The debate over how safe those popular energy drinks are looks to be headed to court, while the Food and Drug Administration investigates how much caffeine is too much caffeine.

The FDA's decision to investigate Monster Energy drinks is based partly on what happened last December when a 14-year-old girl went into a coma after drinking two large cans of Monster Energy. She died a few days later.

In one day, she ingested an amount of caffeine equivalent to 14, 12-ounce cans of soda.

They haven't established a direct link, but what we do know is that toxic levels of caffeine can cause pretty dangerous heart rhythm problems, said Dr. Nieca Goldberg, cardiologist, NYU Medical Center.

If you are very young, very old, have heart conditions, if you take certain medications, you have to be aware. So, you have to look for this information, said Madelyn Fernstrom, Today diet and nutrition editor.

But finding that information is part of the problem.

Energy drinks aren't regulated and aren't required to post caffeine content or warning labels.

Still, the FDA is looking at five such deaths over the last three years, all involving Monster Energy.

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