A comprehensive study examining over 12 million individuals in Ontario has revealed alarming trends in mental health among adolescents. Psychosis in young Canadians has increased by 60 per cent over recent decades, and researchers are investigating the role of cannabis.

The research, published in The Canadian Medical Association Journal, identifies a dramatic surge in psychotic disorders among teenagers and young adults. This trend prompts urgent questions about substance consumption and deteriorating youth mental health.

Psychosis in Young Canadians Reaches Alarming Levels

Between 1997 and 2023, new psychosis diagnoses among people aged 14 to 20 jumped by 60 per cent. Meanwhile, diagnoses in older age groups remained stable or declined. The data shows that individuals born in the early 2000s face twice the risk of receiving a psychotic disorder diagnosis by age 20 compared to those born in the late 1970s.

Dr Daniel Myran led the investigation. He works as a family physician and research chair at North York General Hospital. “I was expecting to see some increases in these younger folks, but I was quite surprised by the scale,” he stated.

Of the 12 million people studied, 0.9 per cent received a psychotic disorder diagnosis during the study period. This seemingly small percentage translates to roughly 108,000 individuals affected.

Cannabis Use and Psychotic Disorders Among Youth

The timing of increased psychosis in young Canadians coincides with significant changes in drug accessibility. Canada legalised cannabis in 2018. Since then, cannabis usage among Canadian youth has risen steadily.

Recent surveys reveal that 41 per cent of Canadians aged 16 to 19 reported using cannabis at least once in 2024. This figure represents a jump from 36 per cent in 2018, the year of legalisation. The five percentage point increase may seem modest, but it represents thousands of additional young users.

Dr Myran’s research was partially motivated by concerns that cannabis legalisation might elevate rates of schizophrenia and related conditions. “I think that there is a group of individuals who develop psychosis because of substance use, who in its absence would not have,” he explained.

The study’s authors acknowledge that rising cases could stem from multiple factors. These include older paternal age, migration-related stress, neonatal health complications, and improved early intervention programmes. However, researchers cannot ignore the correlation between increased substance availability and rising mental health diagnoses.

How Psychotic Disorders Among Youth Affect Brain Development

The developing adolescent brain may be particularly vulnerable to regular substance use effects. Dr Myran suggested that consistent use during formative years might trigger rewiring or structural changes in the brain.

“Your brain is quite plastic, and if we have substance use that’s causing hallucinations, if you have ongoing activation and firing and that kind of stuff, it can change your brain,” he noted. He referenced the neurological principle that neurons which fire together wire together.

The Ontario study examined schizophrenia alongside related diagnoses. Schizophrenia is a severe disorder characterised by delusions and altered thinking. The largest increase appeared in cases classified as “psychosis not otherwise specified”. Doctors use this category when psychotic symptoms are evident but they cannot definitively diagnose schizophrenia.

International Patterns of Psychosis and Beyond

Northern Europe has reported increases in psychosis among young people. However, researchers have not documented similar trends in the United States. Dr Dost Ongur serves as chief of the division of psychotic disorders at McLean Hospital near Boston. He described the Canadian analysis as “an outlier in showing a sharp rise in new cases.”

Dr Deepak D’Souza, a professor of psychiatry at Yale, acknowledged important implications. The findings “suggest that psychosis may be occurring more frequently, being detected earlier by the health system, or both,” he said. He emphasised that any evidence indicating an increase in psychosis “is both alarming and deserving of careful scrutiny.”

Scientists have long debated whether cannabis use causes psychotic disorders or merely accompanies them. Substance use often occurs alongside other stressors. These stressors constitute known risk factors for psychosis. Some individuals with psychotic disorders may use cannabis to manage their symptoms, further complicating the relationship.

What the Data Tells Us About Psychotic Disorders Among Youth

Canada’s universal healthcare system provides researchers with comprehensive data on medical care across the entire population over time. This advantage enables detailed comparisons between birth cohorts. The data advantage may explain why researchers have not yet identified similar trends in countries without universal healthcare coverage.

Dr Kevin Gray works as a specialist in bio-behavioural medicine at Medical University of South Carolina Health. He praised the study’s methodology whilst cautioning that replication across other jurisdictions would be essential. “We don’t have the smoking gun to say this is the mechanism,” he stated.

Psychotic disorders are heavily genetic. Their prevalence typically remains stable at approximately 1 per cent of the population. However, researchers isolated young people from the overall population and found striking differences. As psychosis diagnoses among youth rose, rates among older people declined. This pattern effectively masked the trend in aggregate data.

Understanding Rising Psychosis

The findings underscore the critical importance of understanding how substance availability affects developing brains. The consumption patterns matter tremendously. Young people’s brains continue developing well into their mid-twenties, making them particularly susceptible to external influences.

When researchers separated the data by age group, they uncovered a troubling pattern. Older Canadians showed declining rates of new psychosis diagnoses. Yet younger Canadians experienced the opposite trend. This divergence suggests that factors specific to younger generations drive the rise in psychosis in young Canadians.

Future Research on Psychotic Disorders Among Youth

Dr Myran emphasised that the results point to an urgent need for further research. Scientists must understand how expanding cannabis use among young people affects mental health outcomes. The central question remains unanswered. How much psychosis stems from modifiable substance use?

“Are these edge scenarios, where it’s pretty rare? Or is it actually quite frequent?” Dr Myran asked. This question highlights the need for definitive answers to guide public health policy and youth protection strategies.

The study examined people born in Ontario between 1960 and 2009. This 50-year span allows researchers to track trends across multiple generations. The scale of the study strengthens its findings and makes the observed trends harder to dismiss.

As evidence continues to emerge, the study serves as a stark reminder. Increased substance accessibility without corresponding awareness of developmental vulnerabilities carries potential consequences. Young people deserve protection during their most formative years.

The research raises important questions for parents, educators, and policymakers. Understanding the link between substance use and mental health outcomes becomes increasingly crucial. Early intervention and education may help protect vulnerable youth from preventable harm.

Source: nytimes