NEW YORK (AP) -- Shares of Monster Beverage Corp. slid again Friday after two U.S. senators asked federal regulators to fix what they say are loopholes that allow energy drink makers to sell products with additives and high levels of caffeine they say "have not been proven safe."
The letter to the Food and Drug Administration from Sens. Dick Durbin, D-Ill. and Richard Blumenthal, D-Conn., comes after the agency announced this week that it was investigating reports of five deaths in which the consumption of Monster drinks was cited.
Those claims say that people suffered adverse reactions after consuming Monster Energy Drink, which comes in 24-ounce cans and contains 240 milligrams of caffeine, or seven times the amount of the caffeine in a 12-ounce can of cola.
The FDA noted that the allegations, which date back to 2004, don't necessarily prove that the drinks caused the deaths.
In a letter Friday, Durbin and Blumenthal cited a recent study in Consumer Reports that found several popular energy drinks contained significantly more caffeine than the listed amount, while others didn't disclose the amount of caffeine they had.
The FDA caps the amount of caffeine in soda to 0.02 percent, but there is no such limit for energy drinks.
Durbin and Blumenthal also noted that this is the third time this year they asked the FDA to assess the safety of energy drinks.
A representative for Monster Beverage said the company was not commenting on the matter. A representative for the FDA did not immediately respond to request for comment.
This summer, New York state Attorney General Eric Schneiderman also issued subpoenas to energy drink makers as part of the state's investigation of the industry.
Shares of Monster Beverage, based in Corona, Calif., fell $1.24, or 2.6 percent, to $45.85 in afternoon trading. They fell to a 52-week low of $40.06 on Tuesday.