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Cannabis-Related Self-Harm & Emergency Room Visits (2010-2021): Increasing Since Legalization

The legalization and liberalization of cannabis in Canada have sparked debates and concerns regarding its impact on public health, particularly in the context of self-harm behaviors.

A comprehensive study in Ontario, Canada, spanning from 2010 to 2021, has revealed significant findings on the relationship between cannabis use and emergency department (ED) visits for self-harm.


  1. Of the 158,912 self-harm ED visits in Ontario, Canada, between 2010 and 2021, 4.9% involved cannabis, marking a significant increase in cannabis-related self-harm incidents over the years.
  2. The annual rate of self-harm ED visits involving cannabis surged by 90.1% from 2010 to 2021, indicating a growing public health concern.
  3. The liberalization of medical cannabis was associated with the observed increase in self-harm incidents involving cannabis, highlighting the potential impact of cannabis policy changes on self-harm behaviors.
  4. Despite the increase in cannabis-related self-harm, alcohol-involved self-harm incidents saw a 17.3% decline, suggesting shifting patterns in substance use related to self-harm.

Source: Journal of Affective Disorders (2024)

How Cannabis May Increase Risk of Self-Harm ER Visits

The relationship between cannabis use and self-harm emergency department (ED) visits is complex, influenced by various mechanisms.

1. Psychological Effects

Mental Health Disorders: Cannabis use has been associated with an increased risk of developing mental health disorders such as depression, anxiety, and psychosis. Individuals with these conditions may be more prone to self-harm behaviors, leading to an increase in ED visits.

Impaired Judgment: THC, the psychoactive component of cannabis, can impair judgment and increase impulsivity. This impairment may lead to risky behaviors, including self-harm, particularly in individuals with pre-existing mental health issues or those under significant stress.

2. Substance Use Disorders

Dependence & Withdrawal: Regular and heavy cannabis use can lead to dependence. The withdrawal process can be psychologically challenging, contributing to distress, anxiety, and depressive symptoms, which may increase the likelihood of self-harm.

Polysubstance Use: Cannabis users may also use other substances, such as alcohol or opioids, which can exacerbate mental health issues and increase the risk of self-harm. The interaction between substances can lead to a higher risk of engaging in self-harm behaviors.

3. Social & Behavioral Factors

Social Isolation: Individuals who use cannabis heavily may experience social isolation due to stigma, legal issues, or lifestyle choices centered around substance use. Social isolation is a significant risk factor for depression and self-harm.

Coping Mechanism: Some individuals may use cannabis as a coping mechanism for dealing with emotional pain or traumatic experiences. When cannabis is no longer sufficient to manage these feelings, they may resort to self-harm as an alternative coping strategy.

4. Cannabis-Induced Conditions

Cannabis-induced Psychosis: In rare cases, cannabis use can lead to acute psychosis, characterized by hallucinations, delusions, and a loss of touch with reality. Individuals experiencing cannabis-induced psychosis may engage in self-harm due to delusional beliefs or as a response to hallucinations.

Cannabinoid Hyperemesis Syndrome (CHS): CHS is a condition that can occur with chronic cannabis use, characterized by severe cyclic vomiting. The distress and discomfort associated with CHS may lead to desperation and self-harm in affected individuals seeking relief.

5. Brain Development

In adolescents and young adults, cannabis use can affect the developing brain, potentially altering areas involved in impulse control and emotional regulation.

These changes may increase the propensity for self-harm behaviors among young users.

Cannabis & ER Visits for Self-Harm in Ontario Over 11-Year Period: Major Findings (2024)

1. Rates of Cannabis Involvement in Self-Harm ED Visits

Finding: Among the 158,912 self-harm ED visits recorded between 2010 and 2021, 4.9% involved cannabis.

Explanation: This indicates a substantial presence of cannabis use among individuals engaging in self-harm behaviors, necessitating a closer look at the role of cannabis in such incidents. The finding underscores the need for healthcare providers to be vigilant about substance use, particularly cannabis, when assessing patients presenting with self-harm.

2. Significant Increase in Cannabis-Involved Self-Harm Incidents

Finding: The study observed a 90.1% increase in the annual rate of cannabis-involved self-harm ED visits per 100,000 individuals, climbing from 3.6 in 2010 to 6.9 in 2021.

Explanation: This dramatic rise highlights a growing public health concern tied to increased cannabis use or its greater detection in the context of self-harm incidents. The finding suggests that the liberalization and legalization of cannabis may have contributed to increased accessibility and use, potentially influencing self-harm behaviors.

3. Decrease in Alcohol-Involved Self-Harm Incidents

Finding: While cannabis-involved incidents surged, self-harm incidents involving alcohol decreased by 17.3% over the study period.

Explanation: This contrasting trend between cannabis and alcohol involvement in self-harm incidents might indicate shifting patterns of substance use. It raises questions about the substitution effect, where individuals might be turning to cannabis over alcohol, and its implications for self-harm behaviors.

4. Impact of Cannabis Policy Changes

Finding: The increase in cannabis-related self-harm incidents was notably observed after the liberalization of medical cannabis, with no further significant increases during later policy periods.

Explanation: This temporal association suggests that the initial phase of cannabis policy liberalization, which increased access to and perhaps normalized cannabis use, may have been a critical factor contributing to the rise in self-harm incidents involving cannabis. It indicates that policy changes can have profound, albeit complex, impacts on public health outcomes.

5. Demographic Variations

Additional Analysis: The study also revealed that increases in cannabis-involved self-harm incidents were more pronounced among adults and women.

Explanation: These demographic insights are crucial for tailoring prevention and intervention strategies. The greater vulnerability of certain groups underscores the importance of targeted public health messaging and supports to address the specific risks and needs related to cannabis use and self-harm behaviors.

Cannabis & Emergency Room Visits for Self-Harm (2010-2021 in Ontario)

Daniel T Myran et al. evaluated ER visits in Ontario between 2010-2021 related to self-harm and cannabis.

Researchers examined the link between the liberalization of medical cannabis, the legalization of non-medical cannabis, and changes in self-harm behaviors, as observed in ED visits.

They also compared trends in cannabis-involved self-harm incidents with those involving alcohol, using the latter as a control to account for overall trends in substance use and self-harm behaviors.


  • Data: Employing a repeated cross-sectional approach, the study utilized health administrative data to track all ED visits for self-harm among individuals aged ten and older. It specifically identified incidents of self-harm with a co-diagnosis of cannabis use, comparing these to incidents involving alcohol use.
  • Analysis: The study was segmented into four distinct cannabis policy periods, allowing for a detailed examination of trends over time.
  • Tools: Advanced statistical methods, including Poisson models and segmented regression analysis, were applied to discern changes in the rates of self-harm incidents involving cannabis and alcohol across the defined policy phases.


  • Incidence Rate: The study encompassed 158,912 individuals, with findings indicating that 4.9% of self-harm ED visits involved cannabis. Notably, there was a 90.1% increase in the annual rate of cannabis-involved self-harm ED visits per 100,000 individuals, escalating from 3.6 in 2010 to 6.9 in 2021.
  • Comparison with Alcohol: In contrast to cannabis, self-harm incidents involving alcohol saw a decrease of 17.3% during the study period.
  • Policy Impact: A pivotal observation was that the surge in cannabis-related self-harm incidents predominantly occurred post the medical cannabis liberalization, with no significant upticks during subsequent policy periods.


  • Documentation: The observed increase in cannabis involvement might be partially attributed to enhanced awareness and documentation practices among healthcare providers.
  • Causality: While the study establishes a correlation between cannabis involvement and self-harm incidents, it does not prove causality.
  • Competing Events: External factors, such as the 2018 decline in overall self-harm ED visits and the COVID-19 pandemic’s impact, complicate attributions of changes to cannabis policy liberalization alone.
  • Data Completeness: The potential underestimation of cannabis-involved self-harm incidents due to data limitations suggests the actual figures might be higher.

What are some potential applications of the findings?

  1. Public Health: The study’s findings can inform targeted public health interventions aimed at reducing self-harm behaviors, especially among cannabis users. By recognizing the increased prevalence of cannabis involvement in self-harm incidents, healthcare providers and policymakers can develop specific strategies, such as awareness campaigns and educational programs, to address the risks associated with cannabis use.
  2. Policy Development: The temporal association between cannabis policy liberalization and an increase in self-harm incidents underscores the need for careful consideration of public health impacts in cannabis legislation. Policymakers could use these insights to craft more nuanced cannabis laws and regulations that balance access with preventive measures against potential harms, including targeted restrictions or guidelines for medical cannabis.
  3. Healthcare Training: Enhanced training for healthcare providers on the implications of cannabis use for mental health and self-harm risk is another crucial application. This training can improve the detection and management of cannabis use in patients presenting with self-harm, enabling timely and appropriate interventions.
  4. Substance Use Treatment: The findings highlight the necessity for integrating substance use discussions, particularly concerning cannabis, into treatment programs for individuals at risk of self-harm. Tailoring treatment approaches to address the specific challenges and risks posed by cannabis use can improve patient outcomes.
  5. Research: The study opens new avenues for research into the mechanisms linking cannabis use to self-harm and the long-term effects of cannabis policy changes on public health. Further studies could explore demographic-specific impacts, the role of cannabis potency, and the effectiveness of different intervention strategies.

Takeaway: Cannabis Use, Legalization, Self-Harm

The comprehensive study from Ontario, Canada, sheds critical light on the complex relationship between cannabis use, policy liberalization, and self-harm behaviors.

By documenting a significant increase in cannabis-involved self-harm incidents following the liberalization of medical cannabis, the study underscores the unintended consequences of policy changes on public health.

The decrease in alcohol-involved self-harm incidents further highlights shifting patterns of substance use, pointing to the need for adaptive public health strategies.

These findings offer a valuable foundation for developing targeted interventions, informing policy reform, and guiding future research.

As cannabis legalization continues to evolve globally, the insights from this study are crucial for mitigating the potential public health impacts, ensuring that policy advancements are informed by a nuanced understanding of their implications for substance use and self-harm behaviors.


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