Monster Beverage has been sued by the family of a 14-year-old girl who died after she had just two cans of the energy drink.
The Food and Drug Administration announced today it was investigating reports of five deaths associated with the drink and one non-fatal heart attack, prompting the company's shares to fall 14 per cent.
Anais Fournier, died on December 23, 2011 from a heart attack brought on by 'caffeine toxicity' after drinking two 24-ounce Monster cans within 24 hours.
The FDA reported 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.
The wrongful death suit, filed in California Superior Court in Riverside, said that after drinking two 24-ounce cans of Monster Energy on consecutive days, Anais went into cardiac arrest.
An autopsy revealed the teenager, from Hagerstown, Maryland, died of cardiac arrhythmia due to caffeine toxicity that impeded her heart's ability to pump blood.
The medical examiner also found that she had an inherited disorder that can weaken blood vessels.
Miss Fournier's parents Wendy Crossland and Richard Fournier claim Monster failed to warn about the risks of drinking its products.
Ms Crossland told the Record Herald: 'I was shocked to learn the FDA can regulate caffeine in a can of soda, but not these huge energy drinks.
'With their bright colors and names like Monster, Rockstar, and Full Throttle, these drinks are targeting teenagers with no oversight or accountability. These drinks are death traps for young, developing girls and boys, like my daughter, Anais.'
Monster is the leading U.S. energy drink by volume with nearly 39 per cent of the market, but Austria's Red Bull has the highest share by revenue due to its premium price.
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.
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 said it does not believe its drinks are 'in any way responsible' for Miss Fournier's death.
'Monster is unaware of any fatality anywhere that has been caused by its drinks,' the company said in a statement. It said it intends to vigorously defend itself in the suit.
Monster's shares plunged $7.59, or 14.2 percent, to close at $45.73 in trading on Monday.
Energy drinks are a tiny part of the carbonated soft drink market, representing about 3 per cent of sales volume, according to a recent report by industry tracker Beverage Digest. Last year, sales volume for energy drinks rose by nearly 17 per cent.
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.