Starting with Red Bull's debut in 1997, the energy drink phenomenon exploded with competitors like Monster, Rockstar and 5-Hour Energy shots now in nearly any place with retail shelves and beverage cases.
The drinks promise to be a quick antidote to fatigue with a jolt of mental edge. Popular on college campuses and among teens, energy drinks are heavily marketed amid the aura of extreme sports and celebrities. Billions of cans are sold each year.
Lately, though, energy drinks have come under scrutiny with headlines such as this one: "Can Energy Drinks Kill?"
Last November, the Food and Drug Administration announced that it is investigating reports that some energy drinks possibly sent people to emergency rooms or even caused deaths.
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Through its adverse event reporting system, the FDA has been notified of illnesses and deaths suspected of being linked to Monster, 5-Hour Energy Shots and Rockstar Energy.
The reports go back as far as 2004 but the FDA cautioned they are alerts only. The system signals when investigations may be needed; investigators must determine whether a product or something else was the underlying cause of harm.
Most energy drinks are sold as supplements and not food. Listed on labels are ingredients like the amino acid taurine, B vitamins and herbal supplements like ginseng and ginkgo. There are lots of sugars and sweeteners, sometimes surpassing amounts in a regular Coke.
And the key ingredient: caffeine.
The caffeine is really what's behind an energy drink's kick, said dietitian Christine Gerbstadt, a spokeswoman for the Academy of Nutrition and Dietetics.
Although many energy drinks don't contain any more caffeine than a cup of coffee, "it's the quantity people are drinking. People drink these things like crazy," she said.
Too much caffeine can cause the jitters and anxiety. It can keep people up at night, raise blood pressure levels and make the heart race.
Some energy drinks have labels that caution the beverages aren't recommended for children, pregnant women and people sensitive to caffeine. The Amazon site selling 12-packs of Monster X-presso has this disclaimer: Consume responsibly, max 1 can every 4 hours, with limit 3 cans per day.
Added B vitamins tend to be at least 100 percent of recommended daily amounts but also can spike much higher.
On the bottle of 5-Hour Energy is a warning that the product's high amount of niacin may cause a bloom of itchy red skin called the "niacin flush."
A niacin flush isn't harmful but can be annoying for some people, said Gerbstadt. Meanwhile, a portion of those B vitamins will be flushed down the toilet, she said. The body excretes excess amounts.
Who shouldn't be consuming energy drinks are children, according to health experts.
The American Academy of Pediatrics issued a report in 2011 that said energy drinks are never appropriate for children and teens. Caffeine has been linked to harmful effects on developing cardiovascular and neurological systems.
Young athletes also confuse energy drinks with sports drinks that are meant to rehydrate, said the report. Energy drinks are in a different beverage category and are dehydrating due to their caffeine content.
"Imagine that an energy drink is equivalent to two to four cups of coffee. You wouldn't have an 11-year-old drinking a cup of coffee," said cardiologist Mohammed Saghir of the Bradenton Cardiology Center.
People with cardiovascular problems also should be wary. Very high doses of caffeine could contribute to arrhythmia when the heart beats rapidly and erratically, said Saghir.
Last December, Consumer Reports published lab results for the amount of caffeine in 27 popular energy drinks and shots.
Examples: the 6.8-ounce serving size of Monster X-presso contains 221 milligrams of caffeine. A shot of 5-hour Energy Extra Strength, which comes in 1.9 ounce bottles, contains 242 milligrams.
By comparison, an 8-ounce cup of coffee has about 100 milligrams; a 16-ounceStarbucks Grande has about 330 milligrams, according to the Consumer Reports study.
As with many things, moderation is recommended as the way to go in drinking energy beverages. That means don't guzzle.
"They aren't the drinks I prefer, but I don't know if that means you can never have them," said Saghir.
"Once in awhile may beOK but don't make it a habit."
The amount of caffeine equivalent to two 8-ounce cups of coffee is OK according to the American Heart Association, said Gerbstadt.
Be sure to include the caffeine in tea, soda and chocolate when adding up the daily total.
Susan Hemmingway, Herald health correspondent, can be reached at firstname.lastname@example.org.