University of Sydney, Coral Tree Family Service, North Ryde, New South Wales
Department of Paediatrics, Adelaide University and Research & Evaluation Unit, Women's and Children's Hospital, North Adelaide
Centre for Mental Health, NSW Health
Centre for Adolescent Health, Murdoch Children's Research Institute, Melbourne
National Drug and Alcohol Research Centre, University of New South Wales, Sydney, Australia
Correspondence: Joseph M. Rey, Professor of Child and Adolescent Psychiatry, University of Sydney, Coral Tree Family Service, PO Box 142, North Ryde, NSW 1670, Australia. E-mail: jrey{at}mail.usyd.edu.au
Declaration of interest The Commonwealth of Australia funded the survey.
![]() |
ABSTRACT |
---|
![]() ![]() ![]() ![]() ![]() ![]() ![]() ![]() ![]() |
---|
Aims To ascertain the prevalence of cannabis use among Australian adolescents, associations with mental health problems, risk behaviours and service use.
Method Examination of data from a national representative sample of households comprising 1261 adolescents aged 13-17 years. Parents completed a psychiatric interview and questionnaires while adolescents completed questionnaires.
Results One-quarter of the adolescents in the sample had used cannabis. There were no gender differences. Use increased rapidly with age, was more common in adolescents living with a sole parent and was associated with increased depression, conduct problems and health risk behaviours (smoking, drinking) but not with higher use of services.
Conclusions Cannabis use is very prevalent. The association with depression, conduct problems, excessive drinking and use of other drugs shows a malignant pattern of comorbidity that may lead to negative outcomes.
![]() |
INTRODUCTION |
---|
![]() ![]() ![]() ![]() ![]() ![]() ![]() ![]() ![]() |
---|
![]() |
METHOD |
---|
![]() ![]() ![]() ![]() ![]() ![]() ![]() ![]() ![]() |
---|
Instruments
Adolescents completed the Youth Self-Report (YSR;
Achenbach, 1991a), the
Child Health Questionnaire (CHQ; Landgraf
et al, 1996), a self-rating depression scale (the Centre
for Epidemiological Studies Depression (CES-D) scale;
Radloff, 1977) and the Youth
Risk Behaviour Questionnaire (YRBQ; Brener
et al, 1995). Adolescents placed completed questionnaires
in a sealed envelope to ensure confidentiality.
Parents or main caregivers (henceforth described as parents) were interviewed using the parent version of the Diagnostic Interview Schedule for Children, Version IV (DISC-IV; Shaffer et al, 2000). Parents also completed the parent version of the CHQ (Landgraf et al, 1996), the Child Behaviour Checklist (CBCL; Achenbach, 1991b) and an interviewer-administered questionnaire covering demographic and service use information.
Measures
The YRBQ completed by adolescents was employed to determine cannabis use
and other health risk behaviours. The YRBQ has four questions about cannabis
(marijuana) use: "how old were you when you tried marijuana for the
first time?" (categorised as never, 12 and
13 years of age);
"During your life, how many times have you used marijuana?" (0,
1-2, 3-9, 10-19, 20-39, 40-99, >99 times); "During the past 30 days,
how many times did you use marijuana?" (0, 1-2, 3-9, 10-19, 20-39,
>39 times); and "During the past 30 days, how many times did you use
marijuana on school property?" (0, 1-2, 3-9, 10-19, 20-39, >39
times). Other health risk behaviours considered were suicidal thoughts and
suicide attempts during the past year, cigarette smoking (
10 cigarettes
during the previous month), alcohol use (
5 drinks at least once in the
previous month) and use of other drugs (having ever used any other
non-prescribed drug of abuse or inhalants).
Ratings of emotional and behavioural problems according to parents and adolescents were obtained using the CBCL and YSR scales, respectively. The Delinquent Scale of the CBCL and YSR contains one item (no. 105) on substance use. To avoid spurious associations, scores on this scale were computed without item 105. Ratings of depression were obtained from the adolescent using the CES-D.
Diagnoses of DSM-IV (American Psychiatric Association, 1994) attention-deficit hyperactivity disorder (ADHD) and conduct disorder were obtained using the DISC-IV administered to parents. Prevalence of ADHD in adolescents was 7.1% and of conduct disorder was 2.4%.
Depression was considered to be present if either parent or adolescent reported significant depression. A detailed description of the method used is available in Rey et al (2001). In summary, for parents' reports it required meeting the criteria for DSM-IV major depression or dysthymia (DISC-IV interview). For adolescents, this was defined as having clinically significant depression during the previous week (CES-D >20 for males and >22 for females; Roberts et al, 1991) and significant impairment in psychosocial functioning (past 4 weeks) as measured on the CHQ. According to this, 8.2% of participants met the criteria for depression. Demographic and service use data were obtained from parents' interviews.
Statistical analysis
Variables rating demographic characteristics, service use and risk
behaviours were dichotomous or dichotomised for analysis and were examined
using 2 and odds ratios. Alpha was set at 0.05. Reported
percentages are rounded to the nearest unit.
Figure 1 shows depression scores as reported by adolescents (CES-D) according to their severity as low (bottom 50%), medium (next 25%), high (next 15%) and very high (top 10%), computed separately for boys and girls.
|
There were significant associations between many of the independent variables (e.g. between YSR scales). To control for this, the variables that were different between the groups in univariate analyses in Tables 2 and 3 were entered into logistic regression models. Cannabis use (no=0, yes=1) was the dependent variable. When both CES-D scores and scores on the anxious/depressed scale according to the adolescent were different between groups, only CES-D scores were included in the appropriate multivariate analyses. Owing to the large effect of age on cannabis use, age was included in all multivariate analysis.
|
|
Missing data
Overall, 229 adolescents (15%) did not answer questions about cannabis use
and so were not included in any of the analyses. The sample studied therefore
comprised 1261 (85%) of the 1490 participants. A further 101 adolescents (7%)
had missing data on at least one relevant variable; they were not included in
analyses when the missing variable was considered. Participants with any
missing data (n=330, 22%) were no different from those without
missing data in age, family income and diagnosis of depression or ADHD.
However, participants with missing data were less likely to live in an
original two-parent family (68% v. 74%; 2=5.8,
P=0.02) and more likely to be male (56% v. 47%;
2=6.9, P<0.01), to have a diagnosis of conduct
disorder (4% v. 2%;
2=6.2, P<0.05), and
to have been rated by parents as more disturbed overall in the CBCL (mean
total problems=20.8 v. 16.7; t=2.5, P<0.05).
This suggests that adolescents whose results were employed in these analyses
are less disturbed than adolescents whose results were not included.
![]() |
RESULTS |
---|
![]() ![]() ![]() ![]() ![]() ![]() ![]() ![]() ![]() |
---|
|
Of those who used cannabis, 19% used it for the first time at 12 years of age or younger. Males were twice as likely as females to have used cannabis before the age of 13 years (95% CI 1.2-3.8). Cannabis use increased rapidly with age, on average 1.6-fold per year (95% CI 1.49-1.83). Of those who had used cannabis 42% had used it during the previous month. Few (n=20, 6%) had used the drug at school in the previous month.
Emotional and behavioural problems
The mean raw scores on the various CBCL (parent) and YSR (youth) scales and
on the CES-D were compared according to cannabis use in the past month (not at
all, once or twice, three or more times). These data are presented in
Table 2. Those who used
cannabis had more emotional (internalising) and behavioural (externalising)
problems than those who did not. Differences were more marked and widespread
for youth self-reports than for parents' reports but were consistent for
both.
Multivariate analysis (including age, CES-D scores and the narrow-band
syndromes that were significantly different in
Table 2 as predictors) showed
that cannabis use was associated with greater depression (adjusted odds ratio
(OR) 1.03, 95% CI 1.01-1.05), greater delinquent problems (adjusted OR 1.66,
95% CI 1.51-1.82) and lower withdrawn scores (adjusted OR 0.89,
95% CI 0.81-0.98) according to adolescents and with lower attention problem
scores according to parents (adjusted OR 0.93, 95% CI 0.86-0.99) (model
2=364.36, d.f.=10, P<0.001). These odds ratios
refer to an increase of one scale point.
Figure 1 shows a gradual
increase in cannabis use with increasing self-reported depression scores
(CES-D) (males: 2=46.9, d.f.=3, P<0.001; females:
2=52.1, d.f.=3, P<0.001). This association
decreases only slightly after controlling for the effect of age on cannabis
use from OR 1.62 to adjusted OR 1.60 (95% CI 1.40-1.82) for males and OR 1.68
to adjusted OR 1.65 (95% CI 1.44-1.89) for females. That is, females with
depression scores in the top 10% (scores >26 on the CES-D) are five times
more likely to have used cannabis than females with scores in the bottom 50%
(scores <9).
Demography, diagnosis, risk behaviours and use of services
These data are presented in Table
3. Those who had ever used cannabis were less likely to live in an
original, two-parent family and more likely to live with a solo parent.
However, use was not associated with other socio-economic variables such as
parental employment, education or family income.
Depression, attention-deficit hyperactivity disorder (ADHD) and conduct
disorder were the only diagnoses considered in the survey. Adolescents who
qualified for a diagnosis of depression or conduct disorder were more likely
to have used cannabis than those who did not. For example, among the teenagers
who had used cannabis, 14% of the males qualified for a depressive disorder
compared with 6% of those who had not used it (2=9.6,
P<0.01). The parallel figures for females were 18% and 6%
(
2=24.9, P<0.001). There was no association with
ADHD.
Adolescents who reported having used cannabis were much more likely to report drinking alcohol, smoking cigarettes and to have tried other drugs. However, they did not use services more often.
A multiple logistic regression analysis was used to identify the relationship between each independent variable and cannabis use, controlling for the effect of the other independent variables in the model (Table 3). In this analysis, living with a sole parent, cigarette smoking, drinking alcohol, using other drugs and a diagnosis of depression were associated with cannabis use (fourth column, Table 3).
![]() |
DISCUSSION |
---|
![]() ![]() ![]() ![]() ![]() ![]() ![]() ![]() ![]() |
---|
It could be argued that using the house-hold as the contact point may have inhibited adolescents' answers and that these results underestimate cannabis use. Although all care was taken to protect confidentiality (adolescents were instructed to place completed questionnaires in a sealed envelope), some underestimation is likely given that 15% did not answer questions about cannabis use and that participants with missing data were rated by parents as more disturbed overall. Nevertheless, estimates of use of alcohol and cigarettes in this study were comparable with those reported in other Australian surveys, although the age groups and period considered varied slightly. For example, a national survey conducted in 1998 found that 7.2% of females who had never used cannabis reported having had five or more drinks at least once in the previous 2 weeks (Reid et al, 2000), compared with 8.2% who had had five or more drinks at least once in the previous month in the present study. In the Australian state of New South Wales, among secondary school students aged 12-17 years in 1996, 19% of boys and 21% of girls reported having smoked cigarettes during the previous week (Schofield et al, 1998) whereas 45% of each gender reported having ever smoked in the present survey.
Age and gender
There is a strong age effect in the prevalence of cannabis use, with
self-reported lifetime use increasing from 7% among 13-year-olds to 41% among
17-year-olds. This is consistent with the results of previous studies
(Johnston et al,
2000) and confirms that adolescence is the peak age for cannabis
initiation (Chen & Kandel,
1995). Given that age of first use may be an important factor in
determining progression to heavy or problematic use
(DeWit et al, 2000),
such findings raise concerns about the extent to which current levels of use
among adolescents may translate into future problematic use. This is
particularly worrying because estimates suggest that about one in ten of those
who ever used cannabis may develop dependency
(Fergusson & Horwood,
2000; Johns,
2001). However, most seem to use the drug infrequently: more than
50% used fewer than 10 times and 13% used 100 times or more. 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 (Reid et al,
2000).
Prevalence was similar among males (25%) and females (26%). This contrasts with earlier studies reporting strong gender effects, with both the prevalence and frequency of cannabis use being higher among males than females (Hall et al, 1999). These findings confirm recent reports that gender differences in rates of cannabis and other drug use are narrowing as young women increasingly adopt patterns of use that mirror those of their male counterparts (Smith & Rutter, 1995; Perkonigg et al, 1999; Reid et al, 2000). Cannabis use has increased among females at a more rapid pace, resulting in a narrowing of the gender gap. Something similar is occurring with crime and conduct problems (Smith & Rutter, 1995). This also may reflect that cannabis use has become more socially acceptable and destigmatised.
Depression
The association between cannabis use and psychosis has received much
attention (Hall & Degenhardt,
2000). However, links with emotional problems also are relevant.
There are suggestions that depressed individuals are more likely to use
cannabis and that consumption of cannabis is associated with an increase in
anxiety, depression and suicide attempts
(Johns, 2001). In the current
study, an association was found between depression (whether conceptualised as
a categorical diagnosis or as depressed mood) and cannabis use. The
cross-sectional nature of the study does not allow clarification of what comes
first or whether both problems are the result of common aetiological factors.
This will require further examination in prospective studies.
Disruptive behaviour
Cannabis use among teenagers is part of a pattern of wider substance use
(cigarettes, alcohol, other drugs) and conduct problems.
The lack of association with ADHD contrasts with reports of increased substance use among young people with ADHD (Schubiner et al, 2000; Wilens et al, 1997). The results of this survey are consistent with evidence showing that ADHD does not seem to increase the risk of cannabis use, although in this study concurrent ADHD was considered rather than ADHD that clearly preceded drug use. Because substance use is strongly associated with conduct problems, the reported association with ADHD, particularly in clinic samples, may be due to comorbidity between ADHD and problems of conduct (Lynskey & Fergusson, 1995; Chilcoat & Breslau, 1999; Disney et al, 1999).
The association between cannabis use, depression, conduct problems, tobacco smoking, excessive drinking and use of illicit drugs shows a malignant pattern of comorbidity that may lead ultimately to further negative outcomes. Preventing this will require more than health education about drug issues, and it will need close involvement of child and adolescent mental health services.
![]() |
Clinical Implications and Limitations |
---|
![]() ![]() ![]() ![]() ![]() ![]() ![]() ![]() ![]() |
---|
LIMITATIONS
![]() |
ACKNOWLEDGMENTS |
---|
![]() ![]() ![]() ![]() ![]() ![]() ![]() ![]() ![]() |
---|
![]() |
REFERENCES |
---|
![]() ![]() ![]() ![]() ![]() ![]() ![]() ![]() ![]() |
---|
Achenbach, T. M. (1991b) Manual for the Child Behavior Checklist/4-18 and 1991 Profile. Burlington, VT: University of Vermont, Department of Psychiatry.
American Psychiatric Association (1994) Diagnostic and Statistical Manual of Mental Disorders (4th edn) (DSM-IV). Washington, DC: APA.
Ashton, C. H. (2001) Pharmacology and effects
of cannabis: a brief review. British Journal of
Psychiatry, 178,
101-106.
Brener, N. D., Collins, J. L., Warren, C. W., et al (1995) Reliability of the Youth Risk Behaviour Survey Questionnaire. American Journal of Epidemiology, 141, 575-580.[Abstract]
Chen, K. & Kandel, D. B. (1995) The natural history of drug use from adolescence to the mid-thirties in a general population sample. American Journal of Public Health, 85, 41-47.[Abstract]
Chen, K., Kandel, D. B. & Davies, M. (1997) Relationships between frequency and quantity of marijuana use and last year proxy dependence among adolescents and adults in the United States. Drug and Alcohol Dependency, 46, 53-67.[Medline]
Chilcoat, H. D. & Breslau, N. (1999) Pathways from ADHD to early drug use. Journal of the American Academy of Child and Adolescent Psychiatry, 38, 1347-1354.[Medline]
DeWit, D. J., Hance, J., Offord, D. R., et al (2000) The influence of early and frequent use of marijuana on the risk of desistance and of progression to marijuana-related harm. Preventive Medicine, 31, 455-464.[CrossRef][Medline]
Disney, E. R., Elkins, I. J., McGue, M., et al
(1999) Effects of ADHD, conduct disorder, and gender on
substance use and abuse in adolescence. American Journal of
Psychiatry, 156,
1515-1521.
Fergusson, D. M. & Horwood, L. J. (2000) Cannabis use and dependence in a New Zealand birth cohort. New Zealand Medical Journal, 113, 225-242.
Hall, W. & Degenhardt, L. (2000) Cannabis use and psychosis: a review of clinical and epidemiological evidence. Australian and New Zealand Journal of Psychiatry, 34, 26-34.[CrossRef][Medline]
Hall, W., Johnston, L. & Donnelly, N. (1999) Epidemiology of cannabis use and its consequences. In The Health Effects of Cannabis (eds H. Kalant, W. Corrigall, W. Hall, et al), pp. 71-125. Toronto: Centre for Addiction and Mental Health.
Johns, A. (2001) Psychiatric effects of
cannabis. British Journal of Psychiatry,
178,
116-122.
Johnston, L. D., O'Malley, P. M. & Bachman, J. G. (2000) Monitoring the Future: National Survey Results on Drug Use, 1975-1999. Bethesda, MD: National Institute on Drug Abuse.
Landgraf, J. M., Abetz, L. & Ware, J. E. (1996) The CHQ User's Manual. Boston, MA: The Health Institute, New England Medical Centre.
Lynskey, M.T. & Fergusson, D. M. (1995) Childhood conduct problems, attention deficit behaviors, and adolescent alcohol, tobacco, and illicit drug use. Journal of Abnormal Child Psychology, 23, 281-302.[Medline]
Lynskey, M.T., White, V., Hill, D., et al (1999) The prevalence of illicit drug use among youth: results from the Australian school students' alcohol and drugs survey. Australian and New Zealand Journal of Public Health, 23, 519-524.[Medline]
Perkonigg, A., Lieb, R., Hofler, M., et al (1999) Patterns of cannabis use, abuse and dependence over time: incidence, progression and stability in a sample of 1228 adolescents. Addiction, 94, 1663-1678.[CrossRef][Medline]
Radloff, L. S. (1977) The CESD scale: a self-report depression scale for research in the general population. Applied Psychological Measurement, 1, 385-401.
Reid, A., Lynskey, M. T. & Copeland, J. (2000) Cannabis use among Australian youth. Australian and New Zealand Journal of Public Health, 24, 596-602.[Medline]
Rey J. M., Sawyer, M. G., Clark, J. J., et al (2001) Depression among Australian adolescents. Medical Journal of Australia, 175, 19-23.[Medline]
Roberts, R. E., Lewinsohn, P. M. & Seely, J. R. (1991) Screening for adolescent depression: a comparison of depression scales. Journal of the American Academy of Child and Adolescent Psychiatry, 30, 58-66.[Medline]
Sawyer, M. G., Arney, F. M., Baghurst, P., et al (2000a) The Mental Health of Young People in Australia: Child and Adolescent Component of the National Survey of Mental Health and Wellbeing. Canberra: Australian Government Publishing Service.
Sawyer, M. G., Kosky, R. J., Graetz, B. W., et al (2000b) The National Survey of Mental Health and Wellbeing: the child and adolescent component. Australian and New Zealand Journal of Psychiatry, 34, 214-220.[CrossRef][Medline]
Schofield, W. N., Lovelace, K. S., McKenzie, J. E., et al (1998) Self reported tobacco and alcohol use among NSW secondary school students. In The 1996 Australian School Students Alcohol and Drugs Survey. Sydney: NSW Health Department and NSW Cancer Council.
Schubiner, H., Tzelepis, A., Milberger, S., et al (2000) Prevalence of attention-deficit/hyperactivity disorder and conduct disorder among substance abusers. Journal of Clinical Psychiatry, 61, 244-251.[Medline]
Shaffer, D., Fisher, P., Lucas, C. P., et al (2000) NIMH Diagnostic Interview Schedule for Children Version IV (NIMH DISC-IV): description, differences from previous versions, and reliability of some common diagnoses. Journal of the American Academy of Child and Adolescent Psychiatry, 39, 28-38.[Medline]
Smith, D. J. & Rutter, M. (1995) Time trends in psychosocial disorders of youth. In Psychosocial Disorders in Young People: Time trends and their causes (eds M. Rutter & D.J. Smith), pp. 763-781. New York: John Wiley & Sons.
Wilens, T. E., Biederman, J., Mick, E., et al (1997) Attention deficit hyperactivity disorder (ADHD) is associated with early onset substance use disorders. Journal of Nervous and Mental Disease, 185, 475-482.[CrossRef][Medline]
Received for publication April 24, 2001. Revision received September 17, 2001. Accepted for publication September 27, 2001.
Related articles in BJP: