In a longitudinal cohort of people with bipolar disorder, increases in cannabis use frequency predicted higher suicidal ideation at subsequent timepoints.
psychiatrists treating bipolar disorder, suicide prevention researchers, substance use clinicians
What the researchers found
When a person had more frequent and intense cannabis use compared to their average, they had higher suicidal ideation at the next timepoint. Alcohol and substance use impairment also predicted future suicidal ideation. Cocaine frequency/intensity and substance use impairment were concurrently associated with suicidal ideation.
Why it matters
Suicidal ideation is a major concern in bipolar disorder. This study provides prospective evidence that within-person increases in cannabis use precede worsening suicidal thoughts, which has implications for monitoring and clinical guidance.
The numbers in context
788 participants with BSD. Median enrollment: 72 months. BD I: n=565, BD II: n=162, BD NOS: n=61. Cannabis use intensity/frequency predicted next-timepoint SI. Alcohol/substance impairment predicted next-timepoint SI. Cocaine I/F concurrently associated with SI.
How the study worked
Longitudinal cohort of 788 participants with bipolar I (n=565), bipolar II (n=162), and BD NOS (n=61) with median enrollment of 72 months. Alcohol and substance use measured via modified AUDIT every 6 months. Suicidal ideation measured via PHQ-9 item 9 every 2 months. Dynamic structural equation models tested prospective associations.
What this study cannot tell us
Observational design cannot establish causation. Cannabis use measured every 6 months while SI measured every 2 months, creating temporal resolution mismatch. Self-reported substance use. Potential for reverse causation (increased SI driving cannabis use).
How to read the evidence
Large longitudinal cohort with within-person analysis and sophisticated modeling, though measurement timing mismatch and observational design limit to moderate.
When this study was published
Data from a long-term bipolar disorder cohort study.
The bigger picture
The within-person design is important because it shows that when the same individual uses more cannabis than usual, their suicidal thinking increases. This is stronger evidence than cross-sectional comparisons between people, though still cannot prove causation.
Questions still open
- Does cannabis use cause increased SI, or does worsening mood drive both cannabis use and SI?
- Would monitoring cannabis use changes improve suicide risk assessment in bipolar disorder?
Common questions
Does cannabis make suicidal thoughts worse in bipolar disorder?
Is cannabis uniquely risky for bipolar disorder?
Read the original research
Alcohol and substance use differentially impact suicidal ideation in a longitudinal cohort of bipolar disorder.
Psychiatry research, 344, 116357
Citation
Smith, Julia L; McInnis, Melvin G; Sperry, Sarah H. (2025). Alcohol and substance use differentially impact suicidal ideation in a longitudinal cohort of bipolar disorder.. Psychiatry research, 344, 116357. https://doi.org/10.1016/j.psychres.2025.116357
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