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Cannabis use among Australian adolescents: findings of the 1998 National Drug Strategy Household Survey

Cannabis use among Australian adolescents: findings of the 1998 National Drug Strategy Household... context and recent trends in cannabis use among Australian adolescents. Amanda Reid, Michael Lynskey and Jan Copeland National Drug and Alcohol Research Centre, University of New South Wales Method: Data was collected from 1,581 adolescents aged 14-19 years as part of the 1998 National Drug Strategy Household Survey, and comparisons were made with data from 350 adolescents who participated in the 1995 survey. Results: Among 14-19 year olds, 47.8% have had the opportunity to use cannabis in the past year and 45.2% have used cannabis at least once in their lifetime. Substantial increases have occurred since 1995 in the prevalence of use among young females. While most cannabis use was fairly infrequent, a minority of 14-19 year olds (9.4%) used cannabis at least weekly. Cannabis use was associated with regular tobacco and alcohol use, and other illicit drug use. Regular cannabis users had lower levels of health on the general health and vitality dimensions of the SF-36. Implications: These results show that cannabis availability and use is common among Australian adolescents, and confirm that there has been an increase in use between 1995 and 1998, although only among young females. Future research is required to understand why this recent increase has occurred, and trends in cannabis uptake and use patterns among this group should be carefully monitored. Interventions may need to be developed and made available to the group of young people who are using cannabis heavily. (Aust N Z J Public Health 2000; 24: 596-602) annabis is the most commonly used illicit drug in Australia and internationally. 1-2 Prevalence of use among Australian adolescents has increased over the past decade,3 with 36% of Australian secondary school students aged 12-17 years reporting cannabis use in 1996. 4 Recent media reports of cannabis-related school expulsions have highlighted community concern about the high rate of cannabis use by adolescents and the possible physical and psycho-social consequences of use. Research suggests that cannabis use may be associated with a variety of negative effects, such as impaired educational performance, initiation into other illicit drug use and adverse mental health.3 The patterns of heaviest cannabis use are likely to occur during late adolescence and early adulthood, increasing the risk of harmful acute effects and the potential for abuse and dependence.5 Adolescents have been found to be at greater risk of cannabis dependence than adults for a given dose.6 Earlier onset of substance use could also increase the risk of developing later substance-related problems.7-9 Previous studies on the prevalence of adolescent cannabis use have found marked age and gender differences. The prevalence of cannabis use has consistently been found to increase with age during adolescence1,3 and higher rates of cannabis use have been found among males across all age-groups. 3,10 Heavy use patterns are also more common among males.11-12 Although successive studies estimating the prevalence of lifetime use have documented an increase in use, the most recent estimates available are based on data collected during the 1996 Australian School Students’ Alcohol and Drugs Survey.4 This is the only national survey of school students that has been conducted, and there are problems in comparing the results of this national survey with those of previous regionally based school surveys. School surveys are also limited by the difficulties in generalising results to the wider adolescent population, as research has shown that adolescents who are out of school are more likely to engage in drug use.13 Therefore, the increase in cannabis use among the adolescent population is difficult to confirm and quantify, despite the importance of monitoring this trend. Additionally, the nature of the progression of this trend in the past few years is unknown. More recent data on the prevalence of adolescent cannabis use was collected during the 1998 National Drug Strategy Household Survey (NDSHS).14 This survey was the sixth in a series of household surveys on tobacco, alcohol and illicit drug use that have been conducted since 1985. Trends in the prevalence of adolescent cannabis use over the past few years can be more precisely determined using data from this survey series. A further benefit of the 1998 NDSHS is that it provides comprehensive data on the context of cannabis use and includes the SF-36 health questionnaire.17 This paper presents an analysis of the 1998 NDSHS data, and aims to estimate the prevalence of lifetime and recent cannabis use among Australian adolescents (aged 14-19 years) and to describe the frequency and context of cannabis use in this population. A further aim is to examine recent trends in the prevalence of cannabis use by comparing the Submitted: February 2000 Revision requested: August 2000 Accepted: November 2000 Correspondence to: Amanda Reid, National Drug and Alcohol Research Centre, University of New South Wales, Sydney, New South Wales 2052. Fax: (02) 9399-7143; e-mail: A.Reid@unsw.edu.au AUSTRALIAN AND NEW ZEALAND JOURNAL OF PUBLIC HEALTH 2000 VOL. 24 NO. 6 Cannabis use among Australian adolescents 1998 data with data from the 1995 survey wave.15 This paper also reports the associations between cannabis use, other illicit drug use and regular tobacco/alcohol use, and the associations between cannabis use and scores on the SF-36 health questionnaire. Method The 1998 National Drug Strategy Household Survey The 1998 survey was conducted by Roy Morgan Research and managed by the Australian Institute of Health and Welfare. Data were collected in the period July to mid-September 1998. A sample of 1,581 adolescents (823 females and 758 males) aged 14-19 years took part, constituting 15.8% of the total survey sample (n=10,340). The sampling procedure was designed to provide a near random sample of households within each specified geographic region across Australia. Three sampling methods were used. Sample 1 interviews were conducted in the respondent’s home, using a mixture of face-to-face interview combined with a confidential, sealed, self-completion questionnaire for sensitive sections (such as personal drug use behaviour). Eligible households were those containing at least one person aged 14 or over, and selection of the respondent was based on whose birthday next occurred. Sample 2 questionnaires were completed in the same households as Sample 1, by the youngest person aged 14 and over who had not been interviewed in Sample 1. Sample 2 completed an entirely self-administered questionnaire. Sample 3 questionnaires were completed by those aged 14-39 years in capital cities only, and again were entirely selfadministered. The data presented here are based on the combined three samples, since few significant differences were found between the samples in respect to drug use.16 Biased sampling towards the young and those living in capital cities contributed to specific differences between the combined sample and the known demographics of the Australian population. These differences were addressed by using weighted data to derive population estimates. In the final weighted combined sample, all regions and age/gender groups were represented in their correct proportions. The estimated overall response rate (for all three samples combined) was 56%, and was similar to previous waves of this survey. More detailed information regarding sampling methodology and design, response rates, derivation of weights and design effects can be found in the NDSHS: Technical Report 1998.16 The questionnaire included questions on a range of topics including drug-related knowledge, attitudes, use and behaviours relevant to alcohol, tobacco and a range of illicit drugs. However, only the data relevant to cannabis and correlates of its use are reported in this paper, and the specific questions relating to these areas are described below. Cannabis – Extent of cannabis use and associated behaviours were measured by a series of questions that were filtered 2000 VOL. 24 NO. 6 according to response. Respondents were asked if they had been offered or had the opportunity to use marijuana in the past 12 months, and in a separate section, if they had ever tried marijuana. If they had tried cannabis, they were questioned about age and circumstances of first use, asked if they had used marijuana in the past 12 months, and questioned about frequency of current use. If respondents had used cannabis in the past 12 months, they were asked additional questions on patterns of use. Tobacco, alcohol and other illicit drug use – Respondents were asked screening questions about their tobacco and alcohol use. If respondents had smoked a full cigarette in their lifetime, they were asked if they had smoked at least 100 cigarettes or the equivalent amount of tobacco in their life, and if they were currently smoking daily. Similarly, if respondents had consumed a full glass of alcohol in their lifetime, they were asked how often they had an alcoholic drink of any kind. Along with this measure of frequency, incidences of recent binge-drinking were obtained. A measure of any other illicit substance use was obtained by combining data collected individually for a number of illicit drugs. All respondents were also questioned about their favourite or preferred substances. Health status – The SF-36 (Short-Form 36) is a self-report questionnaire containing 36 items which measure health-related quality of life.17 The Australian version of this questionnaire (see Sanson-Fisher and Perkins (1998) for a description of psychometric performance) was included in the 1998 survey.18 The 1995 National Drug Strategy Household Survey The 1995 survey was conducted by AGB McNair. Data were collected over the months of May and June 1995. A sample of 350 adolescents (201 males, 149 females) aged between 14 and 19 years (9% of the total sample) completed the interviews. A single sample design was used. All respondents completed a confidential sealed section, along with a separate, intervieweradministered questionnaire. The total sample response rate was 57% of the households actually contacted. Person-specific weights were also calculated for this sample, correcting for age/sex distributions and the likelihood of a person being selected for the survey out of their household. Detailed information on the questionnaire, survey methodology and weighting procedures has been provided previously. These data are compared with the data from the 1998 survey to provide information about recent trends in cannabis use in the 14-19 year old population. Statistical analysis A secondary analysis was performed on the data using SPSS. The analysis included the calculation of weighted prevalence estimates for both 1998 and 1995 data. Confidence intervals (CIs) for the main prevalence estimates of cannabis availability, ever use and past year use in the total adolescent population, are provided in Table 1. Approximate effective sample sizes (ESS; the actual sample size divided by the design effect) were used when conducting statistical tests on the weighted estimates16 (1998 ESS=598; 1995 ESS=175). In order to examine age and gender AUSTRALIAN AND NEW ZEALAND JOURNAL OF PUBLIC HEALTH Reid, Lynskey and Copeland Table 1: 1998 and 1995 prevalence of adolescent lifetime cannabis use, recent cannabis use and opportunity to use cannabis, by gender and age group. % offered cannabis last year Female Male 1998 Age 14-15 16-17 18-19 Total 1998 (95% CI) 1995 Age 14-15 16-17 18-19 Total 1995 (95% CI) 31.8 54.1 53.4 36.8 54.6 52.9 % ever used cannabis Female Male % used cannabis last year Female Male 47.8 (43.8-51.8) 29.0 35.7 54.0 31.6 44.2 56.3 45.2 (41.2-49.2) 13.2 18.7 42.9 26.0 55.0 57.0 35.1 (31.3-38.9) 11.6 14.8 35.7 21.7 44.1 45.0 41.7 (34.4-49.0) 35.5 (28.4-42.6) 28.7 (16.2-41.2) differences in cannabis use indicators, a series of logistic regressions were conducted on 1998 data which included gender and age as predictor variables. Trends in these indicators across survey years were assessed by another series of logistic regressions, conducted on combined 1995 and 1998 data, which included data year, sex and an interaction variable in the models. The odds ratio (OR) and 95% CI for each predictor was calculated. Chi-square analyses were conducted to examine frequency data and differences between categories of use groups, and t-tests were performed on the SF-36 scores. Results Prevalence of cannabis use Table 1 presents the proportion of adolescents in 1998 who had been offered or had the opportunity to use cannabis in the past year, who had used it at least once in their lifetime, and who had used it at least once in the past year, by age and gender. The results indicate that cannabis is widely available, with nearly half (47.8%) of the 14-19 year old population offered cannabis or given the opportunity to use it in the preceding year. Logistic regression analyses revealed that cannabis availability in the past year did not differ among males (48.3%) and females (47.2%), [OR=1.03 (0.74-1.44), not significant (ns)]. However, access to cannabis significantly increased with age [OR=1.23 (1.10–1.36), p< 0.001] from 35% of 14-15 year olds to 54% of 16-19 year olds. Approximately 45% of 14-19 year olds had used cannabis at least once in their lifetime, and approximately 78% of that group (or 35% of the adolescent population) used it in the past year. Separate logistic regression analyses were conducted to examine age and gender differences in each indicator. No gender differences were present in either lifetime [OR=0.98 (0.70-1.39), ns] or past year use [OR=1.17 (0.64-2.14), ns]. The prevalence of lifetime cannabis use significantly increased with age throughout adolescence [OR=1.50 (1.35-1.68), p<0.001]: 24.7% of 1415 year olds, 47.3% of 16-17 year olds and 62.7% of 18-19 year olds had used cannabis. Similarly, past year use also significantly increased with age [OR=0.70 (0.56–0.88), p<0.005] and, as expected, the prevalence of past year use was lower than lifetime use, particularly among older adolescents. The mean age of first cannabis use was 14.6 years, a similar result to the mean age of first use in 1995, which was 14.8 years, (t=0.82 (df=371), ns). The 1995 estimates of the prevalence of opportunity to use, lifetime use and past year use are shown with the 1998 data in Table 1. Access to cannabis rose slightly from 39.4% to 47.2% among female adolescents, and from 43.6% to 48.3% among males, although logistic regression analyses found no significant main effect of year on access [OR = 1.56 (0.51–4.78), ns], nor was there a significant interaction between year and gender [OR = 0.88 (0.44-1.75), ns]. A larger increase occurred in lifetime cannabis use: in 1995, 35.5% of 14-19 year olds had used cannabis, and this significantly increased to 45.2% in 1998 [OR=6.37 (1.89-21.74), p<0.005]. A significant interaction was found between year and gender [OR=0.40 (0.19-0.83), p<0.015], indicating that this increase was not equal among male and female adolescents. Table 1 shows that the proportion of adolescent males who had ever used cannabis remained fairly stable (44.7% in 1995 and 45.3% in 1998), while the proportion of females who had used cannabis almost doubled from 24.4% in 1995 to 45.2% in 1998. Therefore, while in previous years males were more likely than females to have used cannabis at least once in their lifetime, recent trends have removed this gender difference. The prevalence of past year cannabis use among adolescent females also increased from 20.1% to 34.6% with no change in prevalence among males (35.9% in 1995 and 35.6% in 1998). However, neither year [OR=0.41 (0.036.62), ns] nor the interaction between year and gender [OR=1.48 (0.30-7.25), ns] was found to be significant in predicting past year use. Frequency of cannabis use Information on the extent or frequency of cannabis use among the group of 14-19 year olds who have used cannabis at least 2000 VOL. 24 NO. 6 AUSTRALIAN AND NEW ZEALAND JOURNAL OF PUBLIC HEALTH Cannabis use among Australian adolescents % of M & F lifetime users who are currently using at each frequency 40 35 30 25 20 15 10 5 0 Don't currently use 1-2 times per year or less often Figure 1: 1998 frequency of adolescent cannabis use by gender. once is presented by gender in Figure 1. Figure 1 shows that a large proportion of adolescents who had used cannabis did so infrequently or had stopped using the drug: over one third (37.5%) of young people who had used cannabis did not currently use, and 16.9% only used cannabis 1-2 times per year or less often. A further 24.8% of cannabis users used the drug monthly or less, while a minority (20.8% of cannabis users or 9.4% of the whole adolescent population) used it on a weekly basis or even more frequently, including every day. Daily use (at least once a day) was reported by 7.1% of cannabis users. An overall chi-square test indicated that no significant age differences in the frequency of use were present (χ2 (df=8) = 12.77, ns). An overall chi-square test was also conducted to examine gender differences in frequency of use, which approached significance (χ2 (df=4) = 9.28, p=0.055, ns). Figure 1 shows that within the frequency category ‘weekly to a few times weekly’ (excluding daily), there were more males (19.9% of males who had used cannabis) than females (7.7% of females who had used cannabis). An overall chi-square test of the difference in 1995 and 1998 frequency patterns was not significant (χ2 (df=4) = 5.08, ns). However, given the rise in lifetime use among females, it was of interest to examine differences in intensity across survey years among females. Although caution is warranted due to the small 1995 sample size, the proportion of females who had used cannabis in the past but did not currently use has increased from 18.3% in 1995 to 37.1% in 1998. This suggests that a large proportion of this new group of female adolescents who have used cannabis appear not to have continued using the drug or progressed to heavy use within this time frame. usually obtained the drug from a friend or acquaintance (86.3% of current users). The much smaller proportion of current users who usually obtained it from a street dealer increased with age, from 4.5% of those aged 14-15 to 9.7% of those aged 18-19 years. Most common method of using cannabis The majority of Australian adolescents who had used cannabis in the past year smoked it most commonly from a bong or pipe (77.5%), while a smaller number commonly used joints (21.6%). Type of cannabis commonly used The forms of cannabis most commonly used among adolescents who had used it in the past year were heads (47.9%) and leaf (28.8%). A surprising proportion (19.7%) reported that they usually used ‘skunk’ (it is not known how accurately users are able to differentiate skunk from other forms of cannabis).20 Very few reported that they usually used other forms of cannabis (such as hash). Location where cannabis is used Respondents who reported current use of cannabis were asked to describe all the locations in which they used it. Cannabis was used in a variety of locations, but the most usual places were at a friend’s home (80.5% of current users), at parties (69.6%) and in their own home (42.0%). Cannabis use also occurred relatively frequently in public places (33.3%) such as parks and in cars or other vehicles (21.6%). A little more than 1 in 10 school-aged current users (i.e. 14-17 years old) had used cannabis at school, or at other educational institutions. Drug of choice All respondents were asked to indicate their favourite or preferred drug. Despite the high prevalence of cannabis use, only 7.4% of all adolescents (and only 14.9% of those who had used cannabis) had a preference for that drug. The majority, 43.4% of the adolescent population (or 48.9% of cannabis users), preferred to drink alcohol. Another 11.2% of adolescents (or 18.4% of cannabis users) preferred to use tobacco. Context of cannabis use Where cannabis is obtained The most common way in which adolescents first obtained cannabis was via a friend or acquaintance (84.7% of those that have used cannabis in their lifetime). Very few young people first obtained cannabis from a street dealer (3.0%) or sexual partner (3.5% of female cannabis users). Most current cannabis users also 2000 VOL. 24 NO. 6 AUSTRALIAN AND NEW ZEALAND JOURNAL OF PUBLIC HEALTH Reid, Lynskey and Copeland Table 2: Prevalence of tobacco, alcohol and other illicit drug use among non-users, light cannabis users and regular cannabis users aged 14-19 years. Other drug use Never used cannabis Use less than monthly or no longer use Use monthly or more often % smoked more than 100 cigarettes in lifetime % currently smoking daily % drinking alcohol at least 1 day/week % females drinking at least 5 drinks in a session in past 2 weeks % males drinking at least 7 drinks in a session in past 2 weeks % reporting other illicit drug usea Notes: (a) The term ‘illicit drug use’ includes use of amphetamines, ecstasy, LSD and other hallucinogens, cocaine, methadone and heroin. Use of other substances Prevalence of other substance use among cannabis users Cannabis use and SF-36 Health Scores Figure 2 displays the magnitude of difference in mean-scaled scores between those young people who used cannabis at least monthly (regular users) and those who used less often or not at all, on the eight dimensions of the SF-36. A higher-scaled score indicates better health: light/non-users had higher mean-scaled scores than the regular users on all dimensions. T-tests were conducted for scores on each dimension. Scores on the general health (t=-4.96, df=587, p<0.001) and vitality (t= -4.12, df=589, p<0.001) dimensions were significantly lower for monthly (or higher frequency) users than for lighter or non-users. While these findings indicate that regular cannabis use among 14-19 year olds may be associated with poorer health than less frequent cannabis use or none at all, the nature of this association is complex. It is important to note that the results are not an estimate of the health impact of cannabis use. Adolescents who had not used cannabis were compared with those who no longer used or used infrequently, and those who used regularly, on several measures of tobacco and alcohol use and also on a single measure of any illicit drug use. These comparisons of substance use patterns are summarised in Table 2, which shows that cannabis users were consistently much more likely to have used tobacco and alcohol frequently, engaged in binge-drinking behaviour and used other illicit substances. Chisquared tests of the association between lifetime cannabis use and each of these drug use behaviours were all highly significant (p<0.001). Table 2 also shows that participation in these behaviours is associated with the extent of cannabis use. Adolescents who used cannabis regularly (monthly or more often) were more likely to report all of these behaviours than adolescents who used less frequently. Compared to non-users, regular users were approximately 18 times more likely to be current daily smokers and 63 times more likely to have reported other illicit drug use. Female regular users were approximately seven times more likely than female non-users to report recently drinking at least five drinks in one session, and male regular users were eight times more likely than male non-users to report recently drinking at least seven drinks in one session. Discussion Findings from the 1998 National Drug Strategy Household Survey indicate that cannabis is widely available to adolescents, despite its illegal status. Approximately 45% of 14-19 year olds have used cannabis at least once in their lifetime, and approximately 35% used the drug in the previous 12 months. The prevalence of this behaviour suggests that it is almost normative, especially among older adolescents. While there were clear age differences in use, there were no gender differences in the prevalence of cannabis use. A substantial increase had occurred in the number of young females who had tried cannabis over the past few years, while the number of males had remained stable. This pattern deviates from the traditional norm, in which males were more likely to use cannabis at all levels of intensity. The change in prevalence among female adolescents does not appear to be due merely to changes in the availability of cannabis, as the increase in availability of cannabis among young females was smaller than the change in prevalence and was not significant. The trend may be reflective of changing gender roles among this generation of adolescents,22 in combination with a general trend towards increased cannabis use among all age groups. For example, the proportion of the overall Australian 2000 VOL. 24 NO. 6 Concurrent use of alcohol and cannabis Most adolescents (72.0%) who had used cannabis in the past year used it in conjunction with alcohol on at least one occasion in that period. Significant age differences exist in the prevalence of this behaviour (χ2 (df=2) = 19.48, p<0.005): 46.2% of 14-15 year olds who had used cannabis in the past year, increasing to 82.2% and 74.3% of adolescents in the 16-17 and 18-19 age brackets, respectively. Although this question does not reveal the amount of alcohol that was used when respondents used cannabis, the prevalence of this behaviour is of considerable importance because alcohol is known to intensify the health and behavioural effects of cannabis.21 AUSTRALIAN AND NEW ZEALAND JOURNAL OF PUBLIC HEALTH Cannabis use among Australian adolescents General health Vitality Mental health Bodily pain Role Emotion Social functioning Role Phys Phys functioning 0 2 Figure 2: Magnitude of difference in mean SF-36 sores for monthly cannabis users and lighter/non-users aged 14-19. population aged 14 years and over who have used cannabis has also increased from approximately 31% in 1995 to 39% in 1998.23 It is also possible that community debate concerning cannabis and changes to its legal status in some Australian jurisdictions may be especially influential among women. Gomberg (1982) suggested that women might be more law-abiding than men, and that there was more stigma attached to women who use illegal street drugs.24 The promotion of cannabis as a socially acceptable and harmless drug could be expected to reduce the stigma previously associated with cannabis use for females. Changes in rates of cannabis use among young females, and a lack of consistent gender differences were also reported in a recent German study of adolescent cannabis use,25 suggesting that the pattern reported here may reflect a developing international trend. Many young people who have used cannabis (54% of those reporting lifetime use) appear to have stopped using it, or have been using the drug infrequently (1-2 times per year). This suggests that the high rate of lifetime cannabis use reflects a large amount of experimental and irregular use that does not necessarily progress to regular or heavy use. However, longitudinal data is needed to verify this suggestion, as Perkonigg (1999) found that approximately 75% of adolescents who had used cannabis 2-4 times in the preceding year at baseline had used more regularly (five or more times) at follow up.25 Of concern was that a minority (9.4% of all adolescents) had been using cannabis on a weekly basis or more often, including every day. Despite the equal numbers of young males and females who have tried cannabis, there appears to be slight gender differences among frequent users, with more males using weekly to a few times weekly. The frequency of cannabis use among young females should be monitored in the future, as frequent use may also become more common in this group. Contrary to images sometimes portrayed in the media, cannabis is usually obtained via friends or acquaintances, not from street 2000 VOL. 24 NO. 6 dealers. This diffuse supply network has implications for the policing of cannabis legislation, because it makes supply and distribution more difficult to control. Cannabis is used in a variety of locations, but most commonly at a friend’s place or parties. It appears to be used in the same social scene as that in which alcohol is used, as a large number of adolescents who have used it in the past year have used alcohol and cannabis at the same time. In fact, relatively few adolescents have a preference for using cannabis and a large number would rather use alcohol or tobacco. Reducing the concurrent use of alcohol and cannabis might be a useful harm minimisation strategy, particularly as the present findings regarding other substance use indicate that adolescents who have used cannabis are more likely than non-users to drink in large amounts. The present data demonstrate strong associations between the extent of cannabis use and regular/heavy tobacco and alcohol use, and the lifetime use of any other illicit drug. Recent research has also found that a major predictor of the progression of cannabis use after initiation was a history of nicotine dependence and alcohol use disorder.26 Associations between different substance use behaviours and other risk behaviours (such as poor school achievement and attendance, early or risky sexual activity, and early pregnancy) are well-known in the risk behaviour literature.27 The co-occurrence of adolescent risk behaviours suggests a need to develop broad prevention strategies that focus on a range of behavioural issues, rather than concentrating on a single behaviour such as cannabis use. The associations found between regular cannabis use, and lower scores on the general health and vitality dimensions of the SF-36, highlight this need for broad-based strategies. There may also be a need to address specific cannabisrelated problems that may be experienced by the 7.1% of cannabis users who reported daily cannabis use. Given that Kandel and Davies (1992) estimated the risk of DSM-III dependence among AUSTRALIAN AND NEW ZEALAND JOURNAL OF PUBLIC HEALTH Reid, Lynskey and Copeland near daily cannabis users at one in three,12 some members of this group may have developed abuse and dependence disorders, and others are at high risk. These adolescents may require some form of intervention. However, the relatively recent recognition of the dependence potential of cannabis has led to a lack of available treatment options or resources for adolescents with cannabis problems. Awareness of the possible need to make resources available for this group is even more important when it is considered that household surveys may under-estimate the prevalence of heavy cannabis use. Homeless and incarcerated persons are not included in the NDS household surveys, yet this group of young people have particularly high rates of substance use and substance use disorders, including cannabis dependence.28 The NDS household surveys also have some other general limitations. First, the validity and reliability of drug use estimates based on self-report may be affected by the illicit nature of the behaviour in question and the consequences and social implications of this behaviour. For instance, it appeared that adolescents in the 1998 survey were less likely to report substance use if their parents were present at the interview, and somewhat more likely if friends or peers were present at the interview.16 Second, efforts to improve the 1998 survey may have slightly reduced the comparability between the 1995 and the 1998 datasets. For example, the introduction of the split-sample design and the treatment of missing/contradictory responses may have created some systematic biases, albeit small.23 Despite these difficulties, at present the NDS household surveys are one of the most valuable instruments available to monitor adolescent drug use in Australia. The data presented here may assist the planning of public health strategies aimed at reducing adolescent drug use and associated harms by providing a clearer picture of contemporary trends in cannabis use. It will be important to continue monitoring these trends in the future. http://www.deepdyve.com/assets/images/DeepDyve-Logo-lg.png Australian and New Zealand Journal of Public Health Wiley

Cannabis use among Australian adolescents: findings of the 1998 National Drug Strategy Household Survey

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Wiley
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Copyright © 2000 Wiley Subscription Services, Inc., A Wiley Company
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1326-0200
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1753-6405
DOI
10.1111/j.1467-842X.2000.tb00523.x
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Abstract

context and recent trends in cannabis use among Australian adolescents. Amanda Reid, Michael Lynskey and Jan Copeland National Drug and Alcohol Research Centre, University of New South Wales Method: Data was collected from 1,581 adolescents aged 14-19 years as part of the 1998 National Drug Strategy Household Survey, and comparisons were made with data from 350 adolescents who participated in the 1995 survey. Results: Among 14-19 year olds, 47.8% have had the opportunity to use cannabis in the past year and 45.2% have used cannabis at least once in their lifetime. Substantial increases have occurred since 1995 in the prevalence of use among young females. While most cannabis use was fairly infrequent, a minority of 14-19 year olds (9.4%) used cannabis at least weekly. Cannabis use was associated with regular tobacco and alcohol use, and other illicit drug use. Regular cannabis users had lower levels of health on the general health and vitality dimensions of the SF-36. Implications: These results show that cannabis availability and use is common among Australian adolescents, and confirm that there has been an increase in use between 1995 and 1998, although only among young females. Future research is required to understand why this recent increase has occurred, and trends in cannabis uptake and use patterns among this group should be carefully monitored. Interventions may need to be developed and made available to the group of young people who are using cannabis heavily. (Aust N Z J Public Health 2000; 24: 596-602) annabis is the most commonly used illicit drug in Australia and internationally. 1-2 Prevalence of use among Australian adolescents has increased over the past decade,3 with 36% of Australian secondary school students aged 12-17 years reporting cannabis use in 1996. 4 Recent media reports of cannabis-related school expulsions have highlighted community concern about the high rate of cannabis use by adolescents and the possible physical and psycho-social consequences of use. Research suggests that cannabis use may be associated with a variety of negative effects, such as impaired educational performance, initiation into other illicit drug use and adverse mental health.3 The patterns of heaviest cannabis use are likely to occur during late adolescence and early adulthood, increasing the risk of harmful acute effects and the potential for abuse and dependence.5 Adolescents have been found to be at greater risk of cannabis dependence than adults for a given dose.6 Earlier onset of substance use could also increase the risk of developing later substance-related problems.7-9 Previous studies on the prevalence of adolescent cannabis use have found marked age and gender differences. The prevalence of cannabis use has consistently been found to increase with age during adolescence1,3 and higher rates of cannabis use have been found among males across all age-groups. 3,10 Heavy use patterns are also more common among males.11-12 Although successive studies estimating the prevalence of lifetime use have documented an increase in use, the most recent estimates available are based on data collected during the 1996 Australian School Students’ Alcohol and Drugs Survey.4 This is the only national survey of school students that has been conducted, and there are problems in comparing the results of this national survey with those of previous regionally based school surveys. School surveys are also limited by the difficulties in generalising results to the wider adolescent population, as research has shown that adolescents who are out of school are more likely to engage in drug use.13 Therefore, the increase in cannabis use among the adolescent population is difficult to confirm and quantify, despite the importance of monitoring this trend. Additionally, the nature of the progression of this trend in the past few years is unknown. More recent data on the prevalence of adolescent cannabis use was collected during the 1998 National Drug Strategy Household Survey (NDSHS).14 This survey was the sixth in a series of household surveys on tobacco, alcohol and illicit drug use that have been conducted since 1985. Trends in the prevalence of adolescent cannabis use over the past few years can be more precisely determined using data from this survey series. A further benefit of the 1998 NDSHS is that it provides comprehensive data on the context of cannabis use and includes the SF-36 health questionnaire.17 This paper presents an analysis of the 1998 NDSHS data, and aims to estimate the prevalence of lifetime and recent cannabis use among Australian adolescents (aged 14-19 years) and to describe the frequency and context of cannabis use in this population. A further aim is to examine recent trends in the prevalence of cannabis use by comparing the Submitted: February 2000 Revision requested: August 2000 Accepted: November 2000 Correspondence to: Amanda Reid, National Drug and Alcohol Research Centre, University of New South Wales, Sydney, New South Wales 2052. Fax: (02) 9399-7143; e-mail: A.Reid@unsw.edu.au AUSTRALIAN AND NEW ZEALAND JOURNAL OF PUBLIC HEALTH 2000 VOL. 24 NO. 6 Cannabis use among Australian adolescents 1998 data with data from the 1995 survey wave.15 This paper also reports the associations between cannabis use, other illicit drug use and regular tobacco/alcohol use, and the associations between cannabis use and scores on the SF-36 health questionnaire. Method The 1998 National Drug Strategy Household Survey The 1998 survey was conducted by Roy Morgan Research and managed by the Australian Institute of Health and Welfare. Data were collected in the period July to mid-September 1998. A sample of 1,581 adolescents (823 females and 758 males) aged 14-19 years took part, constituting 15.8% of the total survey sample (n=10,340). The sampling procedure was designed to provide a near random sample of households within each specified geographic region across Australia. Three sampling methods were used. Sample 1 interviews were conducted in the respondent’s home, using a mixture of face-to-face interview combined with a confidential, sealed, self-completion questionnaire for sensitive sections (such as personal drug use behaviour). Eligible households were those containing at least one person aged 14 or over, and selection of the respondent was based on whose birthday next occurred. Sample 2 questionnaires were completed in the same households as Sample 1, by the youngest person aged 14 and over who had not been interviewed in Sample 1. Sample 2 completed an entirely self-administered questionnaire. Sample 3 questionnaires were completed by those aged 14-39 years in capital cities only, and again were entirely selfadministered. The data presented here are based on the combined three samples, since few significant differences were found between the samples in respect to drug use.16 Biased sampling towards the young and those living in capital cities contributed to specific differences between the combined sample and the known demographics of the Australian population. These differences were addressed by using weighted data to derive population estimates. In the final weighted combined sample, all regions and age/gender groups were represented in their correct proportions. The estimated overall response rate (for all three samples combined) was 56%, and was similar to previous waves of this survey. More detailed information regarding sampling methodology and design, response rates, derivation of weights and design effects can be found in the NDSHS: Technical Report 1998.16 The questionnaire included questions on a range of topics including drug-related knowledge, attitudes, use and behaviours relevant to alcohol, tobacco and a range of illicit drugs. However, only the data relevant to cannabis and correlates of its use are reported in this paper, and the specific questions relating to these areas are described below. Cannabis – Extent of cannabis use and associated behaviours were measured by a series of questions that were filtered 2000 VOL. 24 NO. 6 according to response. Respondents were asked if they had been offered or had the opportunity to use marijuana in the past 12 months, and in a separate section, if they had ever tried marijuana. If they had tried cannabis, they were questioned about age and circumstances of first use, asked if they had used marijuana in the past 12 months, and questioned about frequency of current use. If respondents had used cannabis in the past 12 months, they were asked additional questions on patterns of use. Tobacco, alcohol and other illicit drug use – Respondents were asked screening questions about their tobacco and alcohol use. If respondents had smoked a full cigarette in their lifetime, they were asked if they had smoked at least 100 cigarettes or the equivalent amount of tobacco in their life, and if they were currently smoking daily. Similarly, if respondents had consumed a full glass of alcohol in their lifetime, they were asked how often they had an alcoholic drink of any kind. Along with this measure of frequency, incidences of recent binge-drinking were obtained. A measure of any other illicit substance use was obtained by combining data collected individually for a number of illicit drugs. All respondents were also questioned about their favourite or preferred substances. Health status – The SF-36 (Short-Form 36) is a self-report questionnaire containing 36 items which measure health-related quality of life.17 The Australian version of this questionnaire (see Sanson-Fisher and Perkins (1998) for a description of psychometric performance) was included in the 1998 survey.18 The 1995 National Drug Strategy Household Survey The 1995 survey was conducted by AGB McNair. Data were collected over the months of May and June 1995. A sample of 350 adolescents (201 males, 149 females) aged between 14 and 19 years (9% of the total sample) completed the interviews. A single sample design was used. All respondents completed a confidential sealed section, along with a separate, intervieweradministered questionnaire. The total sample response rate was 57% of the households actually contacted. Person-specific weights were also calculated for this sample, correcting for age/sex distributions and the likelihood of a person being selected for the survey out of their household. Detailed information on the questionnaire, survey methodology and weighting procedures has been provided previously. These data are compared with the data from the 1998 survey to provide information about recent trends in cannabis use in the 14-19 year old population. Statistical analysis A secondary analysis was performed on the data using SPSS. The analysis included the calculation of weighted prevalence estimates for both 1998 and 1995 data. Confidence intervals (CIs) for the main prevalence estimates of cannabis availability, ever use and past year use in the total adolescent population, are provided in Table 1. Approximate effective sample sizes (ESS; the actual sample size divided by the design effect) were used when conducting statistical tests on the weighted estimates16 (1998 ESS=598; 1995 ESS=175). In order to examine age and gender AUSTRALIAN AND NEW ZEALAND JOURNAL OF PUBLIC HEALTH Reid, Lynskey and Copeland Table 1: 1998 and 1995 prevalence of adolescent lifetime cannabis use, recent cannabis use and opportunity to use cannabis, by gender and age group. % offered cannabis last year Female Male 1998 Age 14-15 16-17 18-19 Total 1998 (95% CI) 1995 Age 14-15 16-17 18-19 Total 1995 (95% CI) 31.8 54.1 53.4 36.8 54.6 52.9 % ever used cannabis Female Male % used cannabis last year Female Male 47.8 (43.8-51.8) 29.0 35.7 54.0 31.6 44.2 56.3 45.2 (41.2-49.2) 13.2 18.7 42.9 26.0 55.0 57.0 35.1 (31.3-38.9) 11.6 14.8 35.7 21.7 44.1 45.0 41.7 (34.4-49.0) 35.5 (28.4-42.6) 28.7 (16.2-41.2) differences in cannabis use indicators, a series of logistic regressions were conducted on 1998 data which included gender and age as predictor variables. Trends in these indicators across survey years were assessed by another series of logistic regressions, conducted on combined 1995 and 1998 data, which included data year, sex and an interaction variable in the models. The odds ratio (OR) and 95% CI for each predictor was calculated. Chi-square analyses were conducted to examine frequency data and differences between categories of use groups, and t-tests were performed on the SF-36 scores. Results Prevalence of cannabis use Table 1 presents the proportion of adolescents in 1998 who had been offered or had the opportunity to use cannabis in the past year, who had used it at least once in their lifetime, and who had used it at least once in the past year, by age and gender. The results indicate that cannabis is widely available, with nearly half (47.8%) of the 14-19 year old population offered cannabis or given the opportunity to use it in the preceding year. Logistic regression analyses revealed that cannabis availability in the past year did not differ among males (48.3%) and females (47.2%), [OR=1.03 (0.74-1.44), not significant (ns)]. However, access to cannabis significantly increased with age [OR=1.23 (1.10–1.36), p< 0.001] from 35% of 14-15 year olds to 54% of 16-19 year olds. Approximately 45% of 14-19 year olds had used cannabis at least once in their lifetime, and approximately 78% of that group (or 35% of the adolescent population) used it in the past year. Separate logistic regression analyses were conducted to examine age and gender differences in each indicator. No gender differences were present in either lifetime [OR=0.98 (0.70-1.39), ns] or past year use [OR=1.17 (0.64-2.14), ns]. The prevalence of lifetime cannabis use significantly increased with age throughout adolescence [OR=1.50 (1.35-1.68), p<0.001]: 24.7% of 1415 year olds, 47.3% of 16-17 year olds and 62.7% of 18-19 year olds had used cannabis. Similarly, past year use also significantly increased with age [OR=0.70 (0.56–0.88), p<0.005] and, as expected, the prevalence of past year use was lower than lifetime use, particularly among older adolescents. The mean age of first cannabis use was 14.6 years, a similar result to the mean age of first use in 1995, which was 14.8 years, (t=0.82 (df=371), ns). The 1995 estimates of the prevalence of opportunity to use, lifetime use and past year use are shown with the 1998 data in Table 1. Access to cannabis rose slightly from 39.4% to 47.2% among female adolescents, and from 43.6% to 48.3% among males, although logistic regression analyses found no significant main effect of year on access [OR = 1.56 (0.51–4.78), ns], nor was there a significant interaction between year and gender [OR = 0.88 (0.44-1.75), ns]. A larger increase occurred in lifetime cannabis use: in 1995, 35.5% of 14-19 year olds had used cannabis, and this significantly increased to 45.2% in 1998 [OR=6.37 (1.89-21.74), p<0.005]. A significant interaction was found between year and gender [OR=0.40 (0.19-0.83), p<0.015], indicating that this increase was not equal among male and female adolescents. Table 1 shows that the proportion of adolescent males who had ever used cannabis remained fairly stable (44.7% in 1995 and 45.3% in 1998), while the proportion of females who had used cannabis almost doubled from 24.4% in 1995 to 45.2% in 1998. Therefore, while in previous years males were more likely than females to have used cannabis at least once in their lifetime, recent trends have removed this gender difference. The prevalence of past year cannabis use among adolescent females also increased from 20.1% to 34.6% with no change in prevalence among males (35.9% in 1995 and 35.6% in 1998). However, neither year [OR=0.41 (0.036.62), ns] nor the interaction between year and gender [OR=1.48 (0.30-7.25), ns] was found to be significant in predicting past year use. Frequency of cannabis use Information on the extent or frequency of cannabis use among the group of 14-19 year olds who have used cannabis at least 2000 VOL. 24 NO. 6 AUSTRALIAN AND NEW ZEALAND JOURNAL OF PUBLIC HEALTH Cannabis use among Australian adolescents % of M & F lifetime users who are currently using at each frequency 40 35 30 25 20 15 10 5 0 Don't currently use 1-2 times per year or less often Figure 1: 1998 frequency of adolescent cannabis use by gender. once is presented by gender in Figure 1. Figure 1 shows that a large proportion of adolescents who had used cannabis did so infrequently or had stopped using the drug: over one third (37.5%) of young people who had used cannabis did not currently use, and 16.9% only used cannabis 1-2 times per year or less often. A further 24.8% of cannabis users used the drug monthly or less, while a minority (20.8% of cannabis users or 9.4% of the whole adolescent population) used it on a weekly basis or even more frequently, including every day. Daily use (at least once a day) was reported by 7.1% of cannabis users. An overall chi-square test indicated that no significant age differences in the frequency of use were present (χ2 (df=8) = 12.77, ns). An overall chi-square test was also conducted to examine gender differences in frequency of use, which approached significance (χ2 (df=4) = 9.28, p=0.055, ns). Figure 1 shows that within the frequency category ‘weekly to a few times weekly’ (excluding daily), there were more males (19.9% of males who had used cannabis) than females (7.7% of females who had used cannabis). An overall chi-square test of the difference in 1995 and 1998 frequency patterns was not significant (χ2 (df=4) = 5.08, ns). However, given the rise in lifetime use among females, it was of interest to examine differences in intensity across survey years among females. Although caution is warranted due to the small 1995 sample size, the proportion of females who had used cannabis in the past but did not currently use has increased from 18.3% in 1995 to 37.1% in 1998. This suggests that a large proportion of this new group of female adolescents who have used cannabis appear not to have continued using the drug or progressed to heavy use within this time frame. usually obtained the drug from a friend or acquaintance (86.3% of current users). The much smaller proportion of current users who usually obtained it from a street dealer increased with age, from 4.5% of those aged 14-15 to 9.7% of those aged 18-19 years. Most common method of using cannabis The majority of Australian adolescents who had used cannabis in the past year smoked it most commonly from a bong or pipe (77.5%), while a smaller number commonly used joints (21.6%). Type of cannabis commonly used The forms of cannabis most commonly used among adolescents who had used it in the past year were heads (47.9%) and leaf (28.8%). A surprising proportion (19.7%) reported that they usually used ‘skunk’ (it is not known how accurately users are able to differentiate skunk from other forms of cannabis).20 Very few reported that they usually used other forms of cannabis (such as hash). Location where cannabis is used Respondents who reported current use of cannabis were asked to describe all the locations in which they used it. Cannabis was used in a variety of locations, but the most usual places were at a friend’s home (80.5% of current users), at parties (69.6%) and in their own home (42.0%). Cannabis use also occurred relatively frequently in public places (33.3%) such as parks and in cars or other vehicles (21.6%). A little more than 1 in 10 school-aged current users (i.e. 14-17 years old) had used cannabis at school, or at other educational institutions. Drug of choice All respondents were asked to indicate their favourite or preferred drug. Despite the high prevalence of cannabis use, only 7.4% of all adolescents (and only 14.9% of those who had used cannabis) had a preference for that drug. The majority, 43.4% of the adolescent population (or 48.9% of cannabis users), preferred to drink alcohol. Another 11.2% of adolescents (or 18.4% of cannabis users) preferred to use tobacco. Context of cannabis use Where cannabis is obtained The most common way in which adolescents first obtained cannabis was via a friend or acquaintance (84.7% of those that have used cannabis in their lifetime). Very few young people first obtained cannabis from a street dealer (3.0%) or sexual partner (3.5% of female cannabis users). Most current cannabis users also 2000 VOL. 24 NO. 6 AUSTRALIAN AND NEW ZEALAND JOURNAL OF PUBLIC HEALTH Reid, Lynskey and Copeland Table 2: Prevalence of tobacco, alcohol and other illicit drug use among non-users, light cannabis users and regular cannabis users aged 14-19 years. Other drug use Never used cannabis Use less than monthly or no longer use Use monthly or more often % smoked more than 100 cigarettes in lifetime % currently smoking daily % drinking alcohol at least 1 day/week % females drinking at least 5 drinks in a session in past 2 weeks % males drinking at least 7 drinks in a session in past 2 weeks % reporting other illicit drug usea Notes: (a) The term ‘illicit drug use’ includes use of amphetamines, ecstasy, LSD and other hallucinogens, cocaine, methadone and heroin. Use of other substances Prevalence of other substance use among cannabis users Cannabis use and SF-36 Health Scores Figure 2 displays the magnitude of difference in mean-scaled scores between those young people who used cannabis at least monthly (regular users) and those who used less often or not at all, on the eight dimensions of the SF-36. A higher-scaled score indicates better health: light/non-users had higher mean-scaled scores than the regular users on all dimensions. T-tests were conducted for scores on each dimension. Scores on the general health (t=-4.96, df=587, p<0.001) and vitality (t= -4.12, df=589, p<0.001) dimensions were significantly lower for monthly (or higher frequency) users than for lighter or non-users. While these findings indicate that regular cannabis use among 14-19 year olds may be associated with poorer health than less frequent cannabis use or none at all, the nature of this association is complex. It is important to note that the results are not an estimate of the health impact of cannabis use. Adolescents who had not used cannabis were compared with those who no longer used or used infrequently, and those who used regularly, on several measures of tobacco and alcohol use and also on a single measure of any illicit drug use. These comparisons of substance use patterns are summarised in Table 2, which shows that cannabis users were consistently much more likely to have used tobacco and alcohol frequently, engaged in binge-drinking behaviour and used other illicit substances. Chisquared tests of the association between lifetime cannabis use and each of these drug use behaviours were all highly significant (p<0.001). Table 2 also shows that participation in these behaviours is associated with the extent of cannabis use. Adolescents who used cannabis regularly (monthly or more often) were more likely to report all of these behaviours than adolescents who used less frequently. Compared to non-users, regular users were approximately 18 times more likely to be current daily smokers and 63 times more likely to have reported other illicit drug use. Female regular users were approximately seven times more likely than female non-users to report recently drinking at least five drinks in one session, and male regular users were eight times more likely than male non-users to report recently drinking at least seven drinks in one session. Discussion Findings from the 1998 National Drug Strategy Household Survey indicate that cannabis is widely available to adolescents, despite its illegal status. Approximately 45% of 14-19 year olds have used cannabis at least once in their lifetime, and approximately 35% used the drug in the previous 12 months. The prevalence of this behaviour suggests that it is almost normative, especially among older adolescents. While there were clear age differences in use, there were no gender differences in the prevalence of cannabis use. A substantial increase had occurred in the number of young females who had tried cannabis over the past few years, while the number of males had remained stable. This pattern deviates from the traditional norm, in which males were more likely to use cannabis at all levels of intensity. The change in prevalence among female adolescents does not appear to be due merely to changes in the availability of cannabis, as the increase in availability of cannabis among young females was smaller than the change in prevalence and was not significant. The trend may be reflective of changing gender roles among this generation of adolescents,22 in combination with a general trend towards increased cannabis use among all age groups. For example, the proportion of the overall Australian 2000 VOL. 24 NO. 6 Concurrent use of alcohol and cannabis Most adolescents (72.0%) who had used cannabis in the past year used it in conjunction with alcohol on at least one occasion in that period. Significant age differences exist in the prevalence of this behaviour (χ2 (df=2) = 19.48, p<0.005): 46.2% of 14-15 year olds who had used cannabis in the past year, increasing to 82.2% and 74.3% of adolescents in the 16-17 and 18-19 age brackets, respectively. Although this question does not reveal the amount of alcohol that was used when respondents used cannabis, the prevalence of this behaviour is of considerable importance because alcohol is known to intensify the health and behavioural effects of cannabis.21 AUSTRALIAN AND NEW ZEALAND JOURNAL OF PUBLIC HEALTH Cannabis use among Australian adolescents General health Vitality Mental health Bodily pain Role Emotion Social functioning Role Phys Phys functioning 0 2 Figure 2: Magnitude of difference in mean SF-36 sores for monthly cannabis users and lighter/non-users aged 14-19. population aged 14 years and over who have used cannabis has also increased from approximately 31% in 1995 to 39% in 1998.23 It is also possible that community debate concerning cannabis and changes to its legal status in some Australian jurisdictions may be especially influential among women. Gomberg (1982) suggested that women might be more law-abiding than men, and that there was more stigma attached to women who use illegal street drugs.24 The promotion of cannabis as a socially acceptable and harmless drug could be expected to reduce the stigma previously associated with cannabis use for females. Changes in rates of cannabis use among young females, and a lack of consistent gender differences were also reported in a recent German study of adolescent cannabis use,25 suggesting that the pattern reported here may reflect a developing international trend. Many young people who have used cannabis (54% of those reporting lifetime use) appear to have stopped using it, or have been using the drug infrequently (1-2 times per year). This suggests that the high rate of lifetime cannabis use reflects a large amount of experimental and irregular use that does not necessarily progress to regular or heavy use. However, longitudinal data is needed to verify this suggestion, as Perkonigg (1999) found that approximately 75% of adolescents who had used cannabis 2-4 times in the preceding year at baseline had used more regularly (five or more times) at follow up.25 Of concern was that a minority (9.4% of all adolescents) had been using cannabis on a weekly basis or more often, including every day. Despite the equal numbers of young males and females who have tried cannabis, there appears to be slight gender differences among frequent users, with more males using weekly to a few times weekly. The frequency of cannabis use among young females should be monitored in the future, as frequent use may also become more common in this group. Contrary to images sometimes portrayed in the media, cannabis is usually obtained via friends or acquaintances, not from street 2000 VOL. 24 NO. 6 dealers. This diffuse supply network has implications for the policing of cannabis legislation, because it makes supply and distribution more difficult to control. Cannabis is used in a variety of locations, but most commonly at a friend’s place or parties. It appears to be used in the same social scene as that in which alcohol is used, as a large number of adolescents who have used it in the past year have used alcohol and cannabis at the same time. In fact, relatively few adolescents have a preference for using cannabis and a large number would rather use alcohol or tobacco. Reducing the concurrent use of alcohol and cannabis might be a useful harm minimisation strategy, particularly as the present findings regarding other substance use indicate that adolescents who have used cannabis are more likely than non-users to drink in large amounts. The present data demonstrate strong associations between the extent of cannabis use and regular/heavy tobacco and alcohol use, and the lifetime use of any other illicit drug. Recent research has also found that a major predictor of the progression of cannabis use after initiation was a history of nicotine dependence and alcohol use disorder.26 Associations between different substance use behaviours and other risk behaviours (such as poor school achievement and attendance, early or risky sexual activity, and early pregnancy) are well-known in the risk behaviour literature.27 The co-occurrence of adolescent risk behaviours suggests a need to develop broad prevention strategies that focus on a range of behavioural issues, rather than concentrating on a single behaviour such as cannabis use. The associations found between regular cannabis use, and lower scores on the general health and vitality dimensions of the SF-36, highlight this need for broad-based strategies. There may also be a need to address specific cannabisrelated problems that may be experienced by the 7.1% of cannabis users who reported daily cannabis use. Given that Kandel and Davies (1992) estimated the risk of DSM-III dependence among AUSTRALIAN AND NEW ZEALAND JOURNAL OF PUBLIC HEALTH Reid, Lynskey and Copeland near daily cannabis users at one in three,12 some members of this group may have developed abuse and dependence disorders, and others are at high risk. These adolescents may require some form of intervention. However, the relatively recent recognition of the dependence potential of cannabis has led to a lack of available treatment options or resources for adolescents with cannabis problems. Awareness of the possible need to make resources available for this group is even more important when it is considered that household surveys may under-estimate the prevalence of heavy cannabis use. Homeless and incarcerated persons are not included in the NDS household surveys, yet this group of young people have particularly high rates of substance use and substance use disorders, including cannabis dependence.28 The NDS household surveys also have some other general limitations. First, the validity and reliability of drug use estimates based on self-report may be affected by the illicit nature of the behaviour in question and the consequences and social implications of this behaviour. For instance, it appeared that adolescents in the 1998 survey were less likely to report substance use if their parents were present at the interview, and somewhat more likely if friends or peers were present at the interview.16 Second, efforts to improve the 1998 survey may have slightly reduced the comparability between the 1995 and the 1998 datasets. For example, the introduction of the split-sample design and the treatment of missing/contradictory responses may have created some systematic biases, albeit small.23 Despite these difficulties, at present the NDS household surveys are one of the most valuable instruments available to monitor adolescent drug use in Australia. The data presented here may assist the planning of public health strategies aimed at reducing adolescent drug use and associated harms by providing a clearer picture of contemporary trends in cannabis use. It will be important to continue monitoring these trends in the future.

Journal

Australian and New Zealand Journal of Public Health – Wiley

Published: Dec 1, 2000

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