“Adolescents have a brain that’s still changing and developing,” said Dr. Nicholas Chadi, the lead author on the study, who conducted the research as a fellow in pediatric addiction medicine at Boston Children’s Hospital and Harvard Medical School.
When a young brain is exposed to an addictive substance such as nicotine, it “tends to be sensitized to other substances; it tends to seek a thrilling, rewarding sensation,” said Chadi. “And so other substances like marijuana become more appealing.”
That link suggests that “e-cigarettes really need to be considered in the broad category of addictive and harmful substances,” said Chadi, who is now an assistant professor at the University of Montreal.
“We can’t think of e-cigarettes as a less-harmful alternative to cigarettes with adolescents,” he said, in part because “just like cigarettes, e-cigarettes increase your risk of using marijuana, and marijuana, we know, has several implications and negative health consequences in adolescents.”
Review looked at correlation, not causation
Studies included in the new review looked for correlation, not causation, meaning that researchers couldn’t prove that e-cigarettes directly caused increases in cannabis use. But when it comes to figuring out why marijuana use consistently increased in those who vaped, Chadi said “it’s hard for me to find a better explanation.”
“A reasonable hypothesis,” he said, “is that e-cigarette use might cause at least a part of that increased risk of using marijuana.”
Most of the 21 studies included in the review adjusted for gender, age, race and socioeconomic status, said Chadi. Research works best “by adjusting all of those factors, and repeating the same study in different parts of the world and using different designs,” he said.
“The more times you do that, the less chances you have of finding an association that’s not there, that’s not true,” he added.
Compared to young adults ages 18 to 24, teens younger than 17 were also more likely to use marijuana if they vaped, the review found. “The relationship seemed to be stronger in younger people versus older people,” said Chadi. That makes sense, he said, because “a younger brain is more vulnerable to the effects of substances in general.”
If a younger teen is exposed to e-cigarettes, “you would expect that there would be a higher risk of them using marijuana, versus an older adolescent or young adult who might have a more developed brain and might not be as sensitive to the negative effects of nicotine,” he added.
Developing brains are more vulnerable, experts say
He added that “the circuits underlying pleasure and the pursuit of novel, enjoyable experiences develop much faster than the circuits that promote decision making, impulse control and rational thinking.”