The FDA is investigating reports of 13 deaths of people who took 5-Hour Energy beverage shots made by Living Essentials.
Agency officials say they will take action if they can link the deaths to the product's consumption.
Energy drink makers are facing more intense scrutiny following reports and lawsuits that allege the highly-caffeinated products are tied to deaths.
The FDA last month said it was investigating reports of five deaths in which the consumption of Monster drinks was cited.
Monster stock is volatile Thursday, dropping as much as 5 percent in early trading. At midday, the stock is off 1.5 percent at $44.07.
(Copyright 2012 by The Associated Press. All Rights Reserved.)