Bar patrons who consumed energy drinks mixed with alcohol were three times more likely to leave drunk and four times more willing to drive drunk compared to patrons who drank alcohol alone, according to researchers who surveyed college-aged drinkers as they left bars.

The University of Florida researchers surveyed more than 800 bar patrons at random between the hours of 10 p.m. and 3 a.m., and also collected breath samples to test blood-alcohol content (BAC). The average BAC for alcoholic energy drink consumers was 0.109 percent, well above the legal standard for intoxication.

Patrons who consumed alcohol mixed with highly caffeinated energy drinks like Red Bull also were more likely to have consumed alcohol for longer periods of time, and left bars later than other drinkers.

The study was led by Dennis Thombs of the school's College of Public Health and Health Professions. "His approach is unique because it was conducted in a natural drinking environment -- college bars," said Wake University's Mary Claire O'Brien, author of previous research on alcoholic energy drinks. "His results clearly support the serious concern raised by previous research, that subjective drunkenness may be reduced by the concurrent ingestion of caffeinated energy drinks, increasing both the likelihood of further alcohol consumption, and of driving when intoxicated."

The study was published in the journal Addictive Behaviors.