Teen users of popular “pod” vaping devices like JUUL brands are exposed to a higher amount of nicotine than with traditional cigarettes and older generations of e-cigarettes, according to a study published Friday in the journal Tobacco Control.

The Food and Drug Administration is investigating JUUL’s popularity among teens and adolescents as part of a larger crackdown on e-cigarette use among minors. A 2015 study from the Centers for Disease Control and Prevention found that e-cigarette use among middle and high school students tripled from 4.5 percent in 2013 to 13.4 percent in 2014.