Secondary analysis of the relationship between cannabis use, dependence mental health and associated outcomes in the Victorian Adolescent Cohort study

NDARC Staff

Wendy Swift, Louisa Degenhardt, Bianca Calabria and Delyse Hutchinson

Other Investigators

George Patton and Carolyn Coffey (Centre for Adolescent Health, The Royal Children's Hospital, Melbourne); John Carlin (Murdoch Children’s Research Institute); Wayne Hall (School of Population Health, University of Queensland); and Steve Allsop (National Drug Research Institute, Curtin University of Technology)

Rationale

There is much current concern and publicity about the relationship between cannabis use and dependence, mental health, other drug use and related psychosocial outcomes, particularly among young people. While there is a growing body of evidence suggesting a relationship, the nature of the relationship is complex and there are many methodological issues involved. Longitudinal research provides a sound methodology for investigating these issues, and large, well-controlled cohort studies are increasingly contributing to the evidence base. While much published longitudinal research emanates from overseas, there are excellent Australian birth and adolescent cohorts that have collected a wealth of data which can also address the longitudinal psychosocial impact of cannabis use among young people.

Aims

This project involved a collaboration with the Victorian Adolescent Cohort Study (VACS), which commenced in 1992. It aimed to conduct secondary analyses and produce peer-reviewed papers on four related areas around the long-term impacts of cannabis use in adolescence and young adulthood: the relationship between cannabis and other drug use, the natural history of cannabis use (patterns of use, abuse and dependence), cannabis use and mental health (especially depression and anxiety) and cannabis use and life transitions.

Design and Method

The VACS has collected eight waves of data from a representative sample of Victorian adolescent school children, who are now in their late twenties. One class from each school entered the cohort in the latter part of the ninth school year (wave 1) and the second class six months later, early in the tenth school year (wave 2). Participants were subsequently reviewed at four six-month intervals during the teens (waves 3 to 6) with two follow-up waves in young adulthood aged 20-21 years (wave 7) and 24-25 years (wave 8). The first six surveys alone created one of the most comprehensive pictures of adolescent development available. This information has been used to improve the health of future generations by influencing policy and informing prevention programs. The eighth survey was completed in 2001-2003. At this time, 1520 participants were surveyed (76% retention). This cohort study has collected comprehensive information on a range of issues, including: mental health, drug use, personality, relationships, and physical and sexual health.
Secondary analyses were conducted using data from the eight waves of the cohort. Wave 9 data, which became available during the project, were included in some relevant analyses. The following areas were examined:(i) the relationship between cannabis and other drug use; (ii) the natural history of cannabis use; (iii) cannabis use and mental health; and (iv) cannabis use and life transitions.

Benefits

The Victorian Adolescent Cohort Study is one of the most comprehensive pictures of adolescent development available, influencing policy and informing prevention programs. This study builds on this study to investigate the relationships between cannabis use, mental health, and related issues. There is still much uncertainty and ongoing debate over these relationships. Longitudinal research provides a sound methodology for investigating these issues, and this presents a real opportunity to understand these important relationships in an Australian context.

Output

Three papers from this study have been published (references below), one is currently under review and two papers are in draft.

Swift, W., Coffey, C., Carlin, J.B., Degenhardt, L. & Patton, G. (2009) Are adolescents who moderate their cannabis use at lower risk of later problematic cannabis use? Addiction 104, 806-814.

Swift, W., Coffey, C., Carlin, J.B., Degenhardt, L. & Patton, G. (2008). Adolescent cannabis users at 24 years: trajectories of ongoing and problematic use. Addiction 103, 1361-1370.

Degenhardt, L., Coffey, C., Carlin, J.B., Swift, W. & Patton, G.C. (2008). Are diagnostic orphans at risk of developing cannabis abuse or dependence? Four year follow up of young adult cannabis users not meeting diagnostic criteria. Drug and Alcohol Dependence 92, 86-90.

Three presntations have been made at national and international conferences:

Swift, W., Coffey, C., Carlin, J.B., Degenhardt, L. & Patton, G.C. (2008, June). Adolescent cannabis users at age 24: trajectories of ongoing problematic use. Poster presented to the 70^th Annual Meeting of the College of Problems on Drug Dependence, San Juan, Puerto Rico.

Swift, W., Coffey, C., Carlin, J.B., Degenhardt, L. & Patton, G.C. (2008, November). Trajectories of adolescent cannabis use to problematic use in young adulthood. Paper presented to the Annual APSAD Conference, Sydney.

Swift, W. (2008, August). Secondary analyses of cannabis use in the Victorian Adolescent Cohort Study. Paper presented at the NDARC Annual Symposium, Sydney.

Funding

Australian Government Department of Health and Ageing