CHICAGO — More than 500 new energy drinks launched worldwide this year, and coffee fans are probably too old to understand why.

Energy drinks aren't merely popular with young people. They attract fan mail on their own MySpace pages. They spawn urban legends. They get reviewed by bloggers. And they taste like carbonated cough syrup.

Vying for the dollars of teenagers with promises of weight loss, increased endurance and legal highs, the new products join top-sellers Red Bull, Monster and Rockstar to make up a $3.4 billion-a-year industry that grew by 80 percent last year.

Thirty-one percent of U.S. teenagers say they drink energy drinks, according to Simmons Research. That represents 7.6 million teens, a jump of almost 3 million in three years.

Nutritionists warn that the drinks, laden with caffeine and sugar, can hook kids on an unhealthy jolt-and-crash cycle. The caffeine comes from multiple sources, making it hard to tell how much the drinks contain. Some have B vitamins, which when taken in megadoses can cause rapid heartbeat, and numbness and tingling in the hands and feet.

But the biggest worry is how some teens use the drinks. Some report downing several cans in a row to get a buzz, and a new study found a surprising number of poison-center calls from young people getting sick from too much caffeine.

Danger only adds to the appeal, said Bryan Greenberg, a marketing consultant and an assistant professor of marketing at Elizabethtown College.

"Young people need to break away from the bonds of adults and what society thinks is right," he said. They've grown up watching their parents drink Starbucks coffee, and want their own version. Heart palpitations aren't likely to scare them off.

Most brands target male teens and 20-somethings. Industry leader Red Bull, the first energy drink on the market, is now the "big arena band" of the bunch "teetering on the edge of becoming too big and too corporate," Greenberg said.

Greenberg said the fierce competition among hundreds of new drinks, with Austria-based Red Bull guarding the biggest market share, leads to a "ratcheting up" of taboo names as companies try to break out from the crowd.

Cocaine Energy Drink, which launched in September and now sells in convenience stores and nightclubs in six states, is the latest example, following a twisted logic set by drinks named Pimpjuice and Bawls.

Rumors have swirled around Red Bull for years. Contrary to hearsay, the ingredient taurine (an amino acid important in making bile to aid digestion) is not made from bull urine, and Mateschitz did not learn about Red Bull from rickshaw drivers in Thailand. The urban legends-debunking Web site www.snopes.com has a page devoted to exposing the false claim that Red Bull contains a banned substance linked to brain tumors.

No evidence was ever found that sudden deaths in Ireland and Sweden were caused by people drinking Red Bull. But it's true that the Swedish government studied energy drinks and recommended they not be used to quench thirst or replenish liquid when exercising. And they should not be mixed with alcohol.

Too late. Anheuser-Busch and Miller Brewing now produce several "energy beers" — beer containing caffeine. And Red Bull and vodka — mixed up by bartenders who call it a Friday Flattener or a Dirty Pompadour — has been popular for a decade.

The potential for accidents and alcohol poisoning worries Dr. Sandra Braganza, a pediatrician and nutrition expert at the Children's Hospital at Montefiore in New York. As she prepared to write an article about energy drinks for a pediatrics journal, she was surprised how little published research she could find on them.

"The truth is, we don't know what kind of effects these ingredients can have," Braganza said of taurine, glucuronolactone and guarana. "We have to start doing more studies on this."