Teens who use e-cigarettes may be more likely to try marijuana in the future, especially if they start vaping at a younger age, a new study shows.
More than 1 in 4 teenagers who reported e-cigarette use eventually progressed to smoking pot, according to the survey of more than 10,000 teens.
That compared with just 8 percent of non-vapers, said lead researcher Hongying Dai, senior biostatistician with Children's Mercy Hospital in Kansas City, Mo.
Further, teens who started vaping early had a greater risk of subsequent marijuana use.
Kids aged 12 to 14 who used e-cigarettes were 2.7 times more likely to try marijuana than their peers, compared with a 1.6 times greater risk for teens who tried vaping between 15 and 17.
"Our findings suggest that the widespread use of e-cigarettes among youth may have implications for uptake of other drugs of abuse beyond nicotine and tobacco products," Dai said.
For the study, Dai and her colleagues twice surveyed 10,364 kids aged 12 to 17 -- once in 2013-2014, and again a year later.
The researchers found that teens who'd reported using e-cigarettes in the first wave were more likely to have tried marijuana for the first time during the subsequent year.
Results also showed that 12- to 14-year-olds who had tried e-cigs were 2.5 times more likely to become heavy marijuana users, smoking pot at least once a week.
Worse still, the researchers found that the more often young teens used e-cigarettes, the more likely they were to either try marijuana or become a heavy pot smoker.
Dai said the nicotine contained in e-cigarette vapor could be altering the brain chemistry of young teens.
"The brain is still developing during the teen years; nicotine exposure might lead to changes in the central nervous system that predisposes teens to dependence on other drugs of abuse," Dai said.
It's also possible that experimenting with e-cigarettes might increase a teen's curiosity about marijuana, and reduce any worries about marijuana use, Dai added.
Additionally, kids who use e-cigarettes could be more likely to run with a crowd that tries other substances, said Dai and Dr. Scott Krakower, assistant unit chief of psychiatry at Zucker Hillside Hospital in Glen Oaks, N.Y.
"E-cigarettes are going to be in the same drug culture as other things," Krakower said.
These findings should be concerning to parents because kids might not stop at trying marijuana, he said.
"If you go to marijuana, is that going to lead to pills? Is that going to lead to something else?" Krakower said. "When we see progression to another substance, it's like the 'and then what' cascade -- they went to marijuana, and then what?"
Since this is a survey, it can't prove a cause-and-effect relationship. And it's possible that wild, risk-taking teens who try e-cigarettes are predisposed to be adventurous with other drugs, Dai and Krakower said.
"It could be that they have more of that sensation-seeking personality, and if they pick up one they're going to pick up the other," Krakower said.
But Dai said her team took that into account, and even after adjusting for sensation seeking, "ever e-cigarette use was still significantly associated with subsequent marijuana use."
Krakower recommends that parents look for warning signs of e-cigarette use -- marked irritability, hiding things, skirting the truth -- and put their foot down hard.
"There should be zero tolerance for this kind of behavior," Krakower said.
Gregory Conley, president of the American Vaping Association, agreed.
"E-cigarettes are adult products and are not intended for youth of any age," Conley said. "We agree with the authors' conclusion that more education is needed to help young people understand the consequences of using age-restricted products and illicit drugs."
The new study was published online April 23 in the journal Pediatrics.
The U.S. National Institute on Drug Abuse has more about teens and e-cigarettes.
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