MONDAY, March 16, 2020 (HealthDay News) -- Many U.S. teens and young adults have no idea much nicotine is in the vaping products they use, a new study says.

Researchers asked 445 17- to 24-year-olds in California about their tobacco and nicotine use, especially the use of pod-based e-cigarettes, such as Juul. The devices, which resemble computer thumb drives, consist of a plastic pod of nicotine-infused fluid that snaps into a vaporizer.

About 26 percent of participants had used Juul; 24% had smoked traditional cigarettes; 23% had used nonpod-based e-cigarettes; and smaller percentages had used other pod-based e-cigarettes.

They didn't know how much nicotine was in the products.

When the surveys were done, Juul's packaging just said "5%" on the label. That's since been changed to say "5% nicotine."

But participants couldn't calculate what this meant in terms of nicotine quantity, or compare it accurately with the amount of nicotine in combustible cigarettes, according to the study published online March 16 in the Journal of Adolescent Health.

"These young people had no idea how much nicotine they were consuming," said senior author Bonnie Halpern-Felsher, a professor of pediatrics at Stanford University.

"If we asked how many milligrams of nicotine are in a Juul pod, for example, we found the answers were all over the place," she said in a university news release. "The Juul and other pod-based e-cigarette packaging is so confusing and misleading. The packaging should be regulated."

Pod-based e-cigarette users said they chose those products mainly because they're easy to hide (58%) and the smell they emit is less noticeable than other types of e-cigarettes (55.6%).

"Teens are not using these pod-based products more than other e-cigarettes because of health or the flavors offered," Halpern-Felsher said. "They tell us, 'It's because we can hide these, and the smell produced is less obvious.' This ability to 'stealth use' is concerning."

More information

The U.S. National Institute on Drug Abuse has more about e-cigarettes.