Adolescents who used e-cigarettes were significantly more likely to become new smokers of cannabis shortly thereafter, a cohort study found.

Cannabis-naive adolescents reporting ever vaping at baseline were more than twice as likely to report also using cannabis when surveyed a year later (adjusted RR 2.57 vs nonusers of e-cigarettes, 95% CI 2.04-3.09), reported Ruoyan Sun, PhD, a health behavior researcher at University of Alabama at Birmingham, and colleagues.

Marijuana use within a year was similarly likely to begin whether e-cigarette use started in the 12 months or 30 days preceding baseline, according to the study in JAMA Network Open.

“However, despite the strong association at the individual level, e-cigarette use seems to have had a minimal association with the prevalence of youth cannabis use at the population level,” Sun’s group cautioned, noting that “the prevalence of adolescent cannabis use at the population level has remained relatively stable from 1995 to 2020 among adolescents in 8th, 10th, and 12th grade.”

It may be that the population studied — cannabis-naive adolescents who have tried e-cigarette — is too small to make a dent at the population level. Another possibility is that many adolescent e-cigarette users simply experiment with marijuana without becoming established users, according to the investigators.

E-cigarettes were first introduced to the U.S in 2006 and have since attracted young users in part because of appealing flavors. The popularity of vaped marijuana among teenagers increased from 2017 to 2019, while cannabis use without vaping fell during this period, a recent study showed.

Last month, FDA ordered popular vape products from Juul off the market, citing public health concerns, though the decision remains under review. Research suggests that many adolescents and young adults have become new tobacco users recently because of Juul products.

“One reason that understanding the correlates and outcomes of e-cigarette use is important is because e-cigarettes have rapidly increased in popularity to become a predominant substance of misuse among U.S. youths,” commented Wilson Compton, MD, MPE, and Emily Einstein, PhD, both from the NIH’s National Institute on Drug Abuse in Bethesda, Maryland.

“[E]xposure of the adolescent brain to nicotine may affect brain development and may increase the risk of addiction,” they said in an editorial. “Nicotine has been shown to potentiate the rewarding properties of other substances, potentially including cannabis, which could be one mechanism by which e-cigarettes could increase subsequent cannabis use.”

“Regardless, even with the contribution of potential biological mechanisms, the ‘gateway’ properties of any drug are intensely driven by social and environmental factors that may lead to the initiation and progression to further drug use, which may be successfully targeted by existing evidence-based prevention interventions,” Compton and Einstein suggested.

The study was based on the PATH cohort, a representative cohort of survey participants 12-17 years of age from the U.S. civilian, noninstitutionalized population.

The present analysis included 9,828 participants (57.3% age 12-14, 50.7% boys, and 53.0% non-Hispanic white) who completed a baseline survey during wave 4.5 (2017-2018) and a follow-up survey in wave 5 a year later (2018-2019).

Surveys assessed their e-cigarette and cannabis use. Data were adjusted for sociodemographic information such as age, sex, ethnicity, parental education, household income, and school grades.

In the wave 5 survey, 10.7% of respondents reported cannabis use in the prior year and 4.7% in the past 30 days. For e-cigarette users at baseline, 38.8% reported cannabis use over the past year in the wave 5 survey versus 8.3% of those who never used e-cigarettes. Past 30-days cannabis use rates were 19.3% and 3.4%, respectively.

Legalization of cannabis in several states may have affected study results, Sun and colleagues acknowledged, noting that a lack of geographic information prevented them from controlling for state-level cannabis legalization.

Another limitation was the exclusion of participants due to missing data, which may affect generalizability.

Finally, PATH survey questions on past 30-day cannabis use did not specify cannabis use through hookah or electronic products, according to the authors.

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