The U.S. Food and Drug Administration (FDA) told beveragemakers in 2010 that their caffeinated, alcoholic drinks weren’t safe. Now, a new study bolsters that FDA claim, reports Ars Technica. Researchers found in a survey of 1000 college students that the more nonalcoholic energy drinks someone consumes, regardless of brand, the more likely they are to drive drunk. It’s unclear exactly why this is, they write in their study, published in Alcoholism: Clinical and Experimental Research, but they speculate that it’s because drinkers become less aware of their intoxication when they mix caffeine and alcohol. They also concede that the type of people who drink energy drinks might also matter, as they may have personalities that make them prone to driving drunk.