HAGERSTOWN, Md. >> The highly caffeinated Monster Energy Drink is being linked to five deaths and one non-fatal heart attack, according to reports that the U.S. Food and Drug Administration is investigating.

The reports claim that people had adverse reactions after they consumed Monster Energy Drink, which comes in 24-ounce cans and contain 240 milligrams of caffeine, or seven times the amount of the caffeine in a 12-ounce cola.

Although the FDA is investigating the allegations, which date back to 2004, the agency said the reports don’t necessarily prove that the drinks caused the deaths or injuries.

“As with any reports of a death or injury the agency receives, we take them very seriously and investigate diligently,” Shelly Burgess said in a statement.

Monster Beverage Corp., which makes the energy drinks, did not immediately respond to calls seeking comment on Monday, but the company has denied that its products caused any deaths. The Corona, Calif.-based company said last week that “Monster is unaware of any fatality anywhere that has been caused by its drinks.”

Monster’s shares plunged $7.59, or 14.2 percent, to close at $45.73 in trading on Monday.

News of the FDA’s investigation follows a filing last week of a wrongful death suit in Riverside, Calif., by the parents of a 14-year-old Hagerstown girl who died after drinking two, 24-ounce Monster Beverage Corp. drinks in 24 hours.

An autopsy concluded that Anais Fournier died of cardiac arrhythmia due to caffeine toxicity. The medical examiner also found that she had an inherited disorder that can weaken blood vessels.

Fournier’s parents Wendy Crossland and Richard Fournier claim Monster failed to warn about the risks of drinking its products.

The company touts Monster Energy Drink on its website as a “killer energy brew” and “the meanest energy supplement on the planet.” The cans bear labels stating that the drinks are not recommended for children and people who are sensitive to caffeine.

Energy drinks are a tiny part of the carbonated soft drink market, representing about 3 percent of sales volume, according to a recent report by industry tracker Beverage Digest. Last year, sales volume for energy drinks rose by nearly 17 percent.

The increased sales have brought heightened scrutiny from state and federal authorities.

In August, New York state Attorney General Eric Schneiderman issued subpoenas to energy drink makers, including Monster, as part of the state’s investigation of the industry. In September, Senators Dick Durbin, D-Ill., and Richard Blumenthal, D-Conn., asked the FDA to take another look at the effect that caffeine and other ingredients in energy drinks have on children and adolescents.

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Matthew Perrone reported from Washington.