The publication last week of a substantial meta-analysis of the link between cannabis and psychosis has brought about some significant debate both in the maintsream media and the AOD profession.
The Lancet podcast interviews one of the article’s authors and he’s very up front about the fact that establishing causality from a meta-analysis is fraught with difficulty. That said, the paper’s authors believe around 50% of cannabis-related psychosis is probably related to other factors like use of other substances, pre-existing mental illness and so on. That still leaves 50% of cases where there may be a direct causal link. The authors go to great lengths to emphasise that the link cold be explained by another factor, but that given there’s not likely to be significant new findings in the near future, the current practice of advising that cannabis use canbring a risk of psychosis is an appropriate strategy.
Dr Malcolm Dobbs from the Victorian Department of Health and Human Services summarised the issue perfectly:
“We don’t have perfect evidence about whether there is a causal relationship between cannabis use and increased risk of psychosis, but this meta-analysis has confined its choice of studies to longitudinal cohorts, and made allowances for possible factors that could explain (confound) differences in risks between cannabis users and non-users.
The authors of the comment estimate that if there is a true causal relation, the increased risk would mean that 800 yearly cases of schizophrenia in the UK could be prevented through cessation of cannabis consumption.”
Of course, whether a direct causal link is established or not, the pivotal issue is effective education programs and not falling into the trap of demonising a substance that has some demonstrably beneficial medical effects in the right circumstance. Any illicit substance is great fodder for misrepresentative sensationalism. The meta-analysis is purely another small step toward understanding the link between cannabis and mental health – there’s still plenty of work to be done yet.