E-cigs and weed – gateway to confusion between correlation and causation

Another study has confused correlation and causation when it comes to youth vaping and the supposed gateway effect – this time linking vaping and later cannabis use.

The study, “Use of electronic cigarettes among cannabis-naive adolescents and its association with future cannabis use”, published by the JAMA Network, found that young people who used e-cigarettes were up to 3.2 times more likely than their non-vaping peers to report future cannabis use.

While it may be tempting to interpret this as a “gateway effect” as it has been reported elsewhere what it demonstrates is correlation rather than causation: individuals who use e-cigarettes often also use cannabis, often at a later time. This, however, is no evidence that e-cigarette use leads to cannabis use. Ultimately, when viewed alongside the paper’s other findings as well as other research, this gateway theory falls apart.

The study found that while e-cigarettes did appear to increase the odds of later cannabis use at the individual level, when scaled up, “e-cigarette use seems to have had a minimal association with the overall prevalence of youth cannabis use. At the population level, adolescent use of cannabis has remained relatively stable for the past quarter century.”

The data was taken from surveys collected during the rapid uptick of vaping among adolescents seen in 2017. However, if the products functioned as a gateway to cannabis, a similar population level rise in cannabis would be expected to follow, which did not happen.


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    Most likely the findings can be explained by adolescents who are willing to engage in the risky behaviour of e-cigarette use being willing also to engage in the risky behaviour of cannabis use.

    While the researchers did control for some risky behaviours, it is difficult to capture and adjust for risk propensity entirely. Specifically, the authors evaluated the desire for “sensation seeking” by asking young people about their affinity for frightening things. However, while this might help control for some thrill-seekers, it does not necessarily capture the spirit of rebelliousness that often serves as the foundation for substance-related risk-taking in adolescence or for those who see nothing frightening in either e-cigarettes, cannabis, or both. 

    Additional research cited by the authors and using the same dataset (albeit at an earlier time) largely supports this idea. Here the authors find that the relationship between e-cigarettes and cannabis use is bidirectional: that is, while e-cigarette use may predict future cannabis use, cannabis use also predicts future e-cigarette use. Thus, rather than vaping somehow intrinsically causing future substance misuse, cannabis and e-cigarettes simply share common risk factors.

    It should also be noted that reported use of cannabis is always likely to be an underestimate due to the illicit nature of the substance and the continuing stigma attached to its use.

    Clayton Hale ECigIntelligence contributing writer

    Photo: Elsa Olofsson

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    This article was written by one of ECigIntelligence’s international correspondents. We currently employ more than 40 reporters around the world to cover individual vaping markets. For a full list, please see our Who We Are page.