Monster Drink's Shares Slide After Calls for Regulation

What is this mysterious "caffeine" substance and how does it work?

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.