Cannabis Was Not an Independent Suicide Risk Factor in Psychosis After Accounting for Depression | Research

The takeaway

Among 1,790 Australians with psychotic disorders, daily cannabis use was initially linked to higher suicide attempt rates, but this association disappeared after controlling for depression, loneliness, homelessness, and hallucinations.

Psychiatrists, suicide prevention researchers, psychosis treatment providers.

Depression was the strongest predictor of suicide attempts for both sexes; the cannabis association disappeared after controlling for depression and social factors.

What the researchers found

In unadjusted analyses, daily cannabis users of both sexes had significantly increased odds of suicide attempts. After adjusting for depression, loneliness, homelessness, and hallucinations, the association was no longer significant. Depression was the strongest predictor for both sexes. Post hoc analysis found daily cannabis use may increase risk in older men specifically.

Why it matters

While cannabis is often assumed to increase suicide risk in psychosis, this study shows the apparent association is largely explained by depression and social adversity. This redirects clinical attention to treating depression and addressing social factors rather than focusing solely on cannabis use.

The numbers in context

1,790 participants total. 168 (9.4%) attempted suicide in the past year. Daily cannabis users had elevated risk in unadjusted analysis, but not after adjustment. Depression was the strongest predictor for both sexes.

How the study worked

Analysis of data from 1,065 men and 725 women in the Australian national survey of psychosis. Separate models for each sex examined the impact of daily, casual, or no past-year cannabis use on past-year suicide attempts.

What this study cannot tell us

Cross-sectional design cannot determine causation. Self-reported cannabis use and suicide attempts. Cannot fully separate the effects of cannabis from its correlates. Post hoc subgroup finding (older men) needs replication.

How to read the evidence

Moderate - large national survey with sex-stratified analysis and appropriate confounding adjustment.

When this study was published

Published in 2018.

The bigger picture

The relationship between cannabis, psychosis, and suicide is more nuanced than often presented. Cannabis users with psychosis may be at higher suicide risk because of associated factors (depression, social isolation) rather than cannabis use itself.

Questions still open

Does cannabis contribute to the development of depression and social isolation in psychosis patients, creating an indirect pathway to suicide? Why might older men be specifically vulnerable? Would treating depression reduce the cannabis-suicide association entirely?

Common questions

Does cannabis increase suicide risk in people with psychosis?

Not directly, according to this study. While daily cannabis users initially appeared at higher risk, this association was fully explained by depression, loneliness, homelessness, and hallucinations. These co-occurring factors, rather than cannabis itself, appear to drive the elevated risk.

What is the biggest suicide risk factor in psychosis?

Depression was the strongest predictor of suicide attempts for both men and women with psychotic disorders in this study of 1,790 Australians. Social factors like loneliness and homelessness were also significant contributors.

Read the original research

Is cannabis a risk factor for suicide attempts in men and women with psychotic illness?

Psychopharmacology, 235(8), 2275-2285

View on PubMed ↗Publisher’s paper ↗

Citation

Waterreus, A; Di Prinzio, P; Badcock, J C; Martin-Iverson, M; Jablensky, A; Morgan, V A. (2018). Is cannabis a risk factor for suicide attempts in men and women with psychotic illness?. Psychopharmacology, 235(8), 2275-2285. https://doi.org/10.1007/s00213-018-4924-6