Preparing and serving mixed drinks that combine caffeine and alcohol in bars, parties or elsewhere is legal, however.
The stimulation from caffeinated alcoholic drinks counters the sedating effects of alcohol, making drinkers feel like they're not quite as affected by the liquor, Marczinski said. However, the energy drinks don't alter the level of behavioral impairment, just the perception of it.
"I'm most concerned about impaired driving," she said. "Typically, a lot of people's judgment is not good even at the best of times when they're drinking alcohol. It's really that sleepy feeling that cues people it's time to go home. This might extend the whole party experience longer than it should."
She and the other researchers noted that further studies are needed to determine whether the energy drink cocktails are escalating risky drinking practices among young people, who already demonstrate high levels of binge drinking.
The study is published online in advance of the July 2011 print issue of Alcoholism: Clinical & Experimental Research.
Bruce Goldberger, director of toxicology at the University of Florida College of Medicine, said his research in this area indicates that drinkers are more likely to drive if they mix alcohol with energy drinks. Other studies show increased risks of violence, unprotected sex and even sexual assault among those who consume this combination, he said.
"There's this perception that if you drink caffeine, it will sober you up, and it's just completely not true," Goldberger said. "Because the effects of the caffeine work in one region of the brain and the effects of the alcohol work in another, so they don't cancel each other out. Some people call it wide-awake drunk."
The U.S. National Institute on Alcohol
All rights reserved