The link between vaping and severe lung problems is getting a lot of attention.
But scientists say they're also worried about vaping's effect on teenage brains.
"Unfortunately, the brain problems and challenges may be things that we see later on down the road," says Nii Addy, associate professor of psychiatry and cellular and molecular physiology at Yale School of Medicine.
Potential problems include attention disorders like ADHD, impulse control issues and susceptibility to substance abuse.
There's no easy way to study precisely what nicotine is doing in a teenager's brain. But research on young animals shows that nicotine can interfere with processes that are critical to memory, learning, focus, impulse control and brain development.
"It's unfortunate that a whole generation of teenagers are basically guinea pigs for the effects of nicotine in the brain," says Frances Leslie, professor of pharmaceutical sciences at the University of California, Irvine.
Leslie says the problem is that nicotine mimics acetylcholine, an important chemical messenger in the brain. So nicotine is able to fool brain cells that have something called a nicotinic receptor.
Unfortunately, she says, "those parts of the brain that are actively maturing during adolescence are being actively controlled by nicotinic receptors."
Nicotine also acts on the brain's dopamine system, which plays a role in desire, pleasure, reward and impulse control.
It's still not clear what tweaking the dopamine system does to the brain of an adolescent human.
But in young mice, Leslie says, the result is alarming. "A very brief, low-dose exposure to nicotine in early adolescence increases the rewarding properties of other drugs, including alcohol, cocaine, methamphetamine — and these are long-term changes," she says.
Of course, nicotine-vaping products also contain lots of other substances, including flavors like bubblegum and pink lemonade. And Addy wonders whether these flavors might offer a dopamine kick of their own.
"If both nicotine and flavors are both acting on this same dopamine system in the brain," he says, "is that somehow facilitating and making it more likely that people will take products that have both flavors and nicotine?"
So Addy and a team of researchers studied rats that drank plain and flavored liquids containing nicotine.
"What we found is that the sweet flavors can make the nicotine more palatable in the oral cavity," he says, "but also act in the brain to increase nicotine taking."
This effect is especially troubling in a teenage brain, Addy says, which is more sensitive than an adult brain to rewards.
Animal research by another Yale University scientist suggests that vaping during adolescence can lead to long-term brain changes, like attention deficit hyperactivity disorder, Addy says.
"If there's exposure to nicotine early on, that can influence attentional processes later in life," he says.
So what might help reduce teen vaping?
One approach is to ban flavored products, something that was proposed by the Trump administration in September.
And if the ban happens, it could reduce the number of new vapers, says Janet Audrain-McGovern, a psychologist at the University of Pennsylvania.
Research shows that "if the first e-cigarette that you used was flavored, then you're more likely to go on and use an e-cigarette again," Audrain-McGovern says.
Another promising approach is to make nicotine-vaping products more expensive. When taxes forced up the price of tobacco products, Audrain-McGovern says, the number of young customers declined.
Finally, Audrain-McGovern thinks it should be harder for teenagers to buy vaping products online.
At the moment, many vaping websites simply ask visitors if they are underage before allowing a sale.
"I don't think it's that difficult to click the box that you're 18 or you're 21 and, if you have a credit card, to get those products," Audrain-McGovern says.
In August, Juul Labs launched a program that offers incentives to retailers that implement an age-verification system for customers.
But some measures that helped discourage smoking probably won't work as well against vaping, Audrain-McGovern says. For example, studies suggest that physically active teens are less likely than their peers to smoke but no less likely to vape.
Another challenge is that it's hard for scientists and regulators to keep up with the rapid pace of change in the vaping world.
"Teens who maybe four years ago were using predominately vape pens are now using Juul and some of the pod mods," Audrain-McGovern says.
And those newer products are designed to deliver higher levels of nicotine to the brain. More nicotine makes the products more addictive.
STEVE INSKEEP, HOST:
Across the United States yesterday, people held rallies aimed at encouraging teens and young adults who vape to quit. In Washington, D.C., activists demonstrated outside the offices of Juul, a company that's under the spotlight for its marketing practices. We have two stories this morning. NPR's Jon Hamilton explains what nicotine actually does to the teenage brain. And NPR's Allison Aubrey introduces us to a former vapor-turned-activist.
ALLISON AUBREY, BYLINE: On the very day that Piper Johnson's family was packing up the car to drive her to college, she started to feel sick, so she mentioned it to her mom.
PIPER JOHNSON: I went up to her, and I was like, my chest kind of hurts.
AUBREY: As they drove from the Chicago area to Colorado, Piper Johnson knew something was terribly wrong.
JOHNSON: I just kept feeling worse and worse.
AUBREY: Piper Johnson had been vaping since high school.
JOHNSON: I was vaping majority nicotine.
AUBREY: She also vaped some THC, but she didn't realize that vaping was making her so sick until she ended up in the ER.
JOHNSON: Oh, I was terrified. I had no idea what was happening to me.
AUBREY: As her oxygen levels plummeted, she was put in the ICU and remembers struggling to breathe.
JOHNSON: Honestly, it was the most painful experience of my entire life. Like, I was laying on my bed, like, sobbing because it hurt so bad to breathe.
AUBREY: She says she's feeling much better now. Not only has she stopped vaping, she can't believe she ever got hooked. And she wants to help other people quit, too. She says vaping is just so out of line with her generation's approach to good living.
JOHNSON: We're really, like, the generation of vegans, organic food - you know, mental health days and self-care days and stuff like that. But we're pumping our bodies full of chemicals without even knowing what it does to us.
AUBREY: And the outbreak of serious lung illnesses has helped to bring this into focus.
JOHNSON: People fail to realize that, like, you're deeply endangering yourself by doing this stuff.
JON HAMILTON, BYLINE: I'm Jon Hamilton. Vaping is dangerous - and not just for your lungs. Frances Leslie at the University of California, Irvine says the nicotine in vaping products can disrupt a developing brain.
FRANCES LESLIE: It's unfortunate that a whole generation of teenagers are basically guinea pigs for the effects of nicotine in the brain.
HAMILTON: Leslie says the problem with nicotine is that it mimics a substance we already have in our brains, so it can affect learning and memory and brain development. Leslie says nicotine's target is cells that have structures on their surface called nicotinic receptors.
LESLIE: Those parts of the brain that are actively maturing during adolescence are being controlled by nicotinic receptors.
HAMILTON: Nicotine also acts on brain areas involved in addiction. It's still not clear precisely how that affects an adolescent human. But Leslie says in adolescent mice, the result is alarming.
LESLIE: A very brief low-dose exposure to nicotine in early adolescence increases the rewarding properties of other drugs, including alcohol, cocaine, methamphetamine. And these are long-term changes.
HAMILTON: Nicotine itself is addictive because it activates the brain's dopamine system. But Dr. Nii Addy at the Yale School of Medicine wondered whether the flavors added to vaping products might also activate this system.
NII ADDY: If both nicotine and flavors are acting on this same dopamine system in the brain, is that somehow facilitating and making it more likely that people will take products that have both flavors and nicotine?
HAMILTON: To find out, Addy and a team of researchers studied rats.
ADDY: What we found is that the sweet flavors can make the nicotine more palatable in the oral cavity but also act in the brain to increase nicotine taking.
HAMILTON: Addy says this finding is especially troubling when it comes to teenagers, whose brains are extra sensitive to rewards. And he says animal research by another Yale scientist suggests that young people who vape may be more likely to develop brain disorders, like ADHD.
ADDY: If there is exposure to nicotine early on, that can influence attentional processes later in life.
HAMILTON: So what might help reduce teen vaping? Janet Audrain-McGovern, a psychologist at the University of Pennsylvania, says a ban on flavors like bubblegum and pink lemonade could make a difference.
JANET AUDRAIN-MCGOVERN: If the first e-cigarette that you use was flavored, then you're more likely to go on and use an e-cigarette again.
HAMILTON: Audrain-McGovern also thinks fewer teens might vape if nicotine products were more expensive and harder to buy online.
AUDRAIN-MCGOVERN: I don't think it's that difficult to click the box that you're 18 or you're 21 and, if you have a credit card, to get those products.
HAMILTON: But she says it's going to be hard for regulators and scientists to keep up with all the changes in the vaping world.
AUDRAIN-MCGOVERN: Teens who maybe four years ago were using predominantly vape pens are now using Juul and some of the pod mods.
HAMILTON: Products that can deliver much higher levels of nicotine to their brains.
AUBREY: Allison Aubrey, NPR News.
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