The Chicago-based manufacturers of Four Loko, a popular caffeinated alcoholic energy drink, were among the four recipients of a warning letter issued by the Food and Drug Administration, who claimed the caffeine used in their products was unsafe, according to the Associated Press.

The “FDA does not find support for the claim that the addition of caffeine to these alcoholic beverages is ‘generally recognized as safe,’ which is the legal standard,” Dr. Joshua M. Sharfstein, Principal Deputy Commissioner of the FDA said in a statement.

The Nov. 17 letter, sent to Four Loko, Charge Beverages, New Century Brewing and the United Brands Company said the use of caffeine in the companies’ alcoholic energy products could impair its consumers’ perception of intoxication. The FDA also stated that the government can seize the products, often called a “blackout in a can,” if no changes are made.

“Let these rulings serve as a warning to anyone who tried to peddle dangerous and toxic brews to our children. Do it and we will shut you down,” U.S. Sen. Charles Schumer (D-N.Y.) said in a statement. “This ruling should be the nail in the coffin of these dangerous and toxic drinks. Parents should be able to rest a little easier knowing that soon their children won’t have access to this deadly brew.”

Developers of the drinks came under scrutiny in recent months after several college students were hospitalized after consuming the drink. As a result, six states including New York, Michigan, Utah, Washington and Oklahoma have banned the beverages and other states are considering similar measures.

Maryland became the most recent state to ban Four Loko when state Comptroller Peter Franchot on Nov. 17 convinced two of the state’s beverage associations to stop distributing the drink to local stores, according to The Baltimore Sun. The state moved to ban the drink after the Nov. 7 death of 21-year-old Courtney Perry of Easton, Md. According to CBS affiliate WJZ-TV, Perry’s friends and relatives said she was drinking the beverage the night she crashed her pickup truck into two utility poles.

In response to the FDA’s letter, developers of Four Loko announced that it will remove caffeine and other ingredients from their product nationwide.

“We have repeatedly contended–and still believe, as do many people throughout the country– that the combination of alcohol and caffeine is safe,” the company’s founders said in a statement. “If it were unsafe, popular drinks like rum and colas or Irish coffees that have been consumed safely and responsibly for years would face the same scrutiny that our products have recently faced. By taking this action today, we are again demonstrating leadership, cooperation and responsible corporate citizenship.”

The beverages, which are sold in various flavors, contain as much alcohol as three beers and as much caffeine as three cups of coffee. Experts say teens have flocked to the drink because of its sweet taste and cheap costs.

But some speculate that the ban of the beverages will just lead to their illegal sale.

“They’ll start selling it out on the street,” Larissa Castro, 21, told the New York Daily News.

The FDA singled out these manufacturers and their products: Charge Beverages Corp. (Core High Gravity HG, Core High Gravity HG Orange, and Lemon Lime Core Spiked), New Century Brewing Co., LLC (Moonshot), Phusion Projects, LLC (Four Loko) and United Brands Company Inc.(Joose and Max).