In most Western countries, cigarette smoking remains the dominant form of nicotine use [1]. However, in recent years, the use of other devices for nicotine consumption, in particular vapourizers, have become increasingly common. Commercial vapourizers emerged in the late 1990s as an alternative mode of cannabis use. These vapourizers were typically large devices that heated dried cannabis herb below the point of combustion to the point of vapourization [2]. Beginning in 2003, smaller, portable vapourizers emerged as ‘electronic cigarettes’ and heated nicotine in a solution rather than from dried leaf, as was the case for the early cannabis vapourizers. More recently, vapourizers in the cannabis market have followed a similar transition, with greater use of cannabis extracts in oil ‘pods’ or vape pens, alongside devices that use dried herb [3,4,5]. This is expected to further expand as cannabis companies partner with tobacco companies to benefit from vaping technology [6]. The current paper uses the term ‘e-cigarette’ or ‘vaping’ to refer to nicotine and other non-cannabis forms of vaping while ‘cannabis vaping’ is used to refer to the cannabis-specific mode of administration.

E-cigarette use is most prevalent among youth and young adults in countries such as Canada, England, and the United States (U.S.). While the sale of e-cigarettes and e-liquids is illegal for minors to purchase in these countries, they are still widely accessed by youth [7]. Recreational cannabis is currently legal in 11 U.S. states and in Canada, as of October 2018. Medical cannabis is legal in 33 U.S. states and has been legal in Canada since 2001. The minimum legal age for e-cigarettes and cannabis is 18 or 19 in Canada (depending upon province of residence); in the U.S., the minimum legal age for e-cigarettes ranges from 18 to 21, and is 21 for cannabis in all states in which it is legal. E-cigarette use has increased over the past decade in all three countries, although to different extents [8,9,10]. Substantial increases in youth vaping were observed between 2017 and 2018 in Canada and the U.S., consistent with increases in JUUL, the leading brand of nicotine vaping devices in North America, and other nicotine salt ‘pod’ devices [7,10,11]. Over the same period, smoking tobacco has declined, although smoking rates may have stabilized more recently [8,10,12]. E-cigarettes can be used with or without nicotine-containing liquid or ‘juice’ [13]. A review looking at published studies of e-cigarette prevalence among youth between 2014 and 2016 found that most studies did not report whether nicotine or non-nicotine products were being used [14]. In Canada, it was reported that about 4% of Ontario high school students reported using an e-cigarette with nicotine, while 10% used non-nicotine liquids [15]. Data from a nationally representative sample of U.S. students found that among e-cigarette users, about 20% of 10 and 12th graders, and 13% of 8th graders used nicotine, while about 65% across all grades reported using non-nicotine products [16].

There is less published evidence on cannabis vaping among youth. Despite varying legal availability of cannabis products for adults in Canada, England and the U.S., the sale of cannabis to minors remains illegal in all three countries. While smoking cannabis remains the most common method of use among adults and youth, alternate modes of delivery, such as edibles and the use of e-cigarettes to vape cannabis products, are becoming increasingly popular [5]. A recent survey of adolescent cannabis users in the U.S. found that smoking was the most common mode of intake; however, almost half reported lifetime cannabis vaping [17]. Studies with U.S. college students have reported lifetime cannabis vaping prevalence ranging from 9% to 29%, while prevalence among high school students has been reported between 5% and 9% [18,19,20,21]. There are less data available on modes of cannabis use among youth in Canada and England. A study of students in Canada’s largest province, Ontario, reported that 8% of high school students aged 15–18 vaped cannabis [22]. Studies have consistently found a positive association between e-cigarette use and cannabis vaping, including among youth [18,19,20,21,23]. More research is needed to better understand not only what nicotine and cannabis products young people are using, but how they are consuming them.

One important methodological question is the extent to which population-based surveys are able to distinguish between vaping nicotine and cannabis. The language used to refer to “e-cigarette use” has evolved over time: ‘vaping’ is now widely used to refer to both ‘e-cigarettes’ and using a vapourizer for cannabis, alongside the emergence of new terms, such as “JUULing”. The terminology used to determine what is being vaped varies across national surveys. Questions range from general wording, such as “Have you tried an e-cigarette?” to much more specific items, such as “Have you ever used an e-cigarette to inhale another drug or substance other than nicotine?” [21,24]. While some questions differentiate between nicotine and non-nicotine substances, few explicitly establish whether non-nicotine substances include cannabis or other substances. Although the ability of youth to accurately self-report nicotine content is unclear, the different types of vaping and terminologies used represent a challenge to measuring the prevalence of different forms of nicotine and cannabis use [12,25,26].

While the prevalence of e-cigarette use and cannabis vaping has been examined within individual countries, there is little data available to be able to directly compare between country differences among youth. The current study captured data from youth in Canada, England and the U.S., providing the unique opportunity for comparisons between these countries, where the regulatory frameworks for nicotine and cannabis products differ. With the focus on youth in Canada, England and the U.S., the purpose of the study was: (1) To assess the prevalence of various modes of nicotine and cannabis use, with a focus on vaping and smoking. (2) To examine the extent of overlap between vaping and smoking both cannabis and nicotine products. (3) To examine differences in patterns of use between youth in Canada, England and the U.S. (4) To examine the proportion of youth who may be incorrectly classified as ‘e-cigarette’ users when they had only vaped cannabis.