Frequent cannabis use linked to suicidal thoughts in males over 30-year follow-up

What the researchers found

Using data from a 30-year birth cohort study, researchers examined the directional relationship between cannabis use and suicidal ideation. They found that intensive cannabis use, defined as several times per week or more, was associated with a higher rate of transitioning into suicidal ideation among males.

Importantly, the analysis tested the reverse direction as well: whether suicidal ideation led to cannabis use. No evidence supported this pathway for either males or females. The one-directional nature of the finding strengthens the case for a meaningful link between heavy cannabis use and suicidal thinking in males, though the study did not establish direct causation.

Why it matters

Suicide is the second leading cause of death among youth aged 10 to 24 globally. Understanding modifiable risk factors is critical. The directional finding that heavy cannabis use preceded suicidal ideation, rather than the reverse, contributes important evidence to the public health picture.

The numbers in context

The study followed a birth cohort for 30 years. Intensive cannabis use (several times per week or more) was associated with increased suicidal ideation in males. No reverse-direction effect was found for either sex.

How the study worked

This was a longitudinal analysis based on the Christchurch Health and Development Study, a 30-year follow-up of a birth cohort in New Zealand. Researchers used hazard rate models to examine both whether cannabis use predicted transitions into suicidal ideation and whether suicidal ideation predicted transitions into cannabis use.

What this study cannot tell us

The association was observed only in males, limiting generalizability. Even with longitudinal data and directional modeling, uncontrolled confounders could explain the relationship. The study defined "intensive" use broadly and did not assess cannabis potency or specific cannabinoid exposure.

How to read the evidence

Thirty-year birth cohort study with directional analysis. Strong longitudinal design from a well-established cohort.

When this study was published

Published in 2013, based on data from the Christchurch Health and Development Study beginning in 1977.

The bigger picture

This study is part of a growing body of evidence linking heavy cannabis use to mental health outcomes. The directional analysis adds strength beyond simple cross-sectional associations by showing that cannabis use preceded the outcome rather than following from it.

Questions still open

• Why was the association observed only in males? Does cannabis potency or THC content modify this risk? What biological or psychological mechanisms might link heavy cannabis use to suicidal thinking?

Common questions

Read the original research

Cannabis use and suicidal ideation.

Journal of health economics, 32(3), 524-37

Citation

van Ours, Jan C; Williams, Jenny; Fergusson, David; Horwood, L John. (2013). Cannabis use and suicidal ideation.. Journal of health economics, 32(3), 524-37. https://doi.org/10.1016/j.jhealeco.2013.02.002

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