Concern over a controversial beverage concoction of caffeine and booze, that some experts say may not even be legal, could be posing a new health threat for the drinks' biggest fans: college-age people.
Two weeks ago, an athletic, otherwise perfectly healthy 19 year-old man arrived at the emergency room at Temple University Hospital in Philadelphia.
"He had chest pains, he was sweaty, short of breath," said Dr. Robert McNamara, who heads the department of emergency medicine.
The patient was suffering a heart attack.
Tests, however, showed the man had none of the usual signs of an unhealthy heart or arteries.
The symptoms were extremely unusual for such a young person, said McNamara, who added they're typically seen in people who overdose on cocaine or speed. After further questioning, the patient admitted he'd been drinking a new type of beverage, which is growing in popularity, which combines high alcohol content with a large dose of caffeine.
"That was the only explanation we had," for the heart attack, said Dr. McNamara.
The drinks—with names like Joose, Torque and Four Loko-- come in large cans covered with colorful graphics that experts and some students say make the alcoholic beverages hard to tell apart from non-alcoholic ones. The drinks sell for about three dollars each.
Four Loko comes in a 23.5 ounce can that contains 2.82 ounces of alcohol, or 12 percent. Experts say you'd have to drink almost six cans of Bud Light beer, or 67.2 ounces, to get the same amount of alcohol.
The drinks also come with a jolt. The fruit punch-flavored Four Loko has 156 milligrams of caffeine. An eight ounce cup of coffee, by comparison, has about 100 milligrams of caffeine. "This is a dangerous product from what we've seen," Dr. McNamara said. "It doesn't have to be chronic use. I think it could happen to somebody on a first time use."
Dr. McNamara said he had never seen a case like this before. And he said he is now hearing from colleagues about similar cases. A growing number of doctors, lawmakers state and federal officials are warning of potentially serious health problems from the drinks, and some experts argue they are illegal under current federal law.
"It is a quick way to get drunk," said Bruce Goldberger, director of toxicology at the University of Florida College of Medicine. "It is popular among young folks. The marketing and packaging has so much to do with it."
Doctor Mary Claire O'Brien of Wake Forest University led a recent study on the effects of combining alcohol and caffeine. She found that compared to college students who drink only alcohol, students who drink booze mixed with energy drinks are twice as likely to be injured, require medical attention or ride with an intoxicated driver. Those students are also more than twice as likely to take advantage of someone sexually.
Why the difference?
O'Brien said mixing a depressant like alcohol with a caffeine stimulant is akin to stepping on the gas and brake of a car at the same time.
"They can't tell that they're drunk," said O'Brien, an associate professor of emergency medicine and public health. "What this behavior gets is a wide awake drunk."
Drinkers like University of Florida sophomore Daniel Patterson noticed the effects the first time he tried Four Loko.
"I pretty much went into my inebriation without really realizing it," he said in an e-mail. "I was talking a lot, being loud, yet I also felt very alert and sober as if the drink was doing nothing to me."
A website for the manufacturer of Four Loko — Chicago-based Phusion Projects — said the drink is distributed in 47 states.
Phusion says the Philadelphia case is exactly why the company goes to "great lengths" to make sure its drinks are not sold to underage consumers.
"Our cans feature seven different warnings about the product's alcohol content and the necessity of an ID for purchase," the company said in a statement provided to ABC News. "And we're the only manufacturer to prominently place a 'WE ID' message on our can. We also offer free, point-of-sale materials to stores selling our products that reinforce the importance of asking for identification when selling any alcoholic beverage."
The company says it has also rejected social marketing tactics used by some of its competitors.
"There is no company-sponsored "Four Loko" Facebook page or You Tube channel," the statement says.
Fans, however, are using social media to create popular -- if unofficia l— places for Four Loko enthusiasts to spread the word.
One Facebook page bearing the title "four lokos are blackouts in a can and the end of my morals" has more than 71,000 "likes."
As the alcohol-caffeine concoctions -- sometimes dubbed "cocaine in a can" -- are becoming more popular on college campuses, officials are taking notice.
Attorneys general in several states are investigating whether the drinks are being marketed to underage drinkers.
One New Jersey college banned the drinks this month after 23 students were hospitalized with alcohol-related problems. At least some of them reportedly drank Four Loko.
"There's no redeeming social purpose to be served by having the beverage," Ramapao College President Peter Mercer told The Associated Press.
But across Twitter, many people seem to think the ban will only make the drink more popular.
"Four Loko stock is goin (sic) to go thru the roof this weekend," wrote Reacy23.
A Food and Drug Administration spokesman told ABC News that determining whether drinks like Joose and Four Loko are legal is a high priority for the federal agency.
The FDA says food additive regulations currently do not allow mixing caffeine with booze. Drink manufacturers maintain their products contain ingredients that are "generally recognized as safe" but now the FDA wants them to prove it.
Last year the agency sent 27 letters to drink makers seeking more information. 19 companies responded.
"FDA intends to evaluate the information submitted by the manufacturers and other available scientific evidence as soon as possible in order to determine whether caffeine can be safely and lawfully added to alcoholic beverages," spokesman Michael Herndon said in an email.
Herndon said the timing of any FDA decision to regulate the drinks is difficult to predict. Until then, the drinks will continue to be sold. If the agency determines the drinks are illegal or should be regulated, sanctions against the manufacturers could range from a warning letter to having their products seized.
"FDA intends to exercise all options that are appropriate for the product in question," said Herndon.
Dr. O'Brien believes the FDA is dragging its feet by allowing the drinks to stay on store shelves.
"I'm mad as hell," O'Brien said. "These drinks are not safe."
Phusion Projects says it is cooperating with the FDA and maintains its products comply with federal and state laws.
"No one is more upset than we are when our products are abused or used unlawfully. But Four Loko is neither the sole contributor to alcohol abuse, nor will additional restrictions on it solve the problem," said the statement.
Dr. McNamara said his 19 year-old patient will recover, but warns it could have been fatal.
"Seeing this in a young guy kind of raises your eyebrows as to whether these products should be available at all," he said.
ABC's Florinda Ricks and The Associated Press contributed to this story.