Use of Cannabis for Harm Reduction Among People at High Risk for Overdose in Vancouver, Canada (2016–2018)

Abstract

Objectives. To characterize the prevalence and reasons for the use of cannabis as a strategy to reduce the harms arising from other substances.

Methods. We drew data about recent cannabis use and intentions from 3 prospective cohort studies of marginalized people who use drugs based in Vancouver, Canada, from June 2016 to May 2018. The primary outcome was “use of cannabis for harm reduction,” defined as using cannabis for substitution for licit or illicit substances such as heroin or other opioids, cocaine, methamphetamine, or alcohol; treating withdrawal; or coming down off other drugs.

Results. Approximately 1 in 4 participants reported using cannabis for harm reduction at least once during the study period. The most frequent reasons included substituting for stimulants (50%) and substituting for illicit opioids (31%).

Conclusions. The use of cannabis for harm reduction is a common strategy among people who use drugs in our setting. Further research into the factors associated with this strategy is needed. Better characterization of the risks and benefits of substitution strategies, including for opioids and stimulants, may prompt new treatment options for PWUD.

Globally, cannabis is the most commonly used drug, with 192 million people using it in 2018.¹ Research surrounding cannabis has predominantly focused on its potential harms.² Recently, interest in the therapeutic potential of cannabis has emerged, including its utility as a harm-reduction strategy, by using cannabis to reduce, eliminate, or substitute for other psychoactive substances.³

Previous studies have examined the therapeutic potential of cannabis substitution for specific substances^4,5; this study aimed to evaluate the prevalence of and reasons for using cannabis as a harm-reduction strategy among the broader population of people who use drugs (PWUD) during a community-wide opioid crisis.

METHODS

We drew data from 3 ongoing prospective cohort studies involving PWUD in Vancouver, Canada.⁵ The Vancouver Injection Drug Users Study (VIDUS) consists of HIV-negative adults (aged ≥ 18 years) who injected drugs in the month before enrollment; the AIDS Care Cohort to Evaluate exposure to Survival Services (ACCESS) includes HIV-positive adults who used illicit drugs; and the At-Risk Youth Study (ARYS), includes street-involved youths aged 14 to 26 years who used illicit drugs. Participants were recruited through community-based outreach, including in Vancouver’s Downtown Eastside and Downtown South—areas with prevalent polysubstance use, marginalization, and an ongoing community-wide opioid overdose crisis.

After participants provide written informed consent, they complete interview-administered questionnaires at baseline and at follow-up visits every 6 months. These questionnaires gather data on demographics, patterns of drug use, use of health care and social services, and other health-related factors. Nurses also conduct testing for HIV and hepatitis C serostatus, as appropriate. Participants receive a $40 honorarium at each study visit.

We restricted the study sample to participants with at least 1 follow-up interview between June 2016 and May 2018, as questions about specific uses of cannabis were added in June 2016.

Measures

Participants who reported using cannabis within the last 6 months were asked the reason for its use, including intoxication, pain management, nausea, mental health, or substance-use related challenges. Use of cannabis for harm reduction was defined by self-reported use of cannabis for substitution for licit or illicit substances, such as opioids, stimulants, or alcohol; treating withdrawal; or coming down off other drugs. While “harm reduction” is broad and can include formal policies and programs, in this study, the term describes self-directed practices to moderate the use of other substances. Participants reporting no cannabis use in the 6 months before the study visit were categorized as not having used cannabis for harm reduction. This measure was developed and refined by investigators in consultation with study participants and front-line research staff.⁶

Analyses

We characterized the analytic sample using descriptive statistics based on baseline data. We analyzed frequencies of the reasons for using cannabis for harm reduction. Participants could give more than 1 reason for using cannabis for harm reduction, resulting in more observations than participants.

RESULTS

The analysis included 1936 participants who contributed a median of 3 observations (interquartile range [IQR] = 2–4), for a total of 5706 observations. The median age at the earliest interview was 42 (IQR = 29–53) years; 1201 participants (62%) reported male gender; and 945 (49%) reported White race. The most common illicit drug used daily was cannabis (n = 547; 28%), followed by heroin via injection (n = 404; 21%) and crystal methamphetamine via any route (n = 331; 17%). Nearly half of the study sample (n = 838; 43%) were not enrolled in any form of treatment of substance use disorders.

Over the study period, 1281 (66%) participants used cannabis at least once. There were 425 participants who reported using cannabis for harm reduction (22% of total participants and 33% among participants who used cannabis at least once). There were 551 observations recording cannabis use for harm reduction, representing 10% of all interviews and 17% of interviews among people who used cannabis at least once.

As shown in Figure 1, the most frequent uses of cannabis for harm reduction were substituting for stimulants (e.g., cocaine, methamphetamine; n = 274; 50%) and for illicit opioids (n = 171; 31%). Other reasons included coming off of other drugs (n = 137; 25%), substitution for licit substances (n = 85; 15%), and treatment of withdrawal (n = 84; 15%).

FIGURE 1—

Reported Reasons for Using Cannabis for Harm Reduction: Vancouver, British Columbia, Canada, June 2016 to May 2018

Note. The sample size was 551 observations. Participants (n = 425) were permitted to provide more than 1 reason for using cannabis for harm reduction, resulting in a greater number of observations than participants.

DISCUSSION

Among our sample of PWUD in Vancouver, use of cannabis for harm reduction was a common strategy, reported by approximately 1 in 4 respondents at least once during the study period. The most frequent reasons included substitution for stimulants or for illicit opioids.

Treatments for stimulant-use disorders have been found to be of limited efficacy.⁷ This may partially explain the high prevalence of cannabis substitution for stimulants in our study. Substitution may directly decrease substance use, as suggested by an observational study in our setting demonstrating that intentional cannabis use preceded reduced frequency of crack cocaine use.⁵ While substitution may not always be an intentional attempt to lessen stimulant use, it may have indirect positive effects, including reduced cravings and less aggressive behavior.⁸ Further exploration of cannabis substitution among people who use stimulants may help inform harm-reduction strategies in this population, who are at high risk of health complications, and also prompt the evaluation of new treatment options for stimulant-use disorders.

In light of ongoing opioid overdose crises, substitution of cannabis for opioids is an area under much research and debate.³ A recent clinical trial demonstrated that cannabidiol, a nonintoxicating component in some cannabis preparations, decreased opioid cravings and drug-related anxiety.⁴ Similarly, initial population-based research showed a negative association between jurisdictions with access to medical or recreational cannabis and opioid-related mortality.⁹ However, these findings were contested by a more recent study,¹⁰ illustrating the need for further research to understand whether cannabis may have a role in addressing the opioid crisis.

This study had a number of limitations. Our sample of PWUD may not be representative of PWUD in other settings, thus limiting generalizability. This study also relied on self-report, which may affect data collected on illicit drug use, though previous studies have found that survey data from PWUD are reliable and valid.¹¹ In addition, this study did not explicitly incorporate participants’ voices or examine factors associated with using cannabis for harm reduction. However, previous quantitative and qualitative studies in our setting indicate that some people who use cannabis with therapeutic intent (including for harm reduction), intentionally incorporate cannabis into daily routines and obtain cannabis from reliable sources.^6,12 As described by 1 individual,

I don’t wanna [inject meth and heroin] anymore. As soon as I think about it—like, right now, I’m kind of getting a craving for it. But right after [this interview], I’m not gonna go out and pick any up, I’m gonna go to my dispensary and pick up a joint and I’ll be all fine.¹²

PUBLIC HEALTH IMPLICATIONS

Findings from this study suggest that self-medication with cannabis may be an intentional and common strategy by which some PWUD manage their substance use. In particular, individuals may use cannabis to substitute for opioids or stimulants. Further research may allow for a better understanding of circumstances under which individuals choose this harm-reduction strategy. These insights may contribute to public health–based strategies to address drug-related harms or regulate licit medical and recreational cannabis systems.