A new study finds that consuming a caffeine-infused energy drink combined with alcohol is more dangerous than drinking alcohol alone. The researchers say the findings suggest it may be appropriate to put warning labels on energy drinks saying they should not be mixed with alcohol, HealthDay reports.

The researchers studied 56 college students, splitting them into four groups. They drank either an alcoholic beverage, an energy drink, a drink that combined both alcohol and an energy drink, or a drink that did not include either one. According to a press release from the journal Alcoholism: Clinical & Experimental Research, they report that all the students who drank alcohol showed impaired impulse control. Those who drank the alcoholic energy drink, however, thought of themselves as less impaired than those who drank the same amount of alcohol alone. The researchers say this could make people who drink alcohol and energy drinks together more likely to do something risky like driving while drunk.

According to HealthDay, study co-author Cecile Marczinksi, Ph.D., of Northern Kentucky University, said what makes the combination of energy drinks and alcohol especially dangerous is that energy drinks have about three times as much caffeine as cola, making them extremely stimulating. She noted that the danger in combining caffeine and alcohol is that caffeine may make a person less aware of alcohol’s effect. The energy drinks do not change the level of a person’s impairment from alcohol, just their perception of it, the article notes.

In November, the U.S. Food and Drug Administration warned four companies that the caffeine added to their malt alcoholic beverages is an “unsafe food additive” and said that further action, including seizure of their products, is possible under federal law.