr. Kennedy says. "What we're saying is one or two ... or three." Three would be the equivalent of 216 milligrams of caffeine.
What is driving the sales of energy drinks? They are profitable and aggressively marketed, and consumers like their "energy function," says John Sicher, publisher of the trade publication Beverage Digest. "It's one thing to drink a beverage with vitamins and calcium. It may be good for you, but you don't feel it," he says. "[With energy drinks], there's an immediate gratification because you can feel it."
People don't drink them for the taste, says Jon Marlow, manager of the Toledo Lounge in Washington, D.C. The most popular energy-drink mix his bar serves, a Red Bull-Vodka, is $9. "People do it because they can order something that's got caffeine that isn't hot like coffee."
There are about 130 energy drinks available in the US, says BevNET's Mr. Craven. Most are sold by the can from convenience-store coolers for about $2 each, but cost isn't slowing consumption.
Red Bull, headquartered in Austria, sold about 1 billion cans worldwide last year. That got the attention of Coca-Cola and Pepsi, both of which are eagerly joining the energy drink market. Since last year, the beverage giants have been pulling less profitable soft drinks off store shelves to make room for more caffeine-potent options.
And what about all that caffeine?
"Caffeine isn't innocuous," says Roland Griffiths of the department of neuroscience at Johns Hopkins University in Baltimore. "It's important to recognize that it's a drug. But there's no hard-and-fast rule for how much is problematic."