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In 2010, the Food and Drug Administration sent letters out to beverage makers warning that their caffeinated, alcoholic drinks were “unsafe.” The federal admonishment followed an exceptional string of reports that college kids were getting black-out drunk and severe alcohol poisoning after consuming them. Mixing alcohol and high levels of caffeine is a dangerous combination, the FDA and health experts cautioned; the drinks amp people up while dousing their ability to sense their own intoxication, leading to more drinking and riskier behavior.

But according to new research, highly caffeinated beverages can be linked to serious trouble.

In a six-year study following 1,000 college students, researchers found that the more non-alcoholic energy drinks a person reported throwing back, the more likely they were to drive drunk. The finding squares with past studies that have linked alcoholic energy drinks to such dangerous behaviors. However, the study, published Tuesday in Alcoholism: Clinical and Experimental Research, is the first to decouple the bad effects of alcohol from those of the energy drinks alone.