Joseph Boden writes:
In 101 days, New Zealanders will determine whether or not cannabis should be legalised. In making that decision, there is plenty to learn from the Christchurch and Dunedin longitudinal studies, which together have contributed a vast amount of knowledge regarding cannabis-related harm.
The Christchurch Health and Development Study and the Dunedin Multidisciplinary Health and Development Study were both founded in the 1970s. Each includes more than 1000 participants, with individuals followed into their 40s. Along the way we have repeatedly asked about their involvement with cannabis and problems arising from this. Professor Wayne Hall of the University of Queensland, an internationally renowned figure in substance use research, has referred to our studies in the context of cannabis research as “the best designed and most informative of these [epidemiological] studies”.
These studies are the gold standard for research.
What did we find? We learned that cannabis use is very common, with as many as 80% of participants having used cannabis on at least one occasion. Rates of regular use (using at least weekly) were far lower (35%). We also found that higher levels of cannabis use, particularly at younger ages, were related to mental health problems including increased risk of cannabis use disorder and major depression. Most strikingly, earlier and heavier cannabis use was also related to increased reports of psychotic symptoms in…
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