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3.1–7.9). Similarly, 18–21 were a little over two times more likely (OR: 2.08, 95% CI: 1.4–3.1) to be e-cigarette users as compared to those aged 22–24. Additionally, males were 2.28 times more likely to be e-cigarette users compared to females (OR: 2.19, 95% CI: 1.5–3.4).This study sheds light on the prevalence of and factors associated with e-cigarette use in youth and young adults in Canada. In 2017, the national prevalence rate for past 30-day e-cigarette use among this population was 6.2%. This finding is similar to reports from the 2015 CTADS survey (6%) [30], however greater than the 2013 results which suggested less than 4% past 30-day e-cigarette use in this demographic [29]. The prevalence of ever and past 30-day use of e-cigarette was highest in the province of Newfoundland and Labrador, with the lowest reported prevalence in Ontario. Among other factors, this study also shows that using marijuana and alcohol, being a current cigarette smoker, and being male are significantly associated with past 30-day e-cigarette use. Moreover, illicit drug use approached significance with past 30-day e-cigarette use. After adjusting for socio-demographic and health related factors, tobacco use variables, and substance use variables, the use of e-cigarette in illicit drug users was significantly higher than non-drug users. Due to the lack of studies on the dual use of illicit drugs and e-cigarettes in Canada, it is not possible to compare these results to previous Canadian data to assess trends. However, some international studies have shown findings similar to those in the present study [15–17, 34]. Additionally, even fewer studies have explored the potential use of e-cigarettes as illicit drug delivery systems. Blundell et al. (2018), using convenience samples, and Breitbarth et al. (2018), using illicit drug forums, found that drugs such as methamphetamine, ecstasy, cocaine, heroin and fentanyl have the potential to be smoked through e-cigarettes and come with the added advantage of losing their characteristics odours, making them easier to disguise in public settings and from police officials [5, 18]. Once explored further, these findings would warrant stricter rules around smoking e-cigarettes in public settings, as dual delivery has the potential of exposing the public to nicotine smoke as well as illicit drugs. Having said that, more research is needed in the area of substance use via alternative drug delivery systems, in order to clearly understand the mechanisms of their use as well as the risks posed by e-cigarettes. The present study also showed that marijuana users were significantly more likely to be past 30-day e-cigarette users, compared to non-users. Some studies suggest that vaping of cannabis extracts is becoming more common among marijuana users [19, 35, 36] due to its perception of being less harmful than the traditional burning to smoke methods [4], being easier to disguise due to reduced odours [35], and stimulating less throat irritation upon smoking [37]. Additionally, it is important to note that the current study utilizes results from a survey conducted in 2017, when cannabis was still considered an illegal substance in Canada. In October of 2018, the Cannabis Act legalized the possession and use of cannabis across the nation. This may have implications for the association between marijuana and e-cigarette use in the coming years, and the authors predict that this association will become exacerbated with time. Finally, the association between using alcohol and e-cigarettes has also been noted in other studies [20–22]. However, it is unclear what underlies this association. Hershberger et al. (2016) suggests that the combined use might exist to offset the sedating effects of alcohol via nicotine, while increasing the dopaminergic reward system stimulation through the combination of both substances [38]. While substance use and e-cigarette use were common in the current study, more studies are required to assess the temporal order of these two behaviors. Among the tobacco exposure and use variables, those who had one or more smokers in their household were significantly more likely to have used e-cigarette in the past 30-days, as compared to those belonging to non-smoking households. This is