Cannabis-related hospital visits were followed by a 5-fold increase in self-harm and 9-fold increase in suicide risk | Research

The takeaway

In an Ontario population study of over 11 million people, those with cannabis-related hospital contacts had a 5.4-fold increased risk of deliberate self-harm and 9.2-fold increased risk of suicide death within 3 years.

Emergency medicine physicians, psychiatrists, suicide prevention researchers, and mental health policy makers.

9.2x increased risk of suicide death within 3 years of cannabis-related hospital contact

What the researchers found

Cannabis-related hospital contact was associated with a 5.35x risk of deliberate self-harm and 9.22x risk of death by suicide compared to the general population. Even after excluding those with co-morbid mental health or substance use disorders, self-harm risk remained elevated at 7.18x.

Why it matters

This is one of the largest population studies linking cannabis-related hospital contacts to subsequent self-harm and suicide. The finding that risk persists even without pre-existing mental health conditions suggests cannabis-related hospital visits should trigger mental health screening.

The numbers in context

11,320,897 followed. 85,108 (0.75%) had cannabis-related hospital contacts. Self-harm aHR: 5.35. Suicide death aHR: 9.22. Without mental health comorbidity: self-harm aHR: 7.18. Median follow-up: 5 years.

How the study worked

Population-level retrospective study of 11,320,897 people in Ontario, Canada. 85,108 with incident cannabis-related ED visits or hospitalizations were matched with general population controls. Adjusted hazard models controlled for sociodemographics, mental health comorbidities, chronic conditions, and substance use.

What this study cannot tell us

Hospital contacts capture severe or problematic use, not typical cannabis use. Residual confounding from unmeasured factors is likely. Cannot determine causation.

How to read the evidence

Massive population-level study with comprehensive matching and sensitivity analyses. However, hospital contacts represent the severe end of cannabis use.

When this study was published

Published in 2025.

The bigger picture

As cannabis use disorder prevalence grows globally, these findings have implications for emergency department protocols. Identifying cannabis-related visits as a potential marker for suicide risk could enable preventive interventions.

Questions still open

Would routine mental health screening after cannabis-related ED visits reduce subsequent self-harm? Is the association causal or does it reflect shared vulnerability?

Common questions

Does cannabis use increase suicide risk?

This study found that people who had cannabis-related hospital visits had a 9.2x higher risk of dying by suicide. However, these visits represent severe or problematic use, not typical cannabis consumption.

Was the risk only in people with existing mental health conditions?

No. Even after excluding people with diagnosed mental health or substance use disorders, the self-harm risk remained 7.2x higher.

Read the original research

Deliberate self-harm and suicide in individuals with cannabis-related hospital contacts in Ontario, Canada.

Molecular psychiatry

View on PubMed ↗Publisher’s paper ↗

Citation

Fabiano, Nicholas; Vargatoth, Emi; Pugliese, Michael; MacDonald-Spracklin, Rachael; Willows, Melanie; Solmi, Marco; Myran, Daniel T. (2025). Deliberate self-harm and suicide in individuals with cannabis-related hospital contacts in Ontario, Canada.. Molecular psychiatry. https://doi.org/10.1038/s41380-025-03339-9