The relationship between cannabis use and schizophrenia has been a topic of medical and public health concern for years. With cannabis legalisation gaining momentum across the globe, including Canada, new questions arise about the unintended consequences such policies may bring. One particular concern is whether legalisation leads to an increase in cases of cannabis use disorder (CUD) and the subsequent rise in schizophrenia diagnoses.

This article dives into recent research focused on Canada, exploring how cannabis use and schizophrenia are interconnected and what those findings mean for public health and policy.

Understanding Cannabis Use Disorder and Schizophrenia

Cannabis use disorder (CUD) is characterised by a pattern of cannabis use leading to clinically significant impairment or distress. People with CUD often experience difficulty controlling their cannabis consumption, even when it leads to social, psychological, or health problems.

Schizophrenia, on the other hand, is a severe mental health condition marked by hallucinations, delusions, and cognitive impairments. Research has consistently shown that frequent cannabis use, particularly high-potency cannabis, is linked to an increased risk of developing schizophrenia. Younger individuals, particularly males aged 19 to 24, are most vulnerable.

What Happens After Legalisation?

The liberalisation of cannabis laws, particularly in Canada, has led to increased accessibility and use of cannabis products. A 17-year population-based study in Ontario found some startling statistics:

• Between 2006 and 2022, diagnoses of CUD increased by a dramatic 497.4%.
• Among individuals with CUD, the likelihood of developing schizophrenia was significantly higher (8.9%) compared to 0.6% in those without CUD.
• Schizophrenia cases attributed to CUD rose from 1.6% in 2006 to 9.6% in 2022.

These findings suggest that rising prevalence of CUD, combined with the growing potency of cannabis products, may contribute to an increasing proportion of schizophrenia cases attributed to cannabis use.

Key Findings Linking Cannabis Use and Schizophrenia

Increased Schizophrenia Cases Linked to CUD

One of the most significant findings of the Ontario study was the increased proportion of schizophrenia cases associated with CUD. During the pre-legalisation period, 3.7% of schizophrenia cases were linked to CUD. Post-legalisation, this figure jumped to 10.3%. This suggests that cannabis legalisation indirectly contributes to the burden of schizophrenia through the rising prevalence of CUD in the population.

Effects on Younger Age Groups

The research points to a worrying trend among younger populations. Males aged 19 to 24 and females aged 14 to 24 saw an increase in schizophrenia cases attributed to cannabis use. This underscores the vulnerability of adolescents and young adults to the mental health effects of cannabis.

Potency and Availability Matter

With legalisation, cannabis products with higher tetrahydrocannabinol (THC) content—some exceeding 20%—became widely available. Higher THC levels are associated with an increased risk of cannabis use disorder and its associated mental health outcomes, including schizophrenia.

Cannabis Legalisation and Mental Health Trends

Interestingly, while the overall incidence of schizophrenia in Ontario remained stable, diagnoses of “psychosis not otherwise specified” (NOS) rose by 83.7% post-legalisation. This suggests a potential “diagnostic drift,” where cases may shift between related mental health categories.

It’s important to note that the rise in schizophrenia cases linked to CUD wasn’t an overnight change. Researchers found a gradual increase over the years, with no sudden acceleration immediately following legalisation. This indicates that shifting societal norms and the gradual rise in cannabis use over time may play a larger role than the legalisation policy itself.

Implications for Public Health and Policy

Regulation is Key

One of the critical takeaways from this research is the need for robust regulatory frameworks. Governments must ensure that cannabis products, especially high-potency ones, are sold responsibly. Restricting access to minors and implementing strict labelling and testing requirements can help mitigate risks.

Education and Awareness

Raising public awareness about the mental health risks associated with heavy and frequent cannabis use is crucial. Campaigns targeting younger demographics, particularly adolescents and young adults, are essential to safeguard this vulnerable population.

Ongoing Monitoring and Research

The long-term impacts of cannabis legalisation are still unfolding. Continued research is vital to understand how new products and changing consumption patterns influence public health. Monitoring trends in cannabis use, CUD diagnoses, and related mental health conditions like schizophrenia will help shape more effective policies.

What We Can Learn From Canada’s Experience

Canada’s example offers valuable insights for other nations considering cannabis legalisation. While legalisation has provided economic and social benefits, it also highlights the unintended consequences tied to mental health. The rise in schizophrenia cases linked to cannabis use underscores the importance of balancing access with safeguards.

Source: JAMA Network