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‘Highly illogical, captain’

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.

Of course, while the e-cigarette world is painfully accustomed to this kind of fuzzy thinking, other novel nicotine products such as heated tobacco and pouches have so far been largely spared it – as they have generally been spared scare-driven media coverage and apparently headline-driven scientific research.

But as they grow in popularity, it is surely only a matter of time before dubious links are drawn between use of a safer nicotine product and use of some other substance, be that cannabis or combustible tobacco or saturated fats.

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.


‘Minimal association’


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.”

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    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. 

    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.


    Doesn’t wheat cause mice?


    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.

    So, when you first hear the suggestion that (say) nicotine pouches “lead to” drinking alcohol, apply the correlation/causation test. Two phenomena may well be frequently found together, but does that mean one causes the other?

    We might laugh at the 17th century speculation that wheat created mice (the two only correlate), but sometimes our 21st century thinking on controversial substances falls into the same error.

    Clayton Hale contributing writer and Barnaby Page TobaccoIntelligence staff

    Photo: Olga Nohra

    Barnaby Page

    Editorial director
    Before joining ECigIntelligence in early 2014 as one of its first employees, Barnaby had a 30-year career as a reporter and editor for newspapers, magazines and online services, working in Canada, the US and the Middle East as well as his current British location. He has edited publications covering fields including technology and the advertising industry, and was launch editor of the first large daily online news service in the British regional media. Barnaby also writes on classical music and film for a number of publications. Barnaby manages the editorial and reporting teams and works closely with the analyst teams, to ensure that all content meets high standards of quality and relevance. He also writes for the site occasionally, mostly on science-related issues, and is a member of the Association of British Science Writers.