Implications of Cannabis Legalization on Substance-Related Benefits and Harms for People Who Use Opioids: A Canadian Perspective

Background

In 2018, Canada gained massive international media attention with the Cannabis Act, becoming only the second country to legalize the recreational consumption of cannabis after Uruguay. ¹ The primary goals of the Act were twofold: reducing cannabis use and cannabis-related criminalization among youth and eradicating the unregulated cannabis market. The effects have been widespread, with early data suggesting up to 65% reduced criminal convictions for cannabis-related crimes among youth, ² $2.6 billion in revenue from cannabis-related sales, ³ and drastic increases in legal dispensaries^4,5 since the Act was implemented. However, the implications of cannabis legalization on substance-related harms and benefits for people who use unregulated drugs (PWUDs), particularly opioids, remain unclear. ⁶

Changes in Cannabis-Related Metrics Postlegalization

Although there is ongoing global disagreement on the risk–benefit profile of cannabis with increasing legalization in many parts of the world, ⁷ the evidence of rising rates of cannabis use postlegalization has been consistent. For example, the most recent national surveys indicate that 27% of Canadian adults use cannabis annually, ⁸ representing a 5% point increase since 2017 and a 22% point increase since the first Canadian cannabis survey in 1985. However, available public health data on changes in the prevalence of cannabis-related harms, such as cannabis-related traffic accidents^9,10 and emergency department visits for cannabis intoxication,^11–14 have been inconsistent.

In addition, although cannabis legalization may have unique implications around substance-related harms and benefits for PWUDs, few studies have specifically evaluated these issues. For example, no Canadian studies have evaluated the relationship between cannabis use and opioid overdose fatalities, polysubstance use,^15,16 or the development of other substance use disorders. Consequently, extant Canadian policy decisions have not readily considered the harm reduction potential of cannabis among PWUDs. These concerns indicate the need for a shared conceptual model to evaluate cannabis legalization's unique harms and benefits within different populations, including PWUDs.

Impact of Cannabis Legalization on Opioid-Related Metrics

Although Canada did not legalize cannabis as an intervention in the opioid overdose crisis, there is rising interest in the therapeutic potential of cannabis for opioid-related harms. ¹⁷ To that end, appraising the benefits and harms of cannabis in reducing opioid-related harms, such as opioid overdose mortality rates, has become one area of research interest, particularly in the United States. For example, ecological studies have indicated lower state-level opioid overdose mortality rates in areas with medical cannabis legalization in the United States between 1999 and 2010. ¹⁸ However, the association reversed direction from −21% to +24% when the analyses were extended to 2017. ¹⁹ These conflicting reports highlight the danger of over-reliance on ecological studies and posit the need for higher quality studies.

Canadian Research Involving Cannabis Use Among People Who Use Opioids

Although no published studies have repeated these analyses in a Canadian setting, observational data suggest that there may be a beneficial association between cannabis use and several proximal risk factors for opioid overdose among PWUDs, including less frequent daily injection of unregulated opioids,^16,20 reduced fentanyl exposure among people on opioid agonist therapy, ²¹ and improved retention in opioid agonist therapy among daily cannabis users.^22–24 The available data also emphasize the importance of considering the context of cannabis use, such as distinguishing medical from recreational use.

For example, the effects of cannabis on PWUDs with chronic pain while tapering off opioids differ across medicinal and recreational (or therapeutic and nontherapeutic) intentions.^15,25 Yet, these findings do not necessarily translate to lower overdose rates. Ultimately, although cannabis use may mitigate the risk of opioid overdose for some individuals, it is unlikely to shift the direction of the opioid overdose crisis overall considerably. Consequently, the available literature on the impact of cannabis use among PWUDs suggests that rather than evaluating cannabis use on a large scale, we should determine how and for whom cannabis might benefit from an overdose prevention perspective.

Cannabis Use Disorder/Addiction

Although cannabis carries fewer inherent risks than opioids, particularly fatal overdose, it is neither risk-free nor a panacea. ²⁶ Yet, other cannabis-related risks, such as the development of cannabis use disorder (CUD), have also not been studied postlegalization in PWUDs. According to prelegalization data, ∼34% and 27% of individuals who use cannabis will develop CUD based on DSM-IV ²⁷ and DSM-5 criteria, ²⁸ respectively. Although CUD is qualitatively different from opioid use disorder (OUD) (i.e., it is often less intense and not directly life threatening), it can still lead to significant impairment. ²⁹

The potential for the under-recognition of CUD postlegalization is multifactorial. First, the accurate differentiation of cannabis use from CUD can be difficult and, consequently, difficulties around proper diagnosis likely lead to under-reporting of CUD. Second, unlike alcohol, opioids, or stimulants, the effects of cannabis are often far more subtle; this subtlety might also contribute to reduced recognition that someone has CUD and leads to diminished help seeking by people with CUD.

Third, the absence of evidence-based pharmacological treatments for CUD also contributes to decreased incentivizes to label cannabis use as CUD and reduces the likelihood that someone may present for a diagnostic assessment. ³⁰ Finally, cannabis use may be minimized among PWUDs who use multiple other substances with higher immediate risks. Consequently, recognition and treatment of CUD may not be a priority for clinicians working with PWUDs.

Challenges in Measuring the Impact of the Legalization of Cannabis

Although we have measures on the uptake of cannabis in the general population, clearly detailed data on more nuanced cannabis-related harms are lacking. Furthermore, there is very limited data on the uptake of cannabis among PWUDs, and only a small percentage is likely to use legal cannabis. However, even if these estimates could be specifically quantified, it is unclear how we could incorporate these findings into existing policy due to the lack of a shared conceptual model to evaluate the impacts and effects of cannabis legalization. To make matters more complicated, how do we compare these harms with the potential reduction in opioid use or reduction in rates of OUD that might stem from cannabis use for some individuals?

Furthermore, how do we scale this up to local, regional, provincial, or national use? These challenges suggest that evaluation frameworks involving substances are not necessarily about substance use but rather substance-related harms. However, measuring harm is hard, and measuring prevented harm is even harder. Ultimately, this points to the value and need for more nuanced ways of measuring the unintended and intended consequences of cannabis legalization rather than simple dichotomous assessments of policy as “good” or “bad.”

Future Directions and Conclusions

Largely, the available evidence evaluating the impact of cannabis legalization on PWUDs—and other populations—has relied upon ecological or observational findings. Although these kinds of studies provide many signals suggestive of benefit, the limited generalizability of these findings suggests a need to augment the evidence with higher quality studies, especially given the huge interest from the affected community, lay audience, policymakers, and clinicians.^31,32 Furthermore, with rising rates of cannabis use among Canadians, there is also a need to develop a balanced perspective considering legalization's harms and benefits.

In this regard, the implications of legalization are particularly nuanced when considering the unique situation involving PWUDs. Therefore, examining the impact of cannabis use on PWUDs should be a research priority in determining whether cannabis legalization can reduce drug-related harms (e.g., cannabis-related hospitalizations, CUD, quality of life, functional status, and opioid-related outcomes), and if so, which subpopulations might specifically benefit the most.