The alarming connection between cannabis and psychosis has emerged as an urgent issue, with growing evidence linking cannabis use to severe mental health risks. A new, comprehensive study from Ontario, Canada, has investigated the implications of cannabis liberalisation on mental health, focusing on schizophrenia and other psychotic disorders. With data spanning 17 years and involving millions of participants, the findings underline the critical need for action in addressing these concerning trends.

The Long-Term Study and Its Alarming Findings

Between 2006 and 2022, researchers tracked 13,588,681 participants aged 14 to 65 years, all without prior diagnoses of schizophrenia. The focus rested on cannabis use disorder (CUD), a severe form of cannabis dependency, and its association with the emergence of schizophrenia. The results were profound. Nearly 9% of individuals with CUD developed schizophrenia, compared with just 0.6% of those in the general population.

Perhaps the most shocking revelation was the rapid rise in the population-attributable risk fraction (PARF)—the proportion of schizophrenia cases that can be linked to cannabis use. Over the study period, PARF surged from 3.7% to 10.3%. The data strongly suggest that the legalisation and liberalisation of cannabis have contributed to a greater prevalence of cannabis-related mental health issues.

Young males were particularly vulnerable, with nearly one in five schizophrenia cases (18.9%) in those aged 19 to 24 attributed to CUD. This group, already more likely to engage in substance use, faces amplified risks due to their stage of neurological development.

Marijuana and Mental Health Risks

The link between marijuana and mental health extends beyond schizophrenia, with the study identifying significant increases in cases of psychosis not otherwise specified (NOS). This broader term encapsulates various psychoses, which surged by 83.7% following the liberalisation of cannabis laws in Canada.

This rise correlates closely with a staggering 497.4% increase in the diagnosis of CUD. Such figures suggest that broader access to cannabis, compounded by rising THC potency in products, has played a critical role in exacerbating mental health conditions among users. Legalised dried cannabis now often contains THC levels over 20%, a sharp increase from levels seen in previous decades. Highly potent products like edibles and concentrates are particularly concerning, as they increase the likelihood of dependency and acute psychotic episodes.

Age and Gender Disparities in Mental Health Impact

While cannabis use can negatively affect individuals of all ages, the study showed significant differences in impact based on age and gender. Among teenagers and young adults, particularly males aged 14 to 24, the risk of developing psychosis increases sharply with cannabis usage. This group’s vulnerability stems from the fact that their brains are still in crucial stages of development, making them more susceptible to the substance’s harmful effects.

Females within the same age group were also at increased risk, though the figures remained markedly lower compared to their male counterparts. By contrast, older populations demonstrated a reduction in schizophrenia diagnoses, highlighting the disproportionately adverse effect of cannabis use on younger individuals.

Beyond age and gender, socio-economic disparities further compound risks. Individuals in lower-income neighbourhoods experienced higher rates of CUD and associated mental health struggles. Perhaps due to greater stressors or reduced access to educational resources about cannabis’ risks, these communities appear particularly vulnerable to the substance’s long-term impact.

The Broader Implications of Cannabis Liberalisation

The findings from this extensive research reveal the significant public health consequences of cannabis legalisation. Advocates of legalisation often highlight perceived benefits like regulatory oversight, economic gain, or harm reduction. However, the data paints a worrying picture. The number of mental health issues linked to cannabis has risen sharply, threatening to overshadow any possible benefits of policy liberalisation.

During the study period, the overall incidence of schizophrenia was relatively stable. However, schizophrenia rates rose dramatically among younger generations—precisely when high-potency cannabis products became more accessible. This finding calls into question any assumption that legalisation has no harmful effects. For young users, the consequences could be devastating, potentially leading to lifelong struggles with psychotic conditions.

Critically, while legalisation may aim to curb illicit activity, it simultaneously fosters a culture of normalisation around cannabis use. For vulnerable populations, such as adolescents, exposure to such normalisation increases the likelihood of early use, contributing to high rates of dependency and psychosis. These trends necessitate a comprehensive analysis of whether legalisation policies truly align with the goal of improving societal well-being.

Exposing the Real Risks

The study’s results highlight undeniable connections between cannabis use and severe mental health outcomes, demonstrating the escalating need to address these risks. The emphasis on cannabis as a seemingly harmless or recreational substance belies its genuine, long-term risks, particularly for impressionable youth and already disadvantaged populations.

Simple steps like awareness campaigns or medical warnings are inadequate against the scale of the problem revealed in the study. Urgent and more robust interventions might be required, ranging from strict limits on THC potency to tightening regulations around advertising and sales. Any approach must focus on protecting communities from the burgeoning public health crisis.

Why Prevention is Key

Ultimately, the relationship between cannabis and psychosis highlights the critical importance of preventative measures. For policymakers, healthcare providers, and educators, these findings serve as a cautionary tale. They stress the need for immediate steps to restrict cannabis availability, safeguard at-risk groups, and reduce the normalisation of drug use.

Cannabis use isn’t an isolated issue. Its growing connection to psychosis and other mental health crises underscores the wide-ranging effects it can have—not just on individuals, but on families, communities, and health systems at large. This evidence, centred around real-world, long-term data, serves as a crucial reminder to prioritise public health over accommodating commercial interests.

Source: JAMA Network