Continued: NO FLAGGING

Suck down an energy drink and you'll sizzle with newfound energy, ace your next exam and flap through the sky on taurine, ginkgo and guarana-powered wings. At least that's what the makers of energy drinks want us to think. But are those fizzy caffeine- and vitamin-stoked beverages any different from a cup of coffee or can of soda? And could they be harming people who guzzle too many?

Scan the refrigerated section of the corner store. It's overflowing with energy drinks with names such as Inked, Red Bull, Go Fast and Vamp. More than 500 of the slickly packaged drinks were introduced nationwide in 2007, and they're discussed in blogs, reviewed on websites and promoted at sporting events. Buy one and you're buying into a whole hip, young culture.

Credit Austria-based Red Bull for starting the trend in 1987 when it unveiled a carbonated, citrus-flavored drink it claimed could improve performance and concentration. Red Bull sold about 2.5 billion cans worldwide last year.

Sales of energy drinks in the United States hit about $5 billion in 2007, up from $3.5 billion in 2006. Most brands target male teens and people in their 20s, but the market is broadening, according to John Sicher, editor and publisher of Beverage Digest. Consumers are drinking them to study harder, stay up later and party longer.

It's a culture that Seth Juarez, a 26-year-old employee of the Jewelry Channel in Austin, Texas, knows well. He launches his workday with a cup of coffee, then gulps a low-calorie energy drink. He repeats the process as the day wears on.

"Mostly, I drink them for energy," Juarez says. "To be honest, I'm not too keen on the taste. It might be psychological, but [when I drink one] I don't feel tired. That's the key -- if I'm dragging, I drink a Red Bull." He also mixes Red Bull with vodka or Jagermeister when he goes out.

There's an energy drink for almost every personality, and they're eating into the soft drink market. Top sellers include Monster, produced by Hansen Natural Corp.; Rockstar, distributed by Coca-Cola; AMP, from Pepsi, and Full Throttle, produced by Coca-Cola.

Americans have a growing interest in functional beverages that do more than just refresh and taste good, says the beverage industry's Sicher. Energy drinks fulfill that goal. A consumer drinks one and feels a boost of energy almost instantly.

Caffeine + vitamins

Most are packaged in 8- or 12-ounce cans that are taller and thinner than the typical soda can. They come in regular and sugar-free versions, liquid, powder or tablet form, and even 2-ounce noncarbonated shots.

Most people say they drink energy drinks for the kick. These aren't sports drinks like Gatorade, uncarbonated blends of water, sodium and sugars designed to rehydrate sweaty athletes. They're amped up with caffeine -- sometimes two or three times the amount in a cup of coffee -- and loaded with herbs and vitamins.

They're for people who don't like coffee, but still want an energy boost when they're hitting that 3 p.m. lull, says Jim Karwowski of Power Brands, which owns the Energy Drink Reviews website at bandddesigns.com. The site has reviewed about 350 drinks and gets about 5,000 hits a day from readers who gush about their favorites or badmouth ones they don't like. Younger kids see energy drinks as something their parents might disapprove of.

That much ballyhooed boost comes from two things: caffeine and calories.

An 8.3-ounce can of Red Bull contains 76 milligrams of caffeine -- about twice as much as a 12-ounce can of Coke and about the same as an 8-ounce cup of coffee. Under Food and Drug Administration rules, a single serving of a food or drink can contain no more than 65 milligrams of caffeine. But energy drinks aren't regulated by the FDA, so they can -- and do -- contain more, up to 300 milligrams of caffeine per container. It's sometimes hard to tell how much caffeine an energy drink contains, because it can come from several sources. Guarana, for example, a dietary supplement derived from the seed of a South American shrub, contains caffeine, but is usually listed separately on ingredient panels.

Some drinks also contain a slew of ingredients most of us can't pronounce -- such as taurine (an organic acid) and ginkgo biloba (derived from the leaves of a Chinese tree) -- that manufacturers say help sharpen mental focus. But research is slim on those effects. Most of those ingredients, says dietitian Alexa Sparkman of Austin, are superfluous -- our bodies just don't need them. We're better off getting nutrients from foods in which they occur naturally.

That energy boost you think you're getting? Maybe it's all in your head. You may feel more energetic, but many times it's more of an emotional or psychological or placebo effect, Sparkman says. Caffeine, a stimulant that affects the central nervous system, can make you jittery, and that can be interpreted as an energy boost. But there's nothing in the drinks that would truly give you energy that you're not getting from a well-balanced diet.

Watch out for those calories

Most energy drinks contain as much high fructose corn syrup or sugar as regular soda, although low-calorie and low-carbohydrate versions exist. Monster contains about 14 teaspoons of sugar and 200 calories per 16-ounce can.

A calorie is a calorie is a calorie, Sparkman says. If you're drinking these things, you're still adding calories to your diet.

Besides the added calories, the drinks sometimes contain a surprising amount of sodium -- 200 mg or more per serving. At $1.50 to $4 each, they're expensive, too. For some folks, the added vitamins in energy drinks serve as a rationale for a bad habit, Sparkman says.

All that excess has inspired a website, energyfiend.com, where visitors can check the sugar and caffeine content of their favorite drinks. They even can plug in their weight, choose a drink and calculate (in good fun, of course) how many they would have to drink to kill themselves.

But there could be some real cause for concern amid the hype. What are all those energy-boosting ingredients doing to our bodies? A study by Wayne State University in Detroit showed that energy drinks increased blood pressure and heart rate levels in healthy adults who drank two cans a day -- bad news for people with high blood pressure or heart disease. In Chicago, a poison control center handled 265 cases of caffeine abuse involving energy drinks and pills such as NoDoz over a three-year period. The users' average age was under 21.