Luka Kinard knew his vaping habit was out of control when it started costing him $150 a week.

“I was selling my clothes,” Kinard, a 15-year-old high school sophomore, said. “I would get shoes, sell them, go out get cheap shoes, sell them. I was doing anything and everything to get money.”

His parents noticed when his grades started plummeting.

“He went from being a straight-A student to an F student,” Luka’s mother, Kelly Kinard, said. “(It was) a very rapid decline in grades. His behavior became explosive. He was very angry and it just wasn’t him.” Luka stopped his boy scouting activities, stopped fishing and spent all his time locked away in his room. He was vaping.

Luka is part of what the Food and Drug Administration and the Surgeon General call an epidemic of e-cigarette use. And, as with most teens who are taking up the habit, it was the slender, easy-to-conceal Juul device that really got him hooked.

Luka was hooked in a way that doctors never noticed before with regular cigarettes. “The flavor was better than the taste of a cigarette. Also the buzz was a lot better,” he said. But it was a pricey habit.

“When I started spending $17 every four days or every day it was getting to a problem,” he said. “I realized (I was spending) $150 on pods in a week, and I noticed like this was getting out of control.”

What brought matters to a head was when he had a seizure. “He was at his girlfriend's house and an ambulance was called and he ended up in at the emergency room,” Kelly Kinard said. She knew it was the Juuling that had done it.

“We followed up with the pediatrician, cardiologist and neurologist, and we couldn't get anyone to listen to us when we told them the seizure was preceded by Juuling,” she said. “I found on the internet that it should be treated like a substance abuse issue. That helped when I called the insurance company and told them we need a referral for a substance abuse treatment.”

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The High Point, N.C. teen ended up spending 40 days in an addiction rehabilitation program before he was able to kick his habit.

Luka Kinard, 15, of High Point NC, went through 40 days of rehabilitation therapy to help him kick a nicotine addiction fueled by e-cigarette use. Courtesy Kinard family

This makes sense to Dr. Sharon Levy, director of the Adolescent Substance Use and Addiction Program at Harvard Medical School.

“We've seen a real influx in the number of phone calls that we're getting for kids who need substance use evaluations and, remarkably, we're seeing a big increase in the number of kids who are coming in specifically to be evaluated for nicotine and Juuling problems,” Levy told NBC News.

“We're seeing kids that seem to be getting a much higher nicotine level in their blood and that’s causing a completely different picture when they come in.”

Other teams have found this, also, and the FDA is trying to crack down on sales of e-cigarettes to teens and young adults because they do deliver a much higher dose of nicotine than traditional burned cigarettes, Juul products, in particular, don’t offer a way to dial down the dose of nicotine-bearing vape fluid n the same way that other devices do.

The extra hit of nicotine can have especially strong effects on young bodies, Levy said.

“Kids are coming in with problems like difficulty in focusing, common symptoms of withdrawal, things like headaches, sometimes fatigue, stomach aches — which might be a symptom of nicotine toxicity or poisoning in some of them,” she said.

“We've had kids who come in and say that they can’t concentrate in school, that they need to leave the classroom, they need to sneak out to the bathroom so that they can hit their Juul, or that they need to go to the nurse's office because they just need to lie down,” Levy added.

“That's something we didn't see in use of cigarettes. This is very concerning. This is really uncharted territory and we don't know what use of nicotine in this way is doing to the developing adolescent brain.”

The FDA is holding a hearing Jan. 18 to start looking into what can be done to help teenagers who need to kick the vape habit. One question that will be asked: Could nicotine replacement therapy help?

“We have treated kids with things like nicotine replacement,” Levy said. “In some ways, it's a little ironic … but we're doing that and it seems to be helping for some of the kids.”

Too much nicotine is just like too much of any addictive substance, Levy said. “All substances of abuse, whether it's heroin or alcohol or marijuana, they are all causing firing in the same part of the brain that’s called the pleasure and reward center,” she said. “That’s what makes those substances feel good to people who use them.”

Rehab worked for Luka, who is back to normal, his mother said.

“We first noticed a change after three weeks when we could finally have a conversation,” she said. “We were allowed to talk to him every day, and we had our first conversation in 15 months.”

Luka is relieved, also. “I'm going back to scout meetings every Monday,” he said. “I'm going on a scout trip soon, so I'm taking it as a learning experience.”

Looking back, he can see what happened. At first, he just wanted to fit in. “Especially when you're in high school, you're a freshman, and you see a junior or a senior using it and you want to do what the older people are doing,” he said.

Juuling looked especially attractive. “It was better than smoking cigarettes for me because you know, the smell, when you walk into a room the odor isn't as potent and not everybody is looking at you,” Luka said.

And when his behavior started to change, he blamed his family and teachers instead of his nicotine habit. “I thought that everybody else was making me change. I didn't think it was smoking or anything like that — I thought it was just the fact that the world is against me, so I should be against the world.”

Kelly Kinard’s advice to other parents: Pay attention. “They need to react quickly. And they need to get treatment for their kids as soon as possible,” she advised.