Feb. 12, 2010 -- College-age drinkers who swill alcoholic energy-drink cocktails are three times more likely than alcohol-only drinkers to leave a bar drunk.
What's more, those imbibing energy cocktails are four times more likely to attempt drunken driving, find University of Florida researchers Dennis Thombs, PhD, and colleagues.
"Combining energy drinks and alcohol can trick the brain, making people think they're sober -- or sober enough -- when they're not," Thombs tells WebMD.
As many as 28% of college drinkers drink alcohol mixed with energy drinks in a typical month, Thombs and colleagues note.
Between 10 p.m. and 3 a.m., Thombs' team interviewed 800 patrons leaving bars in a college partying area. They asked about their drinking and about whether they intended to drive. Then they checked their breath alcohol concentration levels.
The results are sobering.
- 6.5% had drunk alcohol-energy drink combos.
- 6.6% had drunk energy drinks and alcohol, but not mixed together.
- 86% had drunk alcohol only.
- The average breath alcohol reading for those who drank energy cocktails was 0.109, higher than the legal driving limit of 0.08. The average breath alcohol concentration for those who had alcohol only was 0.081.
- Those who combined alcohol and energy drinks drank for longer periods of time.
- Patrons drinking energy cocktails left bars later than those who drank alcohol only.
"Often, students drink energy drinks because they are tired and don't start until late and want to have enough energy," Thombs tells WebMD. "They drink these before they go out. Then there's a group that combines alcohol and energy drinks; the most common is Red Bull and vodka."
The phenomenon is so common, he tells WebMD, that researchers have coined an acronym for it: AMED, for alcohol-mixed-with-energy-drinks.
Study researcher Bruce Goldberger, PhD, director of toxicology at the University of Florida, says consumers of energy drinks may drink more and misjudge their capabilities because caffeine reduces drowsiness felt by more intoxicated people.
This condition is often described as "wide awake and drunk," Goldberger says in a news release.
People often think the stimulant effect of caffeine counteracts the depressant effect of alcohol, but that's not true. Stimulants actually aggravate intoxication.
The study notes that the market for high-caffeine-content energy drinks has grown exponentially since the introduction of Red Bull in 1997. Many such energy drinks are now on the market.
The study appears in the April issue of the journal Addictive Behaviors.