An agency spokesperson acknowledged the reports Monday, but said they don't prove the drinks caused the deaths.
The investigation follows last week's filing in California of a wrongful death lawsuit filed by the parents of 14-year-old Anais Fournier, who according to the suit, died of heart problems after drinking two 24-ounce Monster drinks within 24 hours.
"I told them what had happened," said Fournier's mother, Wendy Crossland. "I told them that I found out she had drank the energy drink and they said that that was a very good possibility of what had caused it, and then I got the death certificate which stated cardiac arrhythmia due to caffeine toxicity."
Fournier died last December. An autopsy report shows the teen also had an inherited disorder which can weaken blood vessels. Her parents say Corona-based Monster Beverage Company needs a warning about the risks of drinking its products.
In a statement Tuesday, Monster said it is "saddened by the untimely passing of Anais Fournier, and its sympathies go out to her family. Monster does not believe that its products are in any way responsible for the death of Ms. Fournier and intends to vigorously defend the lawsuit."
The first scheduled hearing will take place in a Riverside County courthouse in April 2013.
Preventive health specialist Dr. Ken Stewart of the University of California at Riverside said children and teens should not consume caffeine in large amounts. He said too much can cause health problems, from rapid heartbeats to vomiting.
"I would advise parents don't give your kids caffeine," Stewart said. "Monitor what they are doing."
According to the Mayco Clinic, two 24-ounce Monster Energy drinks contain 480 milligrams of caffeine. That's the equivalent of about five eight-ounce cups of coffee, or about 14 cans of cola.
While the FDA regulates the amount of caffeine in soft drinks, it does not with energy drinks, which are sold as dietary supplements.