Aims: To determine change in patterns of cannabis use in New Zealand in an unselected birth cohort and investigate the relationship between level of cannabis use, violent behaviour and employment history.
Method: Prospective longitudinal design using members of the Dunedin Multidisciplinary Health and Development Study at ages 15, 18 and 21 years.
Results: Rates of cannabis use increased from 15% (n = 144) at age 15 years to more than half of the sample seen at age 21 years (n = 497; 52.4%). DSM-III-R defined cannabis dependence assessed at age 18 and 21 years increased from 6.6% (n = 61) to 9.6% (n = 91). Males were more likely to use and be dependent on cannabis than females. Early use substantially increased the risk for the development of cannabis dependence in young adulthood. Cross-sectional analysis at age 21 found levels of cannabis use and dependence to be higher among the unemployed and those with a history of violent behaviour.
Conclusions: Prevalence rates of cannabis use in young New Zealanders were found to be higher than previously reported. A history of unemployment or of violent behaviour was associated with more frequent cannabis use at age 21. Males were more likely than females to use cannabis frequently and to meet DSM-III-R criteria for dependence at age 21. It is suggested that drug education campaigns should specifically target young males.