The science about long-term effects of the other chemicals and small metals in the vaporized liquids is unsettled, not only because formulations vary widely and are often undisclosed, but because e-cigarettes have not been around long enough to study thoroughly.

Some research suggests disturbing risks. A joint project between Duke and Yale’s Tobacco Center of Regulatory Science, published this fall in the journal Nicotine and Tobacco Research, found that when certain popular flavors are added to a common solvent in the vaping liquids, they produce chemicals that irritate airways and lungs. A 2016 study in the journal Chest said that smoking e-cigarettes had an effect on the heart and arteries which, while was not as pronounced as that of combustible cigarettes, was still distinctive.

Image The e-cigarettes are extremely discreet, making them particularly popular among high school and even middle school students. Credit... Joshua Bright for The New York Times

Perhaps what alarms public health experts most about e-cigarettes generally and Juul in particular is nicotine which, when vaporized, is absorbed by the body within seconds, much faster than when delivered by chewing gum or patches. Its potent addictive properties, doctors say, can be most pronounced in teenagers.

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After a few weeks of bumming daily hits from friends (called “fiending”), Matt went on a family vacation out West. On his second day without a Juul, he found he wanted one desperately. On the third, he couldn’t take it anymore.

He searched Juul’s website to find a local store that sold it, and ordered an Uber to get there, mumbling a nonchalant excuse to relatives. Between the cost of the ride service plus the Juul “starter” kit, he spent $100 to sate his need.

Soon, he escalated to a daily pod, sometimes more. He was spending $40 a week, draining his Christmas and birthday money, and his paycheck from his part-time job at Chili’s.