Substance Use by Canadian Youth - A National Survey of Canadians' Use of Alcohol and Other Drugs - Canadian Addiction Survey (CAS)

Chapter 4: Cannabis Use and Harms

Highlights

• 61.4% of youth have used cannabis in their lifetime, and 37.0% have used it at least once in the past 12 months
• The mean age at which youth reported having the first chance to try marijuana, had they wanted to, was 14.6 years. The mean reported age of first use was 15.6 years.
• Lifetime use was higher in youth aged 18 to 19 (69.9%) and 20 to 24 (68.5%) than those aged 15 to 17 (39.3%). In addition, the rate of past-year use was highest in youth aged 18 to 19 (47.2%) followed by those aged 20 to 24 (36.5%) and 15 to 17 (29.2%).
• Males were more likely than females to have used cannabis in their lifetime (64.7% versus 58.0%) and in the past year (41.4% versus 32.3%).
•  Almost 1 in 10 (8.2%) Canadian youth uses marijuana on a daily basis. Among current users, more than 1 in 5 (22.3%) youth reported using it on a daily basis over the past 3 months.

Introduction

The focus of this chapter is on the use of cannabis, such as marijuana or hashish, in youth. The lifetime and past-year prevalence of cannabis use and various concerns related to its use will be explored.

Lifetime prevalence is based on the question asking respondents whether they have "ever used or tried marijuana, cannabis or hashish" and past-year prevalence is based on a follow-up question about whether they also used the drug at least once in the past 12 months.

To examine age at which respondents first had the chance to try marijuana, all respondents were asked the question, "About how old were you when you first had a chance to try marijuana or hash if you had wanted to?" Respondents who reported having used marijuana in their lifetime were asked a follow-up question, "How old were you when you started using marijuana, cannabis or hashish?"

To examine the frequency with which current users consume marijuana or hashish, past 12-month users were asked, "How often did you use marijuana, cannabis or hashish in the past 3 months?" and given the opportunity to respond never, less than monthly, monthly, weekly, daily or almost daily.

To assess cannabis problems, five items of the ASSIST screener developed by the World Health Organization (WHO) were used (WHO ASSIST Working Group, 2002). Only respondents who reported having used cannabis during the 3 months prior to the survey were asked questions on the ASSIST. The questions were: (1) how often they had a strong desire or urge to use cannabis, (2) how often their use of cannabis led to health, social, legal or financial problems, (3) if they failed to do what was normally expected of them because of their use of cannabis, (4) whether a friend or relative or anyone else ever expressed concern about their use of cannabis, and (5) whether they ever tried and failed to control, cut down, or stop using cannabis. Items 1 through 3 refer to problems they might have experienced in the past 3-month period and items 4 and 5 refer to problems in their lifetime.

Results

Youth were more likely to have used cannabis in their lifetime (61.4% versus 41.8%) and to currently use it (37.0% versus 10.0%) than adults (Table 4.1).

Older youth, those aged 18 to 19, were more likely than those aged 15 to 17 to have reported lifetime use of cannabis (69.9% versus 39.3%). There was no difference in reported lifetime use between those aged 18 to 19 and those 20 to 24 years of age (69.9% versus 68.5%) (Table 4.1). After age 24, however, the reported lifetime use of cannabis is significantly lower and continues a steady decline across age groups until reaching a reported rate of 3.1% among those aged 75 or older (Figure 4.1).

Figure 4.1: Percentage of Canadians who used cannabis in lifetime, Canada 2004

A similar trend is apparent for past-year reported cannabis use. Youth aged 18 to 19 were significantly more likely than those aged 15 to 17 to report using cannabis in the past 12 months (47.2% versus 29.2%). A steady decline is apparent after the age of 19, with those 20 to 24 significantly less likely than those 18 to 19 to report past-year use of cannabis (36.5% versus 47.2%), and this significant decline continues across other age categories until it drops to 1.1% among those 65 to 74 years of age (Table 4.1, Figure 4.2).

Figure 4.2: Percentage of Canadians who used cannabis in the year preceding the survey, Canada, 2004

Although these rates and charts take into account lifetime use considering use at least once ever, and past-year use considering use at least once in the past 12 months, when excluding one-time use, the pattern of use remained similar with 54.5% of youth reporting having used marijuana more than once in their lifetime, and 36.0% having used more than once in the past 12 months. These rates in youth were significantly higher than those reported by adults; only 34.9% of adults reported having used more than once in their lifetime and 9.8% having done so more than once in the past 12 months (Table 4.1).

Typically, among adults as well as the general population aged 15 or over, males were more likely than females to report lifetime, current and past 3-month use of marijuana (Table 4.1). Among youth overall, this pattern was also evident with the exception of lifetime use in which there was no difference between males and females. When broken down even further among the age categories of 15 to 17, 18 to 19 and 20 to 24, the only significant difference between males and females was among 18- to 19-year-olds in which males were more likely than females to have reported lifetime use of cannabis (77.9% versus 60.7%), and among the 20- to 24-year-old group where males were more likely than females to have reported current use (41.7% versus 29.3%) and past 3-month use (35.0% versus 24.0%). Among youth aged 15 to 17, around the age of first use, there was no difference between males and females in reported cannabis use (Table 4.1).

These results are consistent with many other findings on youth initiation into substance use. The prevalence rate for males and females is usually the same around the age of first use (in this case 15 to 17 years old). However, as we examine older cohorts, males tend to have higher rates of use than females. This is also the case for alcohol use, as examined in the previous chapter in which, among youth, there was no difference between males and females aged 15 to 24, 15 to 17, 18 to 19, or 20 to 24 in their reported rate of lifetime and past-year alcohol use; however, adults males aged 25 or over were more likely than the females to have used alcohol in their lifetime and in the past 12 months.

Predictors of Lifetime and Past 12-Month Cannabis Use

To examine the characteristics of youth who reported lifetime or past-year cannabis use, two multivariate logistic regressions were conducted, taking into account sex, age, region, household location and income adequacy as predictors (Tables 4.2 and 4.3).

In terms of the characteristics of youth who reported lifetime use of cannabis, there were main effects of age and region (Table 4.2). Youth aged 18 to 19 were more likely than those aged 15 to 17 to have reported lifetime use of cannabis (69.9% versus 39.3%): there was no difference between reported lifetime use of those aged 18 to 19 and those 20 to 24. In addition, youth from the Atlantic region were less likely (51.4% versus 61.4%) and those from the Quebec region were more likely (73.1% versus 61.4%) than youth from the rest of Canada to have reported lifetime cannabis use.

In terms of the characteristics of youth who reported past-year use of cannabis, there were significant differences in terms of sex, age, region and household location (Table 4.3). Males were more likely than females (41.4% versus 32.3%), those aged 18 to 19 were more likely than those aged 15 to 17 (47.2% versus 29.2%) and 20 to 24 (47.2% versus 36.5%), youth from Quebec were more likely than those from the rest of Canada (46.1% versus 37.0%), and those from non-rural locations were more likely than those from rural locations (38.5% versus 26.5%) to have reported past-year cannabis use.

Age of Chance to Try/Age of First Use

As with alcohol, age of cannabis initiation has also been associated with psychosocial adjustment and conduct problems in youth (Fergusson and Horwood, 1997; Pedersen, Mastekaasa and Wichstrom, 2001) as well as the subsequent use of other drugs (Fergusson and Horwood, 2000; Lynskey, et al., 2003). As such, the age of initiation of cannabis use among youth was examined and then controlled for as a predictor in the following regressions.

The mean age at which youth reported to have had the chance to try marijuana, had they wanted to, was 14.6 years; there were no differences between males and females. Among youth who had used cannabis at least once in their lifetime, the mean age at which they reported having started using was 15.6 years; again there were no differences between males and females in the reported age of first use (Table 4.4). It is noteworthy that there was a year time span between the age at which youth first had the chance to try cannabis, and actually did. One area for future exploration would be to examine the factors responsible for this gap in order to develop initiatives to prevent youth from using at all, or to prolong this delay in initiation even further.

The mean age at which youth first had the chance to try, or actually first used, cannabis was higher than that demonstrated among the total population and among adults. Among the total population, the mean age at which respondents first had the chance to try cannabis and actually first used cannabis was approximately 19 years. Among adults aged 25 to 44, the mean age at which they had the first chance to try was approximately 17 years, and 18 years for first use, whereas among those 45 or older it was approximately 24 and 23, respectively. It is important to note that the mean age at which respondents first had the chance to try includes the total population, whereas the mean age of first use takes into account only those respondents who had used (hence for those aged 45 or older, the mean age at first use was lower than the mean age to try).

These results must be interpreted with caution since from the data available it is not possible to determine whether the younger reported age of first use that is displayed by youth indicates a decrease in the age of initiation over time, or if it is the result of an age-specific recall effect or cohort effect. An age-specific recall effect refers to the tendency to shift estimates of age of onset upwards as individuals become older. More specifically, as time passes between the actual time when one first had the chance to try and the time when one is probed for this information, they may have difficulty recalling precisely the actual number, resulting in their answer being slightly off. As a result, due to this recall effect, the mean age at which adults stated they first used cannabis may be slightly different from that found for youth due to their lack of precision recalling this age. An alternative explanation for the differential mean age of first use could also be a cohort effect; adults have had more years to have actually used cannabis and this in turn results in their mean age of actual use being higher than that found among youth. Since youth is defined as those between the ages of 15 and 24, the oldest possible age for having used is 24; this confined range influences the mean age of first use among youth, causing it to be smaller than that of adults. In adults, the oldest possible age is much higher, so if there are some adults who began using at older ages, this would result in the mean for adults being higher.

These two possible explanations are important to keep in mind when examining the differences in the mean age of use between youth and adults. While the differences in the mean age of use between youth and adults may reflect the fact that youth are currently using at an earlier age, one cannot rule out these two other possible explanations. Examining the median instead of the mean affords the advantage that extreme cases (such as someone whose age of initiation was 75) do not influence the estimate; however, it does not rule out these other confounding explanations.

In terms of region, youth from the Atlantic region had a significantly older mean age of cannabis initiation (16.1 years) than youth from the rest of Canada (15.6 years), whereas those from the Quebec region had a significantly younger mean age of cannabis initiation (15.2 years).

Frequency of Cannabis Use Among Youth

To examine the frequency with which respondents consume marijuana, respondents who had used cannabis in the past year were asked, "How often did you use marijuana, cannabis or hashish in the past 3 months"? Respondents were given the opportunity to respond never, less than monthly, monthly, weekly or daily/almost daily in order to examine the frequency of use among current users.

As with Canadians 15 years of age or older, the frequency of past 3-month reported marijuana use, among current users aged 15 to 24, was evenly distributed across the five categories of never, once or twice, once a month, once a week, and daily (Figure 4.3; Table 4.5). Overall, about one fifth of youth current users did not use marijuana in the past 3 months (19.5%), almost one quarter used it one or twice (23.5%), 13.3% used once a month, more than one fifth used once a week (21.4%), and more than one fifth (22.3%) used on a daily basis. In terms of the frequency of past 3-month use among current users, there were no differences between youth and adults in terms of their frequency of use, with the exception of "daily use"; a higher proportion of youth reported consuming cannabis on a daily basis (22.3% versus 15.0%).

Figure 4.3: Frequency of past 3-month cannabis use among current users

Among youth, there are no differences apparent between frequency of cannabis use for males and females. However, among adult users of cannabis a higher proportion of females tended to report never using whereas a higher proportion of males reported weekly or daily use (Table 4.5).

In terms of the past 3-month frequency of cannabis use among the total sample of youth overall, approximately 70.3% reported never using cannabis, 8.7% reported doing so at least once or twice over the past 3 months, 4.9% reported doing so monthly, 7.9% reported doing so weekly and 8.2% of youth reported daily cannabis use (Table 4.6). Youth were more likely than adults to have reported using once or twice, monthly, weekly or daily, but less likely to have reported never. No differences were observed in the frequency of cannabis use between youth aged 15 to 19 and those aged 20 to 24. While only 2.5% of the total population aged 15 years of age or over have reported consuming cannabis on a daily basis (Table 4.6), it is important to highlight the fact that youth account for over half of these individuals. More specifically, 52.4% of Canadians who used marijuana on a daily basis were youth.

Among the total sample of youth, females were more likely than males to report having never used cannabis (75.4% versus 65.3%), whereas males were more likely than females to have reported weekly (10.2% versus 5.5%) or daily (10.8% versus 5.5%) use (Table 4.6).

Characteristics of Youth Who Use Cannabis on a Weekly/Daily Basis

In terms of the characteristics of youth who use on a weekly or daily basis compared with those who did not, among current users, there were main effects of sex, age, income and age of cannabis initiation (Table 4.7). Males who had used in the past 12 months were more likely than females to have reported daily or weekly use of cannabis (50.9% versus 34.1%, respectively), the odds of youth aged 18 to 19 reporting weekly or daily use were 4 times higher than for those aged 15 to 17 (36.3% versus 53.7%), those who did not state their income status were more likely than those in the lowest income adequacy group (52.9% versus 28.3%), and those who started using cannabis at a younger age were more likely to report weekly or daily cannabis use than those who started using later.

Cannabis Problems

Table 4.8 shows the five problem indicators of the ASSIST scale. Among youth a large proportion of past 3-month users experienced problems from their use; almost half (45.9%) experienced "a strong desire to use cannabis in the past three months" and "failed control over their use" (54.0%), almost one tenth (8.9%) experienced "health, social or legal problems", over one tenth (12.2%) experienced "failed expectations", and almost one third (27.3%) experienced "friends concern over their use".

Adults were less likely than youth to have reported having experienced a "strong desire to use" (36.2% versus 45.9%), "health, social, legal problems" (4.1% versus 8.9%), "failed expectations" (6.2% versus 12.2%), "friends concern over use" (14.1% versus 27.3%), or "failed control" (34.5% versus 54.0%). Other than "failed control", there were no differences between youth aged 15 to 19 and those aged 20 to 24 in terms of reported harms; youth aged 15 to 19 were more likely than those aged 20 to 24 to report having had "failed control" over their cannabis use (61.7% versus 47.1%).

Among past 3-month users aged 15 to 24, there were no differences between males and females in the proportion who reported harm in each of the five areas. This finding is different from that among adults in which females were more likely than males to report "failed expectations" (11.8% versus 4.1%) but less likely to report "friends concern" (8.7% versus 16.2%) or "failed control" (24.8% versus 38.2%).

To examine the characteristics of past 3-month users aged 15 to 24 who had experienced at least one problem due to their cannabis use compared with those who had not, a multivariate logistic regression was conducted taking into account sex, age, region, household location, income status and age of cannabis initiation (Table 4.9). The younger that youth started using cannabis, the more likely they were to have reported experiencing at least one problem due to their cannabis use. When taking cannabis frequency into account, however, age of cannabis initiation was no longer significant, but instead the frequency with which past 3-month cannabis users used cannabis was predictive of whether or not they reported harms. The odds of those who used daily or weekly reporting harms were over 4 times higher that of those who used less than monthly (95.1% and 87.4% versus 61.4%).

Patterns/Reasons of Use

The most common place for youth to consume marijuana was at home (42.1%), followed by parties (37.8%), and parks, street, outdoors (12.1%). A higher proportion of adults responded that the most common place to consume marijuana was at home (69.0%), followed by a smaller proportion, than that of youth, who stated at parties (22.1%). The most frequent place of consumption was different for youth aged 15 to 19 and those aged 20 to 24. Only 23.4% of youth aged 15 to 19 usually consume marijuana at home, with the most frequent place of consumption being parties (46.7%). The most common place for 20- to 24-year-olds to consume marijuana was at home (59.4%), followed by parties (29.6%).

Youth reported that they usually consume marijuana with friends (86.0%) or friends and family (8.9%). This pattern is slightly different from that of adults, in which a much lower proportion of adults usually consume marijuana with friends (60.6%), and a higher proportion than that found in youth reported consuming marijuana alone (16.9%). In addition, 9.5% of adults responded with family, compared with 1.6% of youth.

The majority of youth stated that their main reason for using the first time was "to try out or due to curiosity" (57.0%); this is similar to that found for adults (51.7%).

When asked how respondents get their marijuana, in reference to the last time they used, the majority of youth responded that they "got it for free" (57.4%) as did adults (55.6%). The next most common method of obtaining marijuana was buying it (40.4% and 39.6%, respectively).

Summary and Discussion

Although the prevalence of cannabis use was lower than that of alcohol, a large proportion of Canadian youth used cannabis or had at some point in their lives. The prevalence of cannabis use in youth was higher than that of adults for both lifetime (61.4% versus 41.8%) and past 12-month use (37.0% versus 10.0%). As with alcohol, when it comes to cannabis use, youth are not a homogeneous group. There were no differences between males and females in terms of lifetime use; however, males were more likely than females to report current use. In addition, 15- to 17-year-olds were less likely to report either lifetime or current cannabis use than youth aged 18 to 24. In terms of frequency, males were more likely to use cannabis more often than females, as were youth aged 18 to 24 compared with 15-to 17-year-olds.

Regarding the overall prevalence rates, youth from Quebec had a higher prevalence of lifetime and current cannabis use than the national average, whereas those from the Atlantic region had a significantly lower prevalence of lifetime use. This is interesting given that youth from Quebec also had a higher prevalence of alcohol use and a younger age of alcohol initiation. Youth from the Atlantic region had a later age of alcohol initiation, and yet here we see that they have a lower prevalence of cannabis use. This finding suggests that alcohol use and age of initiation may be factors associated with cannabis use. This will be examined in Chapter 6 when the combination use of substances, and how use of one substance impacts use of another, is explored.

The mean age at which youth first had the chance to try cannabis/hashish, had they wanted to try, was 14.6 years. However, the mean age at which youth actually tried was 15.6 years, the same age as the mean age of alcohol initiation. Exploration of the factors involved with this year delay in the actual use of cannabis may be of interest to those involved in policy or prevention. As with alcohol, youth from the Atlantic region also tried cannabis at an older age than those from the rest of Canada, whereas those from the Quebec region started using at a younger age than the national mean.

The mean age at which youth started using cannabis was associated with a higher frequency of cannabis consumption; youth who started using cannabis earlier were more likely to report using weekly/daily than those who started using cannabis at a later age. Related to this, although the main effect of region was not significant, Quebec youth were more likely to use cannabis weekly/ daily. This is not surprising given the relation between age of initiation and later patterns of use. When age of cannabis initiation was controlled for, however, this difference was no longer significant.

When asked what their single most important reason was for using cannabis their first time, the most common reason provided by youth, over half, was "curiosity/to try out". Although a large proportion of youth do not use cannabis or use it infrequently, it must be pointed out that 8.2% of youth overall use cannabis on a daily basis and 22.3% of current users report doing so. In addition, of the total population aged 15 or older, 2.5% use cannabis on a daily basis, and youth comprise over half of these individuals.