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Cannabis Use and Concern Among Clients Seeking Substance Misuse Treatment: Demographics, Comorbidities, and Service Utilization Patterns Pre-Legalization (2012–2018)

Williamson, Nicola MSc1,2; Hathaway, Josh MSc3,4; Jahrig, Jesse MSc4; Vik, Shelly PhD4,5; Rittenbach, Katherine PhD1,2,6

Author Information
The Canadian Journal of Addiction: March 2022 - Volume 13 - Issue 1 - p 19-26
doi: 10.1097/CXA.0000000000000136



Worldwide, cannabis is one of the most widely used nonmedical substances, with only alcohol and tobacco use more commonly reported.1,2 In 2017, the World Health Organization reported that 188 million individuals use cannabis globally. In Canada, cannabis for medical use was legalized in July 2001 and plans to legalize nonmedical use were announced in April 2016.3 In 2017, 4.4 million Canadians reported using cannabis in the past year, an increase of 40% from 2013 and 12% from 2015.4 Legalization discussions may have played a role in this reported increase due to changes in risk perceptions or reduced stigma following national dialogue about nonmedical legalization.5,6 Cannabis was eventually legalized for nonmedical use in Canada on October 17, 2018.7

The legalization of cannabis in Canada was controversial, with concerns raised about the impact of nonmedical legalization on health.8,9 Many of these concerns centered around the impact of legalization on mental health, in particular psychotic illnesses which have been associated with cannabis use.10,11 Heavy cannabis use in adolescence is associated with increased risk of psychosis in adulthood, an earlier onset of psychotic symptoms, and increased risk of relapse and psychiatric admission in those with a preexisting psychotic disorder.8,12–14 Cannabis is thought to adversely impact mental health conditions outside of psychosis with some evidence suggesting an increased risk of suicide, suicidal ideation, depression, and anxiety.9,15,16

Alongside concerns about the impact on mental health, are concerns about the impact of cannabis dependence on healthcare utilization. Research in other jurisdictions found legalization of medical cannabis use coincided with increased cannabis use and cannabis dependence symptoms, hospitalizations for cannabis exposure, increased emergency department (ED) visits for cannabis intoxication, and more adults seeking treatment voluntarily.17–20 Epidemiological research in Colorado, where cannabis was legalized in 2014, found no increase in cannabis use postlegalization for nonmedical use.21 However, in the first year postlegalization (2013–2014), there was an increase in ED visits for cannabis use, but it was followed by a second-year decrease.21,22 There was also an increase in accidental poisonings among children (measured through poison control calls) which has remained stable since legalization.21,23 The authors encouraged caution around the interpretation since legalization may have reduced the stigma of disclosure and resulted in a reporting increase without an underlying increase in incidence.

In a more recent comparison of Colorado to two states where cannabis remains illegal, cannabis use was found to have an overall neutral impact on healthcare utilization.24 The authors note that this could be accounted for somewhat by an overall reduction in hospital admissions and chronic pain admissions. This is consistent with evidence in some American states where cannabis legalization is associated with a reduction in opioid prescriptions and reductions in hospitalizations for opioid use disorder, opioid overdoses, and fewer prescription opioid medication deaths.25–28

A major limitation of the literature on the effect of legalization of medical and nonmedical cannabis on health service use is that studies focus primarily on a single jurisdiction in the United States of America (USA). As cannabis is still criminalized federally in the USA, comparisons to the impacts of Canadian legalization may not be an accurate comparison. There is therefore a need for further examination of Canadian trends and data. Alberta Health Services (AHS) is the publicly funded healthcare organization for the province of Alberta. The administrative data available provides the opportunity to investigate characteristics of individuals who report using cannabis in the past 12 months and who also received treatment for substance misuse. The current study serves as a prelegalization baseline in anticipation of postlegalization comparison.


Patient data from AHS were extracted from several administrative databases for the fiscal years 2012/13 to 2017/18. These data were linked and analyzed to examine trends in demographics and health care utilization over the 6-year period. Ethics approval was received from the University of Alberta Health Research Ethics Board (PRO00091078).

Client identification

Patients were identified for inclusion in the data set using the Addiction and Mental Health System for Information and Service Tracking (ASIST) database. ASIST is a clinical application used in substance misuse outpatient, residential, detoxification, and opioid dependency program services in the publicly funded health system in Alberta and includes information on demographics and substance use at the time of service enrolment. The population that receives substance use treatment from AHS may not be identical to those who receive privately funded treatment, however there is no data available for comparison at this time. Clients were identified based on their first enrolment (ie, index enrolment) in any AHS substance misuse service during a fiscal year and subsequent repeat enrolments within the same fiscal year were excluded.

Cohort creation

The index enrolment in each fiscal year was identified for all unique clients with a valid personal health number (PHN). Clients were excluded if they did not have a valid PHN. Exclusions due to missing PHNs varied each year but decreased from 37.7% in 2012/13 to 13.7% in 2017/18. During this period work was done in the system to increase the inclusion of PHN in the administrative databases. Clients may have been enrolled in more than one year, thus have appeared in more than one cohort. Three cohorts (Table 2) were created based upon two questions asked upon enrolment in substance misuse treatment services. These questions were: (1) Have you used the substance one or more times in the past 12 months? (2) Have you been concerned about this substance use in the past 12 months? For each question, clients respond either yes or no to a list of 17 substances.

Cohorts included in the analysis consisted of three comparison groups. These were: (1) Clients entering substance use treatment who used cannabis in the last 12 months compared to clients entering substance use treatment who did not use cannabis in the last 12 months, (2) Clients who used cannabis in the last 12 months who were not concerned with their cannabis use, compared to clients who used cannabis in the last 12 months who were concerned with their cannabis use, and (3) Clients who were only concerned with their cannabis in the last 12 months compared to clients who were only concerned about their alcohol use in the last 12 months and clients who were concerned about two or more individual substances (excluding cannabis and alcohol) in the last 12 months.

After creating the cohorts, demographic and temporal trends were investigated. Using personal health numbers (ie, PHNs), emergency department, acute care service use, and practitioner claims data were linked to examine service utilization and mental health comorbidities. The analysis was performed in SAS Enterprise Guide 7.1. Binary and categorical variables were presented as raw counts (n) and percentages and P-values were calculated using chi-square. Means and standard deviations are presented for continuous variables and P-values were calculated using ANOVA.


Mental health comorbidities were identified using the Discharge Abstract Database (DAD), the National Ambulatory Care Reporting System, and the Practitioner Claims Database. These databases capture admissions to acute care facilities, ED visits, and visits to practitioners funded by the public system (primarily physicians), respectively, and include diagnostic information (ICD-10 codes in DAD and National Ambulatory Care Reporting System; ICD-9 codes in practitioner claims). A client was considered to have a history of a comorbid condition if, within a 2-year retrospective window from their initial enrolment for substance use treatment, they had at least one hospital record, ED record, or three physician claims within a single fiscal year with an ICD9/10 code related to addiction and mental health. Healthcare utilization was examined using personal health records to identify any records of ED visits, hospital admissions, or records of substance misuse treatment such as the opioid dependency program, detox, or outpatient substance misuse services.


Missing data

After stratifying by age and sex, analysis showed that the excluded clients with missing PHN data on average were 3.1 years younger and 6.8% more likely to be male than those with valid PHNs. Missing data on the substances of concern question increased over time from 8.5% in 2012/13 to 23.9% in 2017/18. Clients with missing substance of concern data were more likely to be female and unemployed. Clients who reported cannabis use or concern about their use were less likely to have a valid PHN when compared to other substances, however, this difference was minimal (2.48%).

Unique client analysis

The total number of unique clients across the study period was 102,392 with 23,000 to 25,000 seeking treatment each fiscal year. Of the 102,392 unique individuals, 37.9% were enrolled two or more times during the 6-year period. The total number of enrolments per fiscal year (ie, clients may have enrolled in treatment more than once in a fiscal year), ranged from 31,000 to 34,000. The following analysis includes unique clients with a valid PHN (N = 88,502).

Past-year cannabis use

The overall number of clients indicating they have used cannabis in the past 12 months increased by 33.5%, from 6442 in 2012/13 to 8599 in 2017/18. The proportion of individuals reporting past-year cannabis increased by approximately 6% over the years (Table 1), with 54.5% of clients reporting past-year cannabis use in 2017/18. Increases in cannabis use were reported in both male and female clients. However, the proportion of males versus females was similar among cannabis users versus nonusers, and this pattern did not vary significantly over time (Table 1).

Table 1 - Demographic Profiles Among Enrolled Clients who Did (+) and Did Not (-) Report Using Cannabis in the Past 12 months, Alberta, 2012/13 to 2017/18
2012/13 2013/14 2014/15 2015/16 2016/17 2017/18

+ + + + + +
Total N 6442 6767 7002 6719 8018 6884 8146 7143 8362 7241 8599 7179
Cannabis use % 48.7 51.0 53.8 53.3 53.6 54.5
Age MeanSD95%CI 30.4112.0030.12, 30.70 41.6012.6941.30, 41.90 30.1911.6729.92, 30.46 41.2812.8640.97, 41.59 30.0111.3529.76, 30.26 41.0812.7640.78, 41.38 30.8211.2230.58, 31.06 40.9812.7140.69, 41.27 31.3211.0931.08, 31.56 41.3013.0241.00, 41.60 31.1111.3130.87, 31.35 41.0512.9940.75, 41.35
Female %95%CI 38.6738.65, 38.68 38.1138.10, 38.13 36.9636.95, 36.97 36.7336.72, 36.75 37.5037.49, 37.51 35.8135.79, 35.82 36.9036.89, 36.91 37.0437.03, 37.06 36.6736.65, 36.68 37.6637.65, 37.67 37.4737.46, 37.48 38.1438.13, 38.15
Male %95%CI 61.0461.02, 61.05 61.5061.49, 61.52 62.7862.77, 62.80 63.0363.02, 63.04 61.9761.96, 61.98 63.8063.79, 63.81 62.4762.46, 62.48 62.2362.22, 62.24 62.2662.25, 62.27 61.4861.47, 61.50 61.6061.59, 61.61 61.0161.00, 61.02
Includes only clients with a valid personal health number.

Age analysis showed that younger clients were more likely to report past-year cannabis use (Fig. 1). Across all reporting years, over 90% of clients under 18 years of age and over 70% of those aged 18 to 24 years enrolled in substance misuse services reported past-year cannabis use. In comparison, older clients were least likely to report past-year use, with an average of 19.1% of clients aged 55 years and older and 31.95% of those aged 45 to 54 reporting use within the last year. Over time, the largest increase was in the 55 and above age group with a reported 28.6% relative increase in use from 17.0% to 21.9%. The second-largest increase was seen in clients aged 35 to 44 whose reported use rose from 38.8% in 2012/13 to 48.2% in 2017/18, indicating a 24.2% relative increase. The only age group where reported use reduced was in those under 18 years, with a slight reduction from 93.4% to 91%, a 2.6% relative decrease.

Figure 1:
Proportion of unique clients who use cannabis by age group and fiscal year, Alberta 2012/13 to 2017/18.

Cannabis concern

Cannabis concern decreased over the 6 years preceding legalization, with the proportion of individuals expressing concern with their past-year cannabis use decreasing from 35.0% in 2012/13 to 25.3% in 2017/18 (Fig. 2). Both males and females expressed reduced concern, with a reduction from 35.4% to 26.1% in males and 34.3% to 24% in females during the study. Analysis of age categories revealed that while concern decreased in all ages, it reduced most significantly in individuals aged 55+ with a reduction from 33.2% in 2012/13 to 19.9% in 2017/18. Individuals under the age of 18 showed the least concern throughout the study, except for in 2017/18 where individuals aged 55+ reported the least cannabis concern. Individuals aged 45 to 54 reported the highest levels of concern throughout the time period.

Figure 2:
Proportion of unique clients who reported past-year cannabis use and concern about their cannabis use by age group, Alberta 2012/13 to 2017/18.

Cohort comparison

Healthcare utilization, diagnostic comorbidities, and demographics were examined for the three cohorts, these were: (1) clients reporting past-year cannabis use compared to clients reporting no past-year cannabis-use, (2) clients reporting concern over their past-year cannabis use compared to clients who used cannabis but did not report concern, and (3) clients only concerned about their cannabis use compared to alcohol concern only compared to polysubstance use (excluding cannabis and alcohol).


When comparing clients who reported past-year cannabis use and those who did not, those with past-year use were approximately 10 years younger, less likely to have achieved a high school degree, and more likely to be unemployed. Those concerned about their cannabis use were also less likely to be employed than those not concerned. Clients only concerned about cannabis use were on average 10 years younger than clients concerned about multiple substances, 15 years younger than clients concerned about only alcohol use, and less likely to have completed high school than those concerned about only alcohol use or polysubstance use (P < 0.001).

Diagnostic comorbidities

When examining comorbidities, those who reported using cannabis were more likely to have a developmental, personality, or mood disorder diagnosis in the past 2 years than clients who did not report past-year cannabis use (Table 2). All ICD-10 codes for addiction and mental health diagnoses were examined and clinical experts were consulted on diagnoses groupings to report on (see supplementary table, There were no significant differences in other mental health disorders examined. Clients reporting concern about their cannabis use were more likely to have mood, anxiety, developmental, and personality disorder diagnosis in the past 2 years compared to others who used cannabis, but were not concerned about their use. When comparing cannabis, alcohol, and polysubstance use concern, clients who were concerned solely about cannabis use were less likely to have a substance use disorder diagnosis (P < 0.001).

Table 2 - Mental Health Comorbidities Among Enrolled Clients who Did (+) and Did Not (-) Report Using Cannabis in the Last 12 months, Alberta, 2012 to 2018
2012/13 2013/14 2014/15 2015/16 2016/17 2017/18

+ + + + + +
Total n 6442 6767 7002 6719 8018 6884 8146 7143 8362 7241 8599 7179
Mood %95% CI 58.1858.17, 58.20 56.8656.85, 56.88 59.3759.36,59.38 57.5757.55,57.58 59.0559.04,59.07 57.5157.50,57.52 58.2458.23,58.25 56.1156.10,56.12 57.9057.89, 57.92 55.6155.60,55.63 54.9754.96,54.98 52.6552.64,52.67
Anxiety %95% CI 50.3150.30, 50.33 50.5450.52, 50.55 51.9151.90,51.93 51.4551.44,51.47 52.6652.64,52.67 52.3052.28,52.31 53.2553.24,53.27 52.5152.50,52.53 52.5652.55, 52.57 50.7050.68,50.71 51.4451.42,51.45 49.8459.83,49.85
Developmental %95% CI 21.0321.02, 21.05 10.8310.82, 10.84 22.0822.07, 22.09 11.7611.75,11.77 22.5422.53,22.55 11.9011.89, 11.91 21.0221.01, 21.03 11.9711.96, 11.98 21.0121.00,21.02 11.6311.62, 11.64 21.8721.87, 21.88 11.0511.04, 11.06
Personality %95% CI 19.8419.83, 19.85 14.7514.74, 14.76 19.0919.08, 9.11 15.0315.02, 15.04 18.4518.44, 18.46 14.5414.53,14.55 17.2717.26, 17.28 14.1314.12, 14.14 17.6517.64, 17.66 13.4513.44, 13.46 16.2616.25, 16.27 12.7512.74, 12.76

Healthcare utilization

There were no differences in healthcare utilization between those reporting past-year cannabis use and those who did not report cannabis use. However, in comparison to those with no cannabis use concern, clients who reported concern with their past-year cannabis use were less likely to enroll in opioid dependency programs, more likely to enroll in detoxification programs, and more likely to attend the ED or be admitted to hospital (Table 3). In comparisons of cannabis, alcohol, and polysubstance use concern cohorts, patterns of service utilization varied across the three cohorts, with clients concerned about alcohol use only or polysubstance use using most healthcare services more frequently, particularly ED (P < 0.001).

Table 3 - Past-Year Healthcare Utilization Among Clients who Did (+) and Did Not (-) Report a Concern About their Cannabis Use in the Previous 12 Months, Alberta, 2012 to 2018
2012/13 2013/14 2014/15 2015/16 2016/17 2017/18

+ + + + + +
Total n 2235 4151 2362 4560 2556 5362 2508 5525 2288 5961 2144 6338
Cannabis concern % 35.00 34.12 32.28 31.22 27.74 25.28
Detox %95% CI 22.1522.11, 22.19 17.6617.64,17.68 20.2820.25,20.31 17.6317.61,17.65 24.1024.07,24.13 18.8218.81,18.83 23.7223.69,23.75 21.8721.86,21.88 21.0220.99,21.05 19.7119.70,19.72 22.1122.07,22.15 21.3321.32,21.34
Opioid dependency program %95% CI 0.450.44, 0.46 1.731.72, 1.74 0.550.54, 0.56 1.751.74, 1.76 0.590.58, 0.60 2.202.19, 2.21 0.760.75, 0.77 2.282.27, 2.29 1.701.69, 1.71 3.443.43, 3.45 2.122.11, 2.13 5.955.94, 5.96
Emergency department Visits mean SD95% CI 3.57 6.623.30, 3.84 3.09 5.962.91, 3.27 3.70 6.653.43, 3.97 3.16 6.282.98, 3.34 3.59 6.023.36, 3.82 3.26 6.033.10, 3.42 3.55 5.913.32, 3.78 3.21 5.323.07, 3.35 3.91 6.473.64, 4.18 3.56 7.003.38, 3.74 4.29 9.153.90, 4.68 3.65 6.243.50, 3.80
Hospital admissions mean SD95% CI 1.19 2.981.07, 1.31 0.78 2.270.71, 0.85 1.16 2.961.04, 1.28 0.84 2.340.77, 0.91 1.16 2.881.05, 1.27 0.80 2.330.74, 0.86 1.06 2.860.95, 1.17 0.81 2.320.75, 0.87 1.31 3.081.18, 1.44 0.83 2.360.77, 0.89 1.28 2.921.16, 1.40 0.89 2.410.83, 0.95


The data presented in the current study provides an overview of the characteristics of individuals seeking treatment for substance misuse in Alberta before nonmedical cannabis legalization in 2018. During the 6 years before legalization, the number of individuals reporting cannabis use among Albertans accessing substance misuse services increased by 33.5%, and over half of clients accessing addiction services in the year before legalization reported using cannabis in the prior year. This increase mirrors trends seen throughout Canada that may be associated with decreases in risk perception since medical legalization and discussions around legalization for nonmedical purposes.4–6 While the number of individuals reporting cannabis use, in general, has increased, the percentage of individuals entering addiction treatment who report past-year cannabis use has not changed, indicating similar rises in the number of individuals accessing services for substances other than cannabis. It is important to note that these increases may be partially due to changes in data availability, with a 24.6% (absolute) increase in linkable data during the study period.

Of those individuals receiving treatment for substance misuse, some of the largest reported changes were seen in individuals over 55. In this age group, the prevalence of reported past-year cannabis use increased, while concern about cannabis use decreased significantly. It may be the case that decreased concern led to increased cannabis use. Future research in these populations, including qualitative work, may be valuable to further assess and clarify these observations. In particular, the relationship between opioid use, healthcare utilization, and the normalization of cannabis use in those over 55 requires further research.

Younger populations, notably those under 18 years, reported the highest proportion of cannabis use throughout the study, with over 90% of individuals entering substance misuse services reporting cannabis use in the past 12 months. Furthermore, this age group also reported the least concerns about past-year cannabis use through most of the years studied. These figures should be interpreted with caution due to changes in PHN data availability, which was more pronounced in younger clients who are more likely to report cannabis use. However, as heavy regular cannabis use in adolescence is thought to be a risk factor for later psychotic illness these results may indicate a need for early intervention in these age groups.8,12,13 Notably, results from this study show no significant differences in schizophrenic mental health comorbidities between those using cannabis and those using other substances. Individuals who reported using cannabis were however more likely to have developmental, personality or mood disorders.

Healthcare utilization varied throughout the study, with no differences in healthcare utilization seen in individuals who reported past-year use of cannabis in comparison to those who did not. However, clients who expressed concern about cannabis use had more ED visits and were more often admitted to inpatient care than those with no cannabis use concern. Individuals who reported cannabis concern were also less likely to enroll in opioid dependency programs and more likely to enroll in detoxification services. This may be due to cannabis being the main drug of choice in individuals expressing concern, or alternatively individuals who use opioids may perceive cannabis as less concerning, thus future analysis should also examine rates of concurrent drug use. When comparing alcohol and polysubstance use concern, those concerned about their cannabis use had fewer substance misuse treatment enrolments, ED visits, and hospital admissions than both polysubstance use and alcohol use clients. At this time, it cannot be determined whether these attendances were related to substance use or other health concerns, therefore these could include health issues not directly related to substance misuse. Future data analysis should aim to ascertain the proportion of healthcare utilization which can be directly attributed to substance use. The observed differences may also have been related to other factors, such as differences in the age distribution of users versus nonusers. Future analyses is planned to examine this population in the period postlegalization, and will incorporate multivariable methods to examine these associations in more detail. These findings should be interpreted with caution, as the earlier years had a higher percentage of missing data and the increase in the number of PHNs available for analysis may have impacted rates of reported cannabis use and concern. This may be particularly notable when taking into consideration that the increase was primarily younger individuals, who reported higher rates of cannabis use. It is unclear what led to the increase in linkable data, perhaps increased training and focus on collecting personal health numbers system wide, as the increase was throughout the substance misuse treatment continuum and not driven by a single type of service. It is important to note that only a small fraction of addiction and mental health clients with AHS identify their only concern as cannabis. Furthermore, expressing concern about cannabis use does not mean that cannabis is the client's only substance of choice.

To our knowledge, this is the first detailed descriptive analyses of cannabis users among individuals seeking addiction treatment in Canada, with comparative data on health care utilization and comorbidities. The information presented in this study provides a baseline examination of the characteristics of clients entering substance use treatment within Alberta who report past-year cannabis use. These data will be used in the future to provide a pre- and postlegalization comparison of cannabis use and concern in Albertans. In particular, the findings surrounding health care utilization should be monitored to assess health system level impacts and subsequently inform health policies within AHS and the wider Canadian health system.


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cannabis; concern; demographics; healthcare utilization; pre-legalization; cannabis; préoccupation; démographie; utilisation des soins de santé; pré-légalisation

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