After reports that highly caffeinated Monster energy drinks may have been linked to five deaths in the past three years, doctors are expressing concern about the large amounts of caffeine in these types of beverages.

The family of a 14-year-old Maryland girl who died from an irregular heart rhythm after drinking Monster energy drinks has filed a lawsuit against Monster Beverage Co., of Corona, Calif. All five cases have been filed as "adverse event reports" with the U.S. Food and Drug Administration.

The effects of large amounts of caffeine are underappreciated, said Dr. Suzanne Steinbaum, a preventive cardiologist at Lenox Hill Hospital in New York City. "People may think that these energy drinks are healthy by the way they're marketed," she said.

There are, however, 240 milligrams of caffeine in some of these drinks, Steinbaum said. "That's seven times the amount of caffeine in a can of soda," she added.

Caffeine can increase the heart rate tremendously and drive blood pressure up, Steinbaum explained. "In anyone who has any underlying heart condition, these two effects can be deadly," she said. "Know what you're drinking before you drink it."

The FDA can't say definitively that the deaths were the result of the drinks, but an agency spokeswoman said the events are concerning.

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