Brazilian researchers report that “although drinkers said they felt less tired and had a heightened sensation of pleasure after quaffing a Red Bull, in actual fact, their abilities were still significantly impaired.”

“This is just the combination that might lead to very bad judgments," said Dr.

David L. Katz, an associate professor of public health and director of the Prevention Research Center at the Yale University School of Medicine. "Feeling less intoxicated and more alert, one might get behind the wheel of a car, but with impaired coordination and reaction time, that decision might spell disaster."

Results of the study by researchers at the Federal University of Sao Paulo, appear in the April issue of Alcoholism: Clinical & Experimental Research.  The study team assigned 26 healthy, young volunteers to two groups that received 0.6 or 1.0 g/kg of alcohol (vodka) respectively. All the volunteers completed three experimental sessions. These included alcohol alone, Red Bull energy drink alone, or alcohol plus the energy drink.

While the consumption of alcohol produced the expected effects, the combination of the two caused headaches often associated with over-consumption of alcohol as well as fatigue, dizziness, and weakness, and also altered sight, walk, hearing, and speech.

"The ingestion of one dose of energy drink was not enough to significantly reduce most of the objectively measured effects of alcohol in tests of motor coordination and reaction time, nor to reduce the breath-alcohol concentration," head researcher Maria Lucia Souza-Formigoni said.

She did add, however, that participants noted they experienced "a reduction in the subjective sensation of intoxication."  This is where the danger occurs, as those who’ve mixed the drinks think they have reduced the effects of the alcohol when, in reality, they have not.