The Cannabis Act, which came into force in October 2018, outlines a legal framework for controlling the production, distribution, and possession of cannabis in Canada [1] . Two of its primary goals are to prevent youth from accessing cannabis and to protect public health and safety by allowing safe and legal access of nonmedical cannabis to adults. In Canada, the typical age of initiation of cannabis use is 14 years, with prevalence peaking among young adults aged 20 to 24 years [2–5]. According to the 2017 Canadian Cannabis Survey, past-year use of cannabis among Canadians aged 16 to 24 years was double that of Canadians older than 24 [6]. Cannabis use is higher among certain population subgroups such as young people who report poor school performance, early use of tobacco, alcohol, and other drugs, those fraternizing with drug-using peers, those experiencing a difficult family environment, those who report higher cannabis accessibility and availability of cannabis, and those who are high on sensation-seeking [7, 8].

Youth who initiate cannabis at an earlier age may be at greater risk of negative health and social outcomes than those that delay initiation [9]. Young Canadians report a variety of reasons for using cannabis, including identity formation, as a tool for social cohesion, boredom, relief of social anxiety, perceived acceptability, and lower perceived risk of harm than other substances [10–14]. However, early cannabis use has been associated with greater impairments in memory, cognition, academic performance, heightened risk for cannabis dependence, and other negative health endpoints than those who delay or refrain from use [15–17]. Other general health effects include the exacerbation of mental health disorders, respiratory symptoms, increased risk of motor vehicle accidents, and lower birthweight of infants whose mothers smoked cannabis [17]. The majority of health consequences related to first-hand cannabis use occur among individuals who are high frequency and high intensity users [9, 18, 19].

Most young Canadians report that regular cannabis use has health risks. For example, the 2016-17 Canadian Student Tobacco, Alcohol and Drugs Survey (CSTADS), a nationally representative survey of youth, found that while 9% of youth reported that there was “no risk” of harm associated with smoking cannabis on a regular basis, approximately half (54%) thought that smoking cannabis on a regular basis posed “great risk” [2]. Data suggest that most young Canadians are aware of specific potential consequences associated with use; however, they do not appear to have an understanding of practical issues such as how long impairment might persist [12]. Among the general population, three-quarters of young Canadians (75%) believe that cannabis affects driving, and approximately 1 in 5 (19%) report that it does not affect driving at all [6]. Young Canadians report taking solace in the fact that cannabis affects everyone differently. Focus groups have found that young people are indifferent to the consequences associated with use and selectively decide the harms that use may elicit based on personal experience or anecdotes from their peers [12]. Indeed, many young people perceive cannabis as “natural,” a “soft drug,” or “not really a drug at all” [11, 12]. Approximately 6 in 10 Canadians report that cannabis is more helpful than harmful to their mental and physical health [13].

To date, most studies have assessed risk perceptions for cannabis use in general, simply probing about whether individuals believe that cannabis carries a level or risk. Few studies have examined risk perceptions for different types of cannabis products (e.g. edibles, concentrates) or modes of administration. Understanding risk perceptions, as they vary across product and modes of administration is critical as they have differential impacts on the body. The pharmacological effects of cannabis vary depending on the concentrations of its primary active ingredient, THC (tetrahydrocannabinol, Δ⁹-THC), as well as whether products are smoked, vaped, or ingested orally or otherwise [20]. The THC content of cannabis has increased significantly over the past three decades in North American markets in its dried herbal form and has reached up to 80 to 90% in high potency products such as oils or waxes [21–23]. In general, frequent use of products containing higher THC concentrations significantly increases the risk of psychotic disorders, paranoia, marked effects on memory, and dependence [24–28]. Synthetic cannabis is the term given to mixtures of synthetic compounds marketed as “herbal” mixtures (e.g., Spice, K2m, Mamba, Afghan Incense) that activate cannabinoid receptors. They are the largest, fastest-growing, and most diversified new psychoactive substances which have been observed to precipitate acute psychotic symptoms, fatal poisonings, acute myocardial infarction, delusions, renal dysfunction, among other effects [29–31]. Synthetic cannabinoid use among youth is an emerging phenomenon in North America, approximately 3% of young Canadians in Grades 7 to 12 have reported its use, and 12% of their American counterparts have reported the same; the Canadian Centre for Substance Abuse identified this as a substance of concern as early as 2014 [2, 32, 33].

According to decades of substance use research, increased perceived riskiness and health knowledge influences rates of substance use and are generally associated with reductions in use initiation, increased engagement in health protective behaviors, and long-term abstinence [34–39]. Individuals who perceive a substance such as cannabis to be high risk are generally less likely to use it, and vice versa [34]. When young people are made aware that use behaviors are not normative and their misperceptions about how many of their peers actually use substances are corrected, substance use behaviors tend to decrease [40, 41]. However, existing work from US contexts that have legalized medical and/or nonmedical cannabis are less clear, and the relationship between perceived risk, health knowledge, and use behaviors remains poorly understood with respect to cannabis [42, 43].

Young people access health information from a variety of channels. Of these, online spaces represent credible sources of information for youth and young adults [44, 45]. A study by Lamy and colleagues demonstrates how social media platforms like Twitter are able to disseminate information about cannabis that describes it as “pure,” “clean,” and a “natural medicine ”[46]. Ouellette and colleagues describe how YouTube users are spreading information about cooking with cannabis, receiving collectively 15.6 million views though little is currently known regarding the basic effects these preparations may have or about users’ habits of ingesting edibles [47]. Work by Ramo and colleagues identified more than 700 smartphone apps related to cannabis and characterized them as likely vehicles for cannabis-related information and misinformation [48]. Overall, however, there is little population-level data on sources of health information on cannabis among young people. This is important given that Health Canada is reportedly spending $100M on cannabis education over 6 years and should consider competing sources of information known to be available that may dampen education efforts [49].

The present study examined young Canadians’ awareness of negative health effects, a proxy for knowledge, associated with cannabis use, perceptions of risk and harm associated with cannabis use, perceptions of relative risk to other substances or forms of administration (e.g., smoking, vaping, edibles), how these vary by use intensity (e.g., occasional vs. daily use), and how those perceptions were influenced by reported exposure to public health education around cannabis use.