No definite link between cannabis use and suicide: our review

We’ve published an interesting review (aren’t they all though?) on a study that discussed the lack of association between marijuana and suicide risk, in what our reviewer Wayne Hall from the University of Queensland, Australia, described as “the largest and best controlled prospective study of the relationship to date“.

It’s a tough topic to tackle, especially in a time when celebrity deaths, marijuana usage and suicide are so closely linked by tabloid media (Marilyn Monroe being the newest revelation) and when fears that teenage brains getting destroyed by cannabis are high on the news agenda. But on the other hand, when a highly-respected scientist such as Professor David Nutt gets vilified by the government for his outspoken views on drugs policy, the media generally showed support for the sacked Professor while still being skeptical of his evidence-based comments (such as cannabis use being safer than horse riding).

Hall looked at the paper, Cannabis and suicide: longitudinal study, by Allebeck and Price at al. from Cardiff University UK, published in the British Journal of Psychiatry, which went beyond previous small cross-sectional studies to look at whether the cannabis/suicide attempt relationship took into account pre-existing suicide risk between young people who become regular cannabis users and their peers who do not.

In the study, more than 50,000 Swedish men aged 18-20 were followed up for 33 years using death registers to identify those who had died from suicide.

Hall says:

As in previous studies, self-reported cannabis use at conscription was positively related to suicide (odds ratio [OR]=1.62, 95% confidence interval [CI] 0.65-2.07) but this association was no longer significant when plausible potential confounders, such as problematic behavior during childhood, intelligence, alcohol abuse, parental psychiatric disorder, other drug use, and psychiatric diagnosis at conscription were statistically controlled for by logistic regression (OR=0.88, 95% CI 0.65-1.20). The selection of confounders to control for did not affect the finding that the OR was no longer significant after adjustment for confounders. This study strongly suggests that the modest association observed between regular cannabis use and suicide in cross sectional studies reflects the fact that young people who are at marginally higher risk of suicide are more likely to become regular cannabis users than their peers.

And it’s the last point that is most pressing: those at a slightly higher suicide risk are more likely to become regular pot smokers, not the other way round. If you look at the citation rates on Google Scholar for “cannabis and suicide”, many academics seem to support the view that the two are  strongly linked.

Allebeck and Price’s earlier paper, published in 1990 at this study’s 15-year mark, even stated “the proportion of suicides increased sharply with the levelof cannabis consumption“: their new study clarified that the “association was eliminated after adjustment for confounding” and the link was better explained by markers of psychological and behavioural problems.

No doubt long-term studies such as this will lend more weight to the Nutt debate and, if they are given adequate publicity, hopefully help to cut down on biased anti-drug journalism.

[Via http://blog.f1000.com]