What topics does this cannabis study cover?

This study covers research on: Mental Health, Addiction.

Cannabis use predicted suicidal behaviour despite regional differences

Q: What did this research study find?

In this *longitudinal observational study* of **1,470 young adults**, higher cannabis use at age 25 and increased consumption at age 29 predicted **increased suicidal behaviour**.

Q: Where was this research published?

Published in Prevention science : the official journal of the Society for Prevention Research on September 24, 2026.

Longitudinal Effects of Cannabis Use on Suicidal Behaviour in Early Adulthood in Washington State, United States and Victoria, Australia.

Prevention science : the official journal of the Society for Prevention Research • September 24, 2026 • Highly Relevant

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AI Summary

This observational longitudinal study examined whether cannabis use was associated with suicidal behaviour in 1,470 young adults from Washington State, United States, and Victoria, Australia. The matched cohorts were surveyed at average ages 25 and 29, allowing researchers to compare a region where recreational cannabis was legalised in 2012 with one where it remained illegal. Washington participants reported higher past-year cannabis use at age 25, and their cannabis use increased through their late 20s, while use declined among Victorian participants.

The analyses found that higher cannabis use at age 25 and increased consumption at age 29 predicted more suicidal behaviour, and earlier suicidal behaviour also predicted later suicidal behaviour. Propensity analyses supported associations between cannabis use and suicidal behaviour, as well as between legalisation-related measures and cannabis use. However, Washington had lower self-harm at age 29 despite higher cannabis use, highlighting that multiple factors likely shape regional differences. Because this was an observational study based on self-reports and regional comparisons, the abstract cannot establish that cannabis caused suicidal behaviour or determine which other factors explain the differences between locations. This is an abstract-based summary, not a full-text review.

💡 Key Findings

In this longitudinal observational study of 1,470 young adults, higher cannabis use at age 25 and increased consumption at age 29 predicted increased suicidal behaviour.

Good

75%

Washington State participants reported higher cannabis use than Victorian participants, with use increasing in Washington and declining in Victoria from ages 25 to 29.

High

80%

Earlier suicidal behaviour predicted later suicidal behaviour, with the predictive risk reported as higher in Washington State.

Good

75%

Despite greater cannabis use, Washington State had lower self-harm at age 29 than Victoria, indicating that regional differences in suicidal behaviour involve more than cannabis availability or use alone.

High

80%

The study found associations between cannabis use and suicidal behaviour, but its observational design cannot establish causation.

High

95%

📄 Original Abstract

This study aimed to investigate the impact of cannabis use on young adult suicidal behaviour. Matched cohorts were compared across two regions: Washington State, USA (where recreational cannabis use was legalised in 2012) and Victoria, Australia (where recreational cannabis use remains illegal). The hypotheses were (1) cannabis use would be more prevalent in Washington State in association with legalisation and (2) cannabis use would predict suicidal behaviour similarly in both regions. Data were drawn from the International Youth Development Study (IYDS) involving 1,470 participants (55.4% female; 726 Victoria, 744 Washington State) surveyed at average ages 25 and 29 in 2014 and 2018, respectively. Participants completed self-report surveys assessing demographic data, cannabis use, other forms of substance use, proximity to cannabis sales outlets, and suicidal behaviour. Data were analysed using multivariate negative binomial regression to identify cannabis use predictors of incident suicidal behaviour and differences between the two regions. Washington State participants reported significantly higher past-year cannabis use compared to Victorian participants at age 25 (in 2014) and lower self-harm at age 29 (2018). Victorian participants reported a reduction in cannabis use from age 25 to 29, while increased use was reported by Washington State participants across the same period. Regression analysis showed higher rates of cannabis use at 25 years and increased cannabis consumption at 29 years predicted increased suicidal behaviour. Suicidal behaviour in 2014 predicted this behaviour in 2018, with higher predictive risk in Washington State. Propensity score analysis confirmed a significant effect of cannabis use on suicidal behaviour. The effect of legalisation indicators (Washington State location, proximity to cannabis stores) on cannabis use was also significant based on propensity analysis. Cannabis was more prevalent in Washington State through the late 20 s. Young adult cannabis use increased the likelihood of suicidal behaviours. Despite increased risk from cannabis use, Washington State maintained lower rates of suicidal behaviour compared to Victoria, emphasising the need to understand multiple determinants of state differences in suicidal behaviour.

Paper Type

📄 Research

Publication

Journal: Prevention science : the official journal of the Society for Prevention Research
Published: September 24, 2026
PMID: 42782471
DOI: 10.1007/s11121-026-01987-z

Authors (5)

Abbey J Fitzpatrick Centre for Social and Early Emotional Development, School of Psychology, Deakin University, 221 Burwood Highway, Burwood, VIC, 3125, Australia. abbeyjfitz26@gmail.com.
Jessica A Heerde Centre for Social and Early Emotional Development, School of Psychology, Deakin University, 221 Burwood Highway, Burwood, VIC, 3125, Australia.
Bosco Rowland Monash Addiction Research Centre (MARC), 110 Church Street, Richmond, VIC, 3121, Australia.
Ebru A Batmaz Centre for Social and Early Emotional Development, School of Psychology, Deakin University, 221 Burwood Highway, Burwood, VIC, 3125, Australia.
John W Toumbourou Centre for Social and Early Emotional Development, School of Psychology, Deakin University, 221 Burwood Highway, Burwood, VIC, 3125, Australia.