Factors Associated with Initiating Cannabis Use After Legalization in Canada: A Cross-Sectional Study

Abstract

Background:

Cannabis use has increased since the Government of Canada legalized nonmedical use in October 2018. We investigated demographic factors associated with initiating cannabis use after legalization.

Materials and Methods:

We used data from the 2018 and 2019 National Cannabis Survey and constructed multivariable regression models. Respondents' data were weighted and bootstrapped. We report relative measures of association as adjusted odds ratios (ORs) and absolute measures of association as adjusted risk increases (RIs).

Results:

Among the 58,195 households surveyed, 28,566 provided complete data (49%) and our weighted analysis represented 27,904,258 Canadians aged ≥ 15 years. Approximately one in five Canadians endorsed use of cannabis (19.8%), predominantly for nonmedical (9.5%) or combined medical and nonmedical (5.8%) reasons. Those who initiated cannabis use in the past 3 months (1.9%) were more likely to be younger (25–34 years vs. ≥ 65 years; adjusted OR 1.7, 95% confidence interval [CI] 1.1–2.8; adjusted RI 1.1%, 95% CI 0.1–2.0%), endorse poor to fair versus good to excellent physical health (adjusted OR 2.0, 95% CI 1.3–3.1; adjusted RI 1.7%, 95% CI 0.3–3.1%), and reside outside of Quebec (adjusted OR 1.4, 95% CI 1.1–2.0; adjusted RI 0.1%, 95% CI 0.6–1.1%). The 1% of Canadians who endorsed initiating use of cannabis due to legalization were more likely to reside outside of Quebec (adjusted OR 1.9, 95% CI 1.1–3.2; adjusted RI 0.5%, 95% CI 0.2–0.9%).

Conclusion:

Canadians initiating cannabis use after nonmedical legalization were likely to be younger and endorse worse physical health, and half of those using cannabis reported therapeutic use. Stricter policies, lower social acceptance, and less availability of cannabis in Quebec appear to have curtailed initiation of use after legalization.

Introduction

Cannabis is the most widely used illicit substance in the world; nearly half of Canadians report having used cannabis at some time in their lives.¹ In an effort to promote responsible use, deter criminal activity, protect public health and safety, and reduce access to cannabis among youth, the Canadian federal government legalized possession, sale and use of cannabis for nonmedical purposes in October 2018.^1–4 Also in 2018, Statistics Canada launched the National Cannabis Survey (NCS), administered quarterly, to gather information on the impact of legalizing cannabis for nonmedical use.⁵ In 2019, the NCS found that more than 5.1 million Canadians (16.9% of the population) reported use of cannabis, an increase from 4.6 million (15.2%) just before legalization.⁶ Proportion of first-time users doubled from the first quarter of 2018 to the same period in 2019.⁷

The general public, on average, underestimates the harms associated with cannabis use.⁸ Early onset psychosis,^9–11 adverse respiratory effects,^12–14 dependence,¹⁵ impaired fetal development,^16–19 and increased risk of suicide, depression, and anxiety disorders^20,21 are among harms that have been associated with cannabis use. Given the potential for adverse effects, it would be desirable to identify individuals at greater risk of initiating use to target public health messaging. The objective of our study was to explore demographic factors associated with initiating cannabis use after legalization for nonmedical use in Canada.

Materials and Methods

This report adheres to the Strengthening the Reporting of Observational Studies in Epidemiology guideline.²²

Study design and setting

This was a cross-sectional study involving analysis of data from the NCS master file collected after legalization of nonmedical use of cannabis: the fourth wave of 2018 and all four waves in 2019. The NCS was developed by Statistics Canada in consultation with the Public Health Agency of Canada, the Department of Justice Canada, and Public Safety Canada. Participation in the NCS is voluntary and data are acquired through an electronic questionnaire or computer-assisted telephone interview. Our study population consisted of noninstitutionalized Canadians aged ≥15 years who resided in Canada's 10 provinces or 3 territorial capital cities. The sampling method was a two-stage simple random sample of dwellings and people stratified by province or territory, which aimed to represent the Canadian population.²³

A total of 58,195 households were selected to receive the fourth NCS wave in 2018 and all four waves in 2019. Response rates were 50.4% (wave 4, 2018), 50.6% (wave 1, 2019), 46.9% (wave 2, 2019), 50.9% (wave 3, 2019), and 47.2% (wave 4, 2019). A total of 28,566 respondents (49.1%) replied to the questionnaire, among whom 23,757 (83.2%) provided complete surveys for Q10 and 23,013 (80.1%) for Q15 that we included in our multivariable logistic regression analyses. Our final sample for analysis considered all respondents, including those who were already using cannabis. We accessed NCS data through the Statistics Canada Research Data Centre at McMaster University.²⁴

Measures

We used two items in the NCS questionnaire as our outcomes of interest for our regression models. In the first model, we considered “Did you start using cannabis in the past three months?” as our dependent variable and in the second model, we considered “Did you use or try cannabis for the first time because it is now legal?” as our dependent variable. For both dependent variables the response options were (1) yes, (2) no, (3) valid skip as use of cannabis was endorsed in a prior question, and (4) not stated. For the purposes of analysis, we collapsed response options into “yes” and “no” (response options 2 and 3) and considered “not stated” as missing data (Supplementary Table S1).

The NCS data set included information on age, gender, marital status, self-reported physical and mental health, main activity during the previous week (i.e., occupation), education and income level, route of cannabis administration, and province of residence. Categories for variables were collapsed in some cases to ensure adequate cross tabulation counts and simplify analysis and interpretation by converting categorical to binary variables (Supplementary Table S1). As the NCS categories of male and female for gender are commonly understood as the sex of a person, we have interpreted them as such in our study.²⁵

Statistical analysis

We pooled data from the five independent NCS waves for our analysis. We used descriptive statistics to summarize demographic data as percentages and 95% confidence intervals (CIs) using pairwise deletion for missing data (i.e., reporting all cases for which we had data). We constructed unadjusted (univariable) and adjusted (multivariable) logistic regression models to explore factors associated with (1) initiating cannabis use in the past 3 months (Model 1), and (2) initiating cannabis use because of legalization (Model 2).

Our independent variables included age, sex, marital status, physical and mental health status, occupation, education, and income, as previous studies have reported associations with these factors and cannabis use.^26–29 We also included whether respondents resided in Quebec in our models, as this province enacted stringent policies to access nonmedicinal cannabis and cannabis use is less socially acceptable compared with the rest of Canada.³⁰ All independent factors were included in both adjusted models, whether they were statistically significant in univariable analysis or not. Post hoc, we also entered interaction terms between age and physical and mental health and between sex and physical and mental health in our regression models.

Furthermore, we ran a post hoc analysis exploring the impact of splitting the 15–24 age category into older adolescents (15–18) and young adults (19–25); however, neither group showed a significant association with either of our dependent variables and so we presented the collapsed age category in our reported models to increase the cell count and improve precision. We adjusted our regression models for survey wave. As required by Statistics Canada, we applied bootstrap weights to convert unweighted frequencies to represent the Canadian household population and adjust for nonresponse bias in the survey sampling design. We excluded missing data from our multivariable regression analyses using listwise deletion.

Results from our regression models are presented as odds ratios (OR) with 95% CIs. All analysis were two-tailed with a statistical significance level of p≤0.05. We applied the likelihood ratio test to determine regression model fit and the Hosmer–Lemeshow test to assess the goodness of fit of our adjusted models.³¹ To optimize interpretability, we calculated the adjusted risk increase (RI) for all associations in our adjusted models.³² We considered the risk difference large when the baseline risk was doubled (OR ≥2) or reduced by half (OR ≤0.5). All analyses were performed using Stata (StataCorp., Release 15.1. College Station, TX).

Ethics approval

As per Article 2.2(a) of the Tri-Council Policy Statement: Ethical Conduct for Research Involving Humans, research is exempt from research ethics board review if it relies exclusively on publicly available information that is legally accessible to the public.³³ Our results were reviewed by an analyst at the Statistics Canada Research Data Centre at McMaster University before release to ensure that the confidentiality of survey respondents' information was respected.

Results

There was an equal representation of males and females among our survey respondents, most were married, employed or looking for work, and the large majority reported good to excellent mental and physical health. Twenty percent of respondents reported use of cannabis for the past 3 months, with half of them endorsing nonmedical use only and the remainder split between medical use only or dual use (medical and nonmedical) (Table 1).

Table 1.

Respondent Characteristics (Weighted n=27,904,258)

Characteristic	Percentage (95% CI)
Age
15–24	12.7 (12.1–13.3)
25–34	18.4 (17.8–19.0)
35–44	16.1 (16.0–16.1)
45–64	32.2 (32.1–32.4)
≥65	20.6 (20.6–20.7)
Sex
Female	50.9 (50.8–51.0)
Male	49.1 (49.0–49.2)
Marital status
Married	61.7 (61.0–62.4)
Single	38.3 (37.6–39.0)
Physical health
Good to excellent	90.3 (89.8–90.8)
Fair to poor	9.7 (9.2–10.2)
Mental health
Good to excellent	93.5 (93.0–93.9)
Fair to poor	6.5 (6.1–7.0)
Daily activity
Employed/looking for job	54.7 (53.9–55.5)
Student	8.1 (7.5–8.6)
Caregiving/housework	8.2 (7.7–8.6)
Retired/long-term illness	22.4 (22.0–22.9)
Other	6.6 (6.2–7.1)
Formal education
High school diploma or lower	33.8 (33.0–34.7)
College degree and higher	66.1 (65.3–67.0)
Income
<$40,000	21.3 (20.6–22.0)
$40,000 to $79,999	30.9 (30.0–31.7)
≥$80,000	47.9 (47.0–48.8)
Reason(s) for cannabis use
Nonuser	80.2 (79.5–81.0)
Medical use only	4.4 (4.1–4.8)
Nonmedical use only	9.5 (9.0–10.1)
Medical and nonmedical use	5.8 (5.3–6.4)
Province or territory capital city of residence, grouped
Quebec	23.0 (22.9–23.0)
Territorial capital cities	0.4 (0.4–0.4)
Atlantic provinces	6.5 (6.5–6.5)
Ontario	39.4 (39.4–39.4)
Manitoba	3.4 (3.4–3.4)
Saskatchewan	2.9 (2.9–2.9)
Alberta	11.5 (11.5–11.5)
British Columbia	13.3 (13.3–13.3)
Survey wave
Wave 4, 2018	19.9 (19.8–19.9)
Wave 1, 2019	19.9 (19.9–19.9)
Wave 2, 2019	20.0 (20.0–20.1)
Wave 3, 2019	20.1 (20.1–20.1)
Wave 4, 2019	20.2 (20.1–20.2)

CIs, confidence intervals.

Overall, 1.9% of respondents reported they initiated use of cannabis in the past 3 months. Univariate analysis showed significant association between starting use of cannabis in the past 3 months with younger age (15–34 years vs. ≥65 years), being single versus married, reporting poor to fair physical health, reporting poor to fair mental health, and residing outside of Quebec; being retired or reporting long-term illness versus being employed reduced the odds of initiating cannabis use in the past 3 months.

In our adjusted model (Model 1), younger age (25–34 years vs. ≥65 years; adjusted OR 1.7, 95% CI 1.1–2.8; adjusted RI 1.1%, 95% CI 0.1–2.0%), endorsing poor to fair versus good to excellent physical health (adjusted OR 2.0, 95% CI 1.3–3.1; adjusted RI 1.7%, 95% CI 0.3–3.1%), and residing outside of Quebec (adjusted OR 1.4, 95% CI 1.06–2.0; adjusted RI 0.6%, 95% CI 0–1.1%) were associated with recent initiation of cannabis use (Table 2). The Hosmer–Lemeshow (p=0.6) and likelihood ratio (p<0.05) tests suggested a good fit for our adjusted model.

Table 2.

Factors Associated with Initiating Cannabis Use in the Past 3 Months (Weighted n=27,906,388)

Predictor	Unadjusted OR (95% CI)	Adjusted OR (95% CI)	p	Adjusted risk increase, % (95% CI)
Age (years)
65≤	Ref
15 to 24	1.7 (1.1 to 2.7)^*	1.5 (0.8 to 2.9)	0.26	0.7 (−0.6 to 1.9)
25 to 34	1.9 (1.3 to 2.8)^*	1.7 (1.1 to 2.8)	0.03	1.1 (0.1 to 2.0)
35 to 44	1.4 (1.0 to 2.1)	1.3 (0.8 to 2.1)	0.31	0.4 (−0.4 to 1.2)
45 to 64	1.3 (0.9 to 1.8)	1.2 (0.8 to 1.8)	0.43	0.3 (−0.4 to 0.9)
Sex
Female	Ref
Male	1.1 (0.9 to 1.4)	1.1 (0.9 to 1.5)	0.38	0.2 (−0.3 to 0.7)
Marital status
Married	Ref
Single	1.3 (1.0 to 1.7)	1.3 (0.9 to 1.7)	0.13	0.5 (−0.2 to 1.1)
Physical health
Good to excellent	Ref
Fair to poor	2.1 (1.5 to 2.8)	2.0 (1.3 to 3.1)	0.002	1.7 (0.3 to 3.1)
Mental health
Good to excellent	Ref
Fair to poor	2.0 (1.4 to 2.9)	1.3 (0.8 to 2.1)	0.30	0.6 (−0.6 to 1.7)
Daily activity
Employed/looking for work	Ref
Student	1.0 (0.6 to 1.7)	0.9 (0.4 to 1.8)	0.74	−0.2 (−1.5 to 1.0)
Caregiving/housework	1.1 (0.7 to 1.7)	1.1 (0.7 to 1.9)	0.47	0.3 (−0.9 to 1.4)
Retired/long-term illness	0.7 (0.5 to 0.9)	0.8 (0.5 to 1.2)	0.25	−0.4 (−1.1 to 0.3)
Other	0.8 (0.5 to 1.2)	0.7 (0.4 to 1.2)	0.20	−0.6 (−1.4 to 0.2)
Formal education
High school diploma or less	Ref.
College and higher	1.0 (0.8 to 1.3)	1.0 (0.7 to 1.4)	0.98	0.0 (−0.6 to 0.6)
Income
<$40,000	Ref
$40,000 to $79,999	1.0 (0.7 to 1.4)	1.1 (0.7 to 1.6)	0.79	0.1 (−0.6 to 0.8)
≥$80,000	1.1 (0.8 to 1.6)	1.2 (0.8 to 1.7)	0.32	0.3 (−0.3 to 1.0)
Residence
Quebec	Ref
Outside of Quebec	1.5 (1.0 to 2.2)	1.4 (1.1 to 2.0)	0.01	0.6 (0.0 to 1.1)

Bold numbers had significant association, p-value ≤0.05.

OR, odds ratios.

One percent of our respondents reported they initiated cannabis use because of legalization.

Univariate analysis showed that all younger age categories versus ≥65 years old, endorsing poor to fair mental health, and residing outside of Quebec were associated with starting cannabis use due to legalization; being retired or reporting long-term illness was associated with reduced odds of initiating cannabis use after legalization. In our adjusted model (Model 2), only residing outside of Quebec was associated with starting cannabis use because of legalization (adjusted OR 1.9, 95% CI 1.1–3.2: adjusted RI 0.5%, 95% CI 0.2–0.9%) (Table 3). Both the Hosmer–Lemeshow (p=0.5) and likelihood ratio (p<0.05) tests suggested a good fit of our adjusted model. We did not find any significant interactions between age and sex and physical and mental health in either of our regression models.

Table 3.

Factors Associated with Initiating Cannabis Use Due to Legalization (Weighted n=27,904,258)

Predictor	Unadjusted OR (95% CI)	Adjusted OR (95% CI)	p	Adjusted risk increase, % (95% CI)
Age (years)
≥65	Ref.
15 to 24	2.6 (1.4 to 4.9)^*	1.5 (0.6 to 3.5)	0.34	0.4 (−0.4 to 1.1)
25 to 34	2.8 (1.6 to 4.9)	1.8 (0.9 to 3.6)	0.10	0.6 (−0.1 to 1.2)
35 to 44	1.7 (1.0 to 2.9)	1.1 (0.5 to 2.1)	0.88	0.0 (−0.5 to 0.5)
45 to 64	1.9 (1.2 to 3.2)	1.4 (0.8 to 2.7)	0.25	0.3 (−0.2 to 0.8)
Sex
Female	Ref.
Male	1.0 (0.7 to 1.5)	1.0 (0.7 to 1.5)	0.85	0.0 (−0.3 to 0.4)
Marital status
Married	Ref.
Single	1.2 (0.9 to 1.8)	1.1 (0.7 to 1.8)	0.61	0.1 (−0.4 to 0.6)
Physical health
Good to excellent	Ref.
Fair to poor	1.5 (1.0 to 1,2.2)	1.3 (0.8 to 2.3)	0.32	0.3 (−0.4 to 1.0)
Mental health
Good to excellent	Ref.
Fair to poor	2.3 (1.4 to 3.7)	1.8 (1.0 to 3.4)	0.07	0.8 (−0.3 to 1.8)
Daily activity
Employed/looking for work	Ref.
Student	1.2 (0.6 to 2.5)	1.1 (0.5 to 2.5)	0.81	0.1 (−0.7 to 1.0)
Caregiving/housework	1.2 (0.6 to 2.6)	1.3 (0.6 to 2.8)	0.75	0.3 (−0.6 to 1.2)
Retired/long-term illness	0.5 (0.3 to 0.8)	0.7 (0.4 to 1.2)	0.21	−0.3 (−0.8 to 0.1)
Other	0.6 (0.3 to 1.3)	0.5 (0.2 to 1.2)	0.11	−0.6 (−1.0 to −0.1)
Education
High school diploma or lower	Ref.
College and higher	1.0 (0.7 to 1.5)	1.0 (0.7 to 1.4)	0.83	−0.1 (−0.4 to 0.3)
Income
<$40,000	Ref.
$40,000 to $79,999	1.1 (0.7 to 1.9)	1.1 (0.6 to 2.0)	0.70	0.1 (−0.4 to 0.6)
≥$80,000	1.2 (0.8 to 2.0)	1.2 (0.7 to 2.0)	0.55	0.2 (−0.4 to 0.7)
Residence
Quebec	Ref.
Outside of Quebec	2.0 (1.1 to 3.5)	1.9 (1.1 to 3.2)	0.03	0.5 (0.2 to 0.9)

Bold numbers had significant association, p-value ≤0.05.

Discussion

After legalization of nonmedical cannabis, ∼1 in 50 Canadians initiated use and ∼1 in 100 attributed their decision to start using cannabis to legalization. Thus, it seems that the illegality of cannabis did deter a minority of Canadians from using cannabis. Most used cannabis for nonmedical purposes; however, approximately half endorsed either medical or dual (medical and nonmedical) use. Respondents endorsing fair to poor physical health were more likely to start use of cannabis in the past 3 months, and initiation of cannabis use in the past 3 months or due to legalization was less likely in Quebec versus the rest of Canada.

An analysis of NCS data just before legalization of nonmedical cannabis found that 8.3% of Canadians reported their intention to try cannabis after legalization.² Our analysis of actual usage data found that only 1.9% of Canadians did so, emphasizing that intentions do not necessarily translate into changes in behavior. Our finding that endorsing worse physical health was associated with initiating cannabis use, and 4% of respondents reported using cannabis for therapeutic reasons, and 6% for both medical and nonmedical purposes, reinforces the importance of providing guidance regarding evidence-based therapeutic indications for cannabis. In 2020, ∼420,000 Canadians were authorized by Health Canada to acquire cannabis for medical purposes.³⁴ However, the 2019 Canadian Cannabis Survey found that only 24% of those who used cannabis for medical purposes had authorization from a health care professional.³⁵ Our finding that younger respondents were more likely to initiate cannabis use is consistent with prior Canadian studies.^36,37

Respondents who resided in Quebec were less likely to initiate cannabis use in the past 3 months or because of legalization, and this may be associated with cultural views toward cannabis, policy decisions, and availability in this province.³⁶ Specifically, home cultivation of cannabis is prohibited,³⁸ and Quebec has fewer cannabis stores and license producers per capita than other provinces in Canada.^39,40 Our findings suggest that province-specific policies regarding access to cannabis may deter use. On January 1, 2020, after our data were collected, Quebec raised the minimum legal age for purchasing and consuming cannabis to 21 years,⁴¹ which contrasts with 18 years in Alberta and 19 years for the rest of Canada,⁴² which may further affect use.

Our study does have limitations. More than half of eligible households approached did not complete the NCS, and it is possible that our respondents may have under-reported use of cannabis; however, our data were collected after legalization, which should reduce concerns about declaring cannabis use and prior studies have found data on self-reported drug use to be reliable.^43,44 The NCS uses single-item low-resolution questions for assessing physical and mental health rather than psychometrically validated tools. Furthermore, the NCS does not collect information on people in institutions and our findings may not be generalizable to this population.

Conclusion

After legalization of nonmedical cannabis, 1 in 50 Canadians initiated use and 1 in 100 attributed their decision to start using cannabis to legalization. Canadians initiating cannabis use were likely to be younger and endorse worse physical health, and half of those using cannabis reported use for therapeutic purposes. Stricter policies implemented in Quebec, lower social acceptability, and reduced availability of cannabis compared with the rest of Canada, appear to have curtailed initiation of use after legalization.

Footnotes

Authors' Contributions

Each author contributed substantially to the conception and design of the article. V.A. analyzed the data and drafted the initial article. Each author revised the article critically for important intellectual content, gave final approval of the version to be published, and agreed to be accountable for all aspects of the study.

Acknowledgments

The authors thank Drs. Li Wang and Peter Kitchen (Statistics Canada Research Data Centre at McMaster University). This analysis was conducted at the Statistics Canada Research Data Centre at McMaster University, which is part of the Canadian Research Data Centre Network. The services and activities provided by the Statistics Canada Research Data Centre at McMaster University are made possible by the financial or in-kind support of the Social Sciences and Humanities Research Council, the Canadian Institutes of Health Research, Statistics Canada and McMaster University.

Data Sharing

The 2018 and 2019 NCS master file can be accessed through a Research Data Centre. The analysis code can be accessed by contacting the corresponding author.

Author Disclosure Statement

No competing financial interests exist.

Funding Information

This was an unfunded study. Dr. Ashoorion was supported by a Michael G. DeGroote Centre for Medicinal Cannabis Research postdoctoral fellowship.

Supplementary Material

Abbreviations Used

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