Also, there have been several recent incidents where students were hospitalized after drinking Four Loko.
In response to such incidents, Washington, Michigan, Utah and Oklahoma have banned the beverages, and other states are considering the same.
The action essentially bans those drinks from store shelves.
One of those drinks is called Four Loko, which comes in several varieties, including fruit punch and blue raspberry. A single-serving 23.5-ounce can sells for about $2.50 and has an alcohol content of 12 percent, comparable to four beers, according to the company's website.
Late Tuesday, its maker announced it would reformulate its drink and remove caffeine. The FDA also issued warning letters to Charge Beverages Corp., New Century Brewing Co. and United Brands Company Inc.
The government could eventually seize the products if the companies continue to make and market them. The companies have 15 days to respond to the letters and either explain how they will take their products off the market or defend their drinks as safe.
The Associated Press contributed to this report.
