Just a week after issuing warning letters to four manufacturers of alcoholic energy drinks, the U.S. Food and Drug Administration announced the drink makers have made "significant progress" in complying with the agency's regulations.
Phusion Projects, the Chicago-based manufacturer of Four Loko, announced before receiving the FDA warning letter that it would remove caffeine-containing ingredients from their beverages. The company also said it will no longer ship its alcoholic energy drinks and would remove them from store shelves by December 13.
United Brands said it has stopped shipping its drink, Joose, and will also have products off store shelves by December 13. In addition, the company will no longer market Max, another beverage mentioned in the FDA's letter.
Charge Beverages and New Century Brewing told the FDA it will no longer manufacture any caffeinated alcoholic beverages, and Charge Beverages said it hasn't shipped any since early November.
The FDA issued warning letters to the companies after determining that caffeine is an "unsafe food additive." The letters also threatened further action if the companies did not comply.
While not an outright ban, the FDA said it's the first step in that direction.
"[It's] part of the process that FDA uses that leads to these products being removed from the market," said Dr. Joshua Sharfstein, the agency's principal deputy commissioner.
The Federal Trade Commission said in a statement that it also sent letters to the same four companies warning that marketing of the beverages may constitute an "unfair or deceptive practice that violates the FTC Act."
U.S. Senator Charles E. Schumer (D-N.Y.) issued a press statement before the letters were formally issued praising the FDA's action.
"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," said Schumer (D-NY).
The FDA warning letters come about a year after the FDA first decided to review the safety of caffeinated alcoholic beverages last November. The agency sent letters to about 30 manufacturers of these drinks alerting them of the review.
At the time the letters were sent, one of the issues the FDA said it planned to look into was whether it's legal to add caffeine to alcoholic beverages. Current regulations place significant restrictions on the addition of caffeine to beverages.
"The only way that caffeine is permitted to be added to beverages is to cola-type beverages in amounts not to exceed 200 parts per million, which is about twice the amount actually present in a can of Coca-Cola," said Dr. Mary Claire O'Brien, associate professor of emergency medicine at Wake Forest University Medical Center in Winston-Salem, NC.
"Though a lot of people are familiar with drinking a caffeinated beverage or an alcoholic beverage, few of them are familiar with drinking the combination," said Dr. Matthew Davis, associate professor of pediatrics and communicable diseases and an associate professor of public policy at the Ford School of Public Policy at the University of Michigan in Ann Arbor. "That combination is up to five beers at once in a single serving of a caffeinated alcoholic beverage and about the equivalent of one cup of coffee in terms of caffeine."
Many young adults drink caffeinated alcoholic beverages because they create a desirable feeling.
"They experience a high degree of intoxication due to alcohol and the caffeine has an effect that seems to override the intoxicating effects of alcohol. It's called 'wide awake drunk,'" said Bruce Goldberger, professor and director of toxicology at the University of Florida College of Medicine in Gainesville.
According to Goldberger, studies have shown that drinking caffeinated alcoholic beverages raises a person's blood alcohol concentration and also makes someone more likely to engage in risky behavior, such as driving while impaired.
"The amount of alcohol in a 23-ounce can is sufficient to produce a blood alcohol concentration above the statutory limit in all 50 states," Goldberger said.
A new study also highlights the dangers of mixing alcohol and caffeine. Researchers led by Amelia Arria, director of the Center for Young Adult Health and Development at the University of Maryland School of Public Health found that fourth-year college students who consumed energy drinks on a daily or weekly basis were at higher risk for alcohol dependence compared to their peers who drank them less frequently. The researchers kept other risk factors for alcohol dependence -- such as family history, age and behavior problems in childhood -- constant throughout the study.
"The association between energy drinks and alcohol dependence persisted even after we controlled for other risk factors," said Arria.
Arria also said the study did not look into why this association existed, and she said more research needs to be done to examine the relationship further. She added that this research drives home an important point.
"It underscores the potential public health risk of combining alcohol and energy drinks. It supports the fact that people who drink energy drinks are likely to mix them with alcohol, and that's likely to increase the risk for alcohol dependence," she said.
People need to know that there is a difference between drinks such as Kahlua and Coke, and pre-mixed alcohol and caffeine-containing drinks such as Four Loko and Joose.
"We haven't seen the level of problems associated with these other drinks as we have with the pre-mixed ones," said Arria.
"Those people who don't get it, and who don't understand the connection, may be more inclined to try these things for the first time because they're already combined," said Jeffrey Parsons, professor of psychology at Hunter College in New York.
Those problems have been well-publicized, such as the incident involving nine Central Washington University students who drank Four Loko and had to be rushed to the hospital.
As a result of this and other incidents, four states and a number of college campuses have banned the sale of alcoholic energy drinks. In New York, the State Liquor Authority and some of the largest beer distributors agreed to stop selling these drinks throughout the state.
Other experts think a ban could be counterproductive.
"I'm concerned that we're about to do for young people exactly what we've learned not to do," said Parsons. "The more we stigmatize something and make an issue out of it, the more attractive it's going to be."
He thinks there needs to be a much greater emphasis on how to prevent young people from picking up one of these drinks.
"I think we need, rather than just focusing on 'let's ban these products,' we need more research and prevention-based efforts to deal with the public health needs."
ABC News' Brian Hartman contributed to this report.