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Some experts said the higher vapor could potentially make the pods even more addictive, increasing the risk particularly to young people, whose developing brains are more susceptible to the addictive qualities of nicotine.

Micah Berman, associate professor of public health and law at The Ohio State University, said the amount of nicotine in a pod can be deceptive — what really matters is how much the body actually absorbs.

“One of the things with cigarette design over the years is that they have figured out how to maximize the impact of nicotine in cigarettes,” Mr. Berman said.

Of Juul’s plans, he said: “If it’s a change that reduces test levels of nicotine — the amount you would identify as being in the pod itself — but doesn’t actually change the biological level, then that’s certainly problematic. It’s more like cheating the test.”

But Neal Benowitz, a professor of medicine at the University of California, San Francisco, said that increasing the vapor might indeed make Juul more useful to smokers who want to quit.

“For smoking cessation, you need to have a satisfying delivery system with a good amount of nicotine with a small amount of aerosol,” Dr. Benowitz said. “But if you are vaping because you like the sensory aspects of it, then you want more aerosol. Right now, Juul is a good nicotine delivery device but the quality is not the same as a cigarette. I could see why some people might like a product that generates more aerosol and is more cigarette-like.”

The new pods are expected to be slightly longer than the existing pods, but are designed to fit the current Juul device.