The United States Food and Drug Administration is investigating five deaths and a heart attack for possible links to consumption of a brand of energy drink.
The FDA says the fact it is investigating Monster Energy drinks does not prove the cause, but it is taking the reports seriously.
The company that produces the drink, which is available in New Zealand, is being sued by the family of 14-year-old Anais Fournier, who say she died after drinking two cans of Monster Energy over a 24-hour period, AFP reports.
Her parents accused the company, Monster Beverage Corporation, of not warning consumers of the potential dangers of its product.
According to the complaint, the two cans of energy drink that the girl consumed contained about 480 milligrams of caffeine - the equivalent of 14 Coca-Colas.
The company has denied any responsibility for the death.
"Monster does not believe that its products are in any way responsible for the death of Ms Fournier and intends to vigourously defend the lawsuit," it said. "Neither the science nor the facts support the allegations that have been made. Monster reiterates that its products are and have always been safe."
FDA spokesperson Shelly Burgess urged consumers who have experienced an adverse reaction to an energy drink to notify the manufacturers, which are required to report them to the administration within 15 days.
A report in November 2011 by the US Department of Health and Human Services found a tenfold spike in emergency room visits for issues linked to energy drinks between 2004 and 2009, totalling more than 16,000 visits in 2008, with sales of the beverages skyrocketing during that same period.
Aggressive marketing campaigns by such companies targeting susceptible youngsters have led to growing concern among authorities.
In August this year, federal prosecutors in New York summoned officials from Monster, PepsiCo and Living Essentials as part of a probe into the industry's advertising and marketing practices.
Energy drinks contain stimulants like caffeine, guarana and ginseng as well as the relaxant taurine and other vitamins.
