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Ian Keith, left, gave up energy drinks but is back to one per day. Nancy McAdam tried an energy drink once, saw her hands shaking, and stopped. Both are Portland High athletes.

First came the headaches. Then the sleepless nights.

Ian Keith, a junior wrestler and rugby player at Portland High, was trying to stop using energy drinks. He had been drinking them since eighth grade.

"I started with Monster," he said. "Then I started drinking them like candy."

But the withdrawal symptoms made it hard to kick. Four months after he stopped, he started drinking them again.

"One a day," he said.

Energy drinks such as Red Bull, Monster, Amp Energy, Rockstar and 5-Hour Energy have become a significant part of the athletic landscape – much to the chagrin of trainers and coaches who try to steer teenagers away from them.

Trainers preach about healthful diets, with proper doses of fruits and vegetables, and the importance of hydration with water.

Some coaches even ban their players from drinking them during the season. But they also know how difficult it is to dissuade teens from trying energy drinks when they are promoted by athletes such as Kevin Youkilis (SlumpBuster), Reggie Bush (Red Bull) and Dale Earnhardt Jr. (Amp).

"Kids see that stuff," said Greg Paradis, the Thornton Academy baseball coach. "When major leaguers act a certain way, you know our kids are going to act that way, too."

And what they see may not necessarily be what they get.

Heath Pierce, a clinical instructor at the University of New England, said if athletes are looking to improve, energy drinks are not the route to take.

"As an athlete, you know you have to be hydrated, you have to keep your body temperature regulated," he said. "An energy drink can dehydrate you, their carbonation can cause you to have gastrointestinal problems, and they can contain too much glucose (sugar), which will slow your body down metabolically.

"You're essentially fighting against what you want to do."

Pierce, whose expertise is strength and conditioning, and who has followed extensive research on supplements (which energy drinks are considered), said it's important to know the ingredients.

There's a significant difference, he said, between energy drinks, which contain large doses of caffeine and sugar and are often carbonated, and sports drinks such as Gatorade, which include carbohydrates, electrolytes and aren't carbonated.

"Energy drinks are very much like a soft drink or soda," said Pierce. "What a true sports drink should have, and when you look at what an energy drink actually has, they are completely opposite."

No one disputes that energy drinks provide a burst of energy. But ingredients in some – such as taurine, an amino acid originally isolated from ox bile, and guarana, a natural compound herb that contains caffeine – are on the NCAA's list of banned substances.

Energy drinks tend to have high doses of caffeine – anywhere between 80 and 500 milligrams in a 12-ounce can. For example, Red Bull, sold in an 8.2-ounce can, has 80 milligrams. A 12-ounce can of Coke Classic has 34.

Trainers worry that the high caffeine content will exert more stress on the heart, which is already beating faster because of physical activity. "You're just putting extra demands on your heart," said Audrey McKenzie, the Portland High trainer.

Too much caffeine also could lead to dehydration because it causes frequent urination.

The high dosage of sugar is an issue as well. Sports drinks tend to have between 6 percent and 8 percent glucose. Energy drinks have between 10 percent and 20 percent.

"That 6 to 8 percent is important," said UNE's Pierce. "Once you're over that amount of sugar in your system, it can cause problems."

Too much sugar causes the body to absorb water more slowly, which can lead to dehydration and potential liver problems. The lack of electrolytes in energy drinks is also a concern. The body loses electrolytes – which carry electrical impulses through your body...