One-fourth of high school students and 10% of middle school students say they use e-cigarettes, according to a new study by Food and Drug Administration researchers.

The findings suggest an estimated 4.1 million high school students and 1.2 million middle school students are using e-cigarettes, the researchers said. About one-third of teens who vape say they do so almost every day, HealthDay reports.

Among teens who used e-cigarettes, Juul use was reported by 59% of high school students and 54% of middle school students as their usual brand of e-cigarettes in the past month.

Among teens who used e-cigarettes but who didn’t use other tobacco products, an estimated 72% of high school students and 59% of middle school students used flavored e-cigarettes. The most commonly reported flavors were fruit, menthol or mint, and candy, desserts, or other sweets.