Popular energy drinks can be found on store shelves everywhere – along with new warnings that they have potentially harmful levels of caffeine.

Sales of energy drinks have boomed to over $5 billion annually as many young Americans pass over a morning cup of coffee for energy drinks, such as Rock Star and Red Bull. "Gives you a little energy boost if you're tired," student Roman Galper said.

However, researchers at John Hopkins University say that some energy drinks have the same caffeine as 14 cans of Coke.

The average 12-ounce cola has 35 milligrams of caffeine, and a 6-ounce coffee contains 80 to 150 milligrams. Energy drinks, which vary in size, can have between 50 and 500 milligrams.

"At the higher level, caffeine is a drug," said Dr. Steven Lamm, an internist at New York University. "It's a stimulant. It's an alerting agent. But it can also induce sweating and hypertension and rapid heart rate."

In rare cases, energy drinks have caused death.

Researchers warn that people who consume caffeine-fueled energy drinks might be more prone to the illicit use of drugs, such as Ritalin, later on.

Because they are marketed as supplements, energy drinks do not have to carry labels revealing how much caffeine is in each can. Experts are calling for better labeling and warnings about the potential risks.

The American Beverage Association, which represents most energy-drink makers, says such labeling is unnecessary.

"Energy drinks have about half the amount of caffeine of a cup of coffee from a coffee house," Susan Neely, with the association, said.

Doctors agree that energy drinks can be safe – in moderation.

Many consumers said new labels and warnings would not make any difference.

"Does it stop smokers from smoking cigarettes when it says it can kill you?" student Damiyr Davis said.