Party beverages that go by "blackout in a can" and other monikers may soon be banned from store shelves in some U.S. states, thanks to a number of incidents that have left drinkers unconscious and with dangerously high blood alcohol levels.

The Michigan Liquor Control Commission (MLCC) last week effectively prohibited the sale of all alcoholic energy drinks after considering several studies regarding such beverages as well as concerns voiced by substance abuse prevention and parental groups, the general public, and an ongoing U.S. Food and Drug Administration (FDA) investigation. The Commission called the packaging of these products "misleading," and an attempt to appeal to younger customers "encouraging excessive consumption while mixing alcohol with various other chemical and herbal stimulants." The ban takes effect in early December.

The MLCC pointed out that a typical alcoholic energy drink is 24 ounces (0.7 liters) and has a 12 percent alcohol content—compared with a 12-ounce (0.35-liter) can of beer, which normally has 4 to 5 percent—plus the caffeine equivalent of five cups of coffee. Some of the beverage lines singled out for their 12 percent alcohol content were Associated Brewing's Axis, United Brands's Max and Phusion Projects's Four Loko offerings. The commission concluded that a person need only consume one can of such a beverage to become intoxicated—and that because these drinks typically cost $2 to $5 per can they are "easily accessible and affordable."

Such beverages were in the news last month when nine Central Washington University students were hospitalized following a party. The blood alcohol levels of the students—who were all under the age of 21 at the time of the incident—ranged from 0.123 to 0.35. (A blood alcohol concentration of 0.3 can be lethal.) That school and others have since banned such drinks from campus pending further investigation.

Not far from Michigan, Chicago's City Council proposed its own ban on energy drinks that contain alcohol. Michigan and Oklahoma are the only states so far to ban such beverages, but New York is considering the same, and the Pennsylvania Liquor Control Board last week asked its licensed sellers to voluntarily stop selling and promoting alcoholic energy drinks such as Four Loko.

Whereas the combination of alcohol and caffeine is nothing new—rum and Coke, anyone?—this new breed of beverage is not meant to be sipped or served on the rocks. Scientific American asked Thomas Gould, an associate professor of psychology at Temple University in Philadelphia, to explain what happens to the body when large amounts of alcohol and caffeine are consumed simultaneously, why such drinks appeal to some drinkers, and the potential consequences of overindulgence.

[An edited transcript of the interview follows.]

What effect does the simultaneous consumption of alcohol and caffeine have on the body?
Alcohol is a sedative. It works in part by potentiating the GABAergic neurotransmitter system. GABA [gamma-aminobutyric acid] is an inhibitory neurotransmitter. When the neurons in the brain release GABA, it acts to slow down or inhibit other neural processes. This can reduce anxiety, increase relaxation while sedating a person. With higher levels of alcohol, problems can arise as important neural and other bodily systems become overinhibited and shut down.

Compared to alcohol, caffeine is on the other end of the spectrum of psychoactive drugs in that it is a stimulant. Caffeine is an antagonist for the neurotransmitter adenosine. Adenosine is an inhibitory neurotransmitter; so similar to GABA, adenosine can dampen or inhibit other neural processors. With caffeine, we have a double negative in that it inhibits an inhibitory neurotransmitter and thus increase levels of arousal and alertness—but higher doses can produce nervousness, anxiety and tachycardia.

One thing both drugs do is increase dopamine levels. Dopamine is a neurotransmitter associated with reward. One thing all drugs of abuse have in common is the ability to activate the dopamine system. The ability of alcohol and caffeine to stimulate the dopamine system may be one factor contributing to their use.

Because the drugs in a sense have opposite effects, one might expect that simultaneous consumption may reduce the effects that are seen when each drug is administered alone, but it really is not as simple as that. Some effects may be reduced while others are increased, and this may vary as the doses of the drugs vary.

Why might someone—an underage drinker in particular—want to drink a beverage that combines alcohol and caffeine?
Caffeine can reduce the sedative effects of alcohol; this may allow someone to drink for longer periods of time. In addition, evidence suggests that caffeine and alcohol together may be more rewarding than alone. This could be due to both drugs producing increases in dopamine levels, which as discussed is involved in reward.

However, caffeine does not decrease intoxication or reduce cognitive impairments associated with alcohol. Thus, the co-administration of caffeine and alcohol may facilitate the false perception that one is less intoxicated then they actually are. This could have detrimental effects.

Does this stem from the misconception some people have that coffee will sober them up after drinking? Why might someone believe this?
Yes, I believe this misconception may contribute to the co-use and abuse of these drugs. As mentioned, the ability of caffeine to increase arousal even in a drunk person may contribute to the false impression that an individual is either not impaired or intoxicated, when in reality the result is an alert drunk. A simulated drinking study conducted by Liguori and Robinson in 2001 illustrates this point. They found that alcohol impaired braking time and choice reaction time while caffeine partially ameliorated the effects of alcohol on braking but did not alter the deficit in choice reaction time. In fact, while caffeine did reduce the alcohol-induced braking deficit, braking time was still 9 percent slower than controls. The deficit in choice reaction time and impairment in breaking time could lead to accidents.

Is the consumption of these drinks a major problem, or is it a fad that will taper off the way wine coolers and Zima did?
The consumption of these drinks may lead to serious problems. If co-administration of alcohol and caffeine allow people to drink for longer periods of time because of reduced sedation, they may consume more alcohol; this could lead to serious health risks, such as near-lethal blood alcohol levels as seen in the Central [Washington] University case.

In addition, if the co-use of these give a false sense of security that leads an individual to believe they are less impaired then they are, they may be more likely to make poor decisions or put themselves in harm's way. In support, in 2008 Mary O'Brien et al. published the results of a study that examined college students who consumed either alcohol or alcohol–caffeine beverages and found that about twice many of those who consumed alcohol–caffeine beverages reported being taken advantage of sexually or being injured compared to those consuming only alcohol.

Another concern is that the adolescent brain is still developing; especially the prefrontal cortex, which is the part of the brain involved in decision-making and impulse control. The long-term effects of these drinks with combined high alcohol and caffeine content on the developing brain are not known, though problem alcohol use was associated with later depression [Mason, Kosterman, Haggerty, Hawkins, Redmond, Spoth and Shin, 2008].

Is there a concern that such drinks might be addictive?
Alcohol is addictive and people can become dependent on caffeine. The question is whether such drinks are more addictive. If the combined consumption of alcohol and caffeine leads to higher levels of alcohol consumption, then the risk for developing alcoholism is likely to increase.