Given the recent legalization of cannabis in Canada, the 4 papers published in this issue addressing the risks associated with cannabis use are timely. These research papers provide further confirmation and elaboration of the known risks of harm, and further the evidence-base that informed Canada’s framework for legalization with strict regulation. Chiefly, we know that cannabis is not a “harm-free” substance and that use carries risk for some, especially those who may be vulnerable due to factors such as an earlier age of initiation and greater frequency of use, and because of the association between use and pre-existing or co-occurring mental illness. To this end, these studies and reviews reinforce recommendations for reducing the potential for harm found within Canada’s “Lower Risk Cannabis Use Guidelines”, recently updated and disseminated in advance of legalization.
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Hosseini and Oremus
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review the evidence on the relationship between age of cannabis initiation and psychosis—the mental health issue that has received the most attention. They also consider associations with depression and anxiety, which are equally important but feature less prominently in discussions of potential risks associated with cannabis use. This paper makes an important contribution to our knowledge about cannabis use and the age of onset of psychosis. They summarize evidence from cross-sectional studies that suggest that the risks of psychotic experiences and symptoms are greater among those who begin using cannabis earlier than age 14, well below the lowest age (18 years) possible in Canada’s Federal legislation. As the authors suggest, the associations between frequency of use and depression and anxiety are less clear; as seen through cohort and case-control studies, there is some evidence to suggest a positive association between anxiety and more intense or frequent cannabis use. Given the public and scientific debates that continue to intensify around the direction and causality of the relationship between adolescent cannabis use and psychosis in the context of legalization in North America,
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the authors’ conclusion that their review did not find evidence to support the claim that “early onset cannabis use by itself is sufficient to precipitate psychotic illness” (p 5) bears repeating.
Dugas et al.
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consider how a range of potential risk factors from longitudinal adolescent self-report data—including age and frequency of use—can be used to identify those at risk for potential harms associated with frequent (daily) use. That they cite the need for scientific consensus on the interactions between “frequency of use, dose, age of initiation, and psychosocial factors” (p 2) in order to better characterize adolescent pathways into problematic use is critical to consider in the post-legalization era. Dugas et al. also challenge typical assumptions around greater maternal education as a protective factor for negative cannabis use outcomes, as evidence from their cohort study suggests that a lower level of post-secondary education among mothers had a protective effect for cannabis use, as did being born outside of Canada. The results also provide evidence for moving away from the dominant approach of universal drug education interventions that provide adolescents with drug information. By illustrating how the potential for problematic, daily use by young people is tied to the co-occurrence of factors such as substance co-use, gender, family stress, and impulsivity, their paper lends support for new research on targeted or personality-typing interventions to prevent cannabis use, which is now underway in Canada and other contexts.
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The short report from Smith et al.
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provides a snapshot of how post-secondary students at one university are using cannabis for medical and non-medical purposes in the period immediately before legalization. In seeking to understand more about why and how young adults are using for medical reasons, this helps to fill a gap in our knowledge about young adult use in Canada. In their discussion, the authors seem to suggest that medical use by young adults may be harmful, mainly because the conditions they report using cannabis for are not encompassed in the College of Family Physicians of Canada’s prescribing guidelines, but also because 40% of those surveyed reported replacing using cannabis in place of another medicine. This neglects the potential benefits of substituting cannabis, which arguably has comparatively fewer known harms than drugs, such as benzodiazepines or opioids, which physicians commonly prescribe for the types of health issues survey respondents reported seeking to address with cannabis (i.e., sleep problems, pain, and anxiety).
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That 13.6% of respondents met the criteria for Cannabis Use Disorder (CUD) is of concern and may be a point of intervention; yet, this value still falls within the spectrum of what is known about the risk of CUD (as Dugas et al.
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highlight in their article, this is about 9% for lifetime users and rises to 17% for those who initiate use at an early age).
Finally, Halladay et al.
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explore the potential associations between sex differences, cannabis use, and mental health, drawing from cross-sectional survey data from the Canadian Community Health Survey. Their model produced the novel finding that women who use cannabis, even occasionally, may be at greater risk of psychological distress as compared with men, with an even stronger relationship present for women who report regular use. Likewise, their model showed a significant association between women’s use of cannabis and their reporting of suicidal thoughts or attempts. Much of the research on cannabis use to date (including work cited in the papers by Dugas et al., and Hosseini et al.) suggests that it is men who initiate earlier, have higher usage, and are at greater risk of problematic use and psychosis. This seemingly strong evidence in support of a gendered association is important to study further to tell us why women who use cannabis—even infrequently and at a much lower prevalence than men—may be at risk for more negative mental health symptoms than men.
These papers advance our understanding of the mental health risks associated with cannabis use in Canada but, in some ways, reflect a broader tendency within substance use research to focus only on the potential for negative health outcomes associated with legalization. For example, although these papers allude to the harms of cannabis becoming socially normalized, legalization may also lessen the pervasive stigma around cannabis use, allowing for greater disclosure about use and opportunities for dialogue between patients and their health care providers about how to reduce risks. If people, particularly young people, are reporting that they are using cannabis to improve quality of life and to ameliorate symptoms associated with poor mental health, then they should be treated with compassion and non-judgment, through a harm reduction approach.
