A study published last week in JAMA Psychiatry has revealed a disturbing consequence of marijuana legalisation in the United States, finding that cannabis use amongst people with psychosis increased nearly 10% following legalisation. Moreover, this striking finding sits at the intersection of public health and public safety, directly linking policy changes to increased consumption amongst those most vulnerable to harm.

The research reinforces more than a decade of evidence demonstrating that legalisation lowers risk perception and drives higher consumption rates. Furthermore, the implications are clear: marijuana can cause psychosis, and psychosis endangers entire communities.

Vulnerable Populations Bear the Brunt of Legalisation

The JAMA research highlights a particularly troubling pattern. Specifically, the segment of the population most psychologically vulnerable to marijuana use—both in terms of likelihood to use and adverse reactions—is also most susceptible to the effects of marijuana legalisation policies.

Despite these findings, however, pro-cannabis activists continue pressing for federal legalisation. Indeed, major shifts in state policy began in the 1990s with the rise of “medical” marijuana, as the industry persuaded much of the public and many lawmakers that the drug was not only harmless but beneficial.

Subsequently, that false narrative has fostered a culture of denial amongst advocates who refuse to acknowledge the growing body of research linking marijuana to serious health risks. As a result, vulnerable individuals have been left exposed to increased harm without adequate protection or warning.

The Changing Tide of Public Opinion on Marijuana Legalisation

“Big Marijuana” built its campaign for liberalisation on a foundation of misinformation about the drug’s harms. Advocates used this narrative to push through ballot measures and legislation for recreational use throughout the 2010s. Nevertheless, what began as a wave of victories in states such as Colorado and California has since stalled significantly.

In fact, marijuana legalisation has been defeated in seven of the last 10 state initiatives, signalling a fundamental shift in public sentiment. The tide is turning because the public is beginning to recognise the true costs of legalisation.

A recent Gallup poll between 2022 and 2024 revealed a 10-point reduction in the number of Americans who thought marijuana had a positive effect on those who use it, dropping from 53% to 43%. This decline in support likely reflects growing public recognition of the drug’s harms, particularly as legalisation and commercialisation have normalised use.

Scientific Evidence Links Cannabis to Severe Mental Health Risks

The connection between marijuana legalisation and psychosis is supported by extensive scientific research. Study after study demonstrates that increased marijuana use, beginning in adolescence or later, makes it far more likely that someone will develop schizophrenia or a form of psychosis.

Moreover, those experiencing psychological distress often turn to marijuana for relief, encouraged by marketing that downplays its risks. The industry has little incentive to be transparent, especially about the dangers of heavy use or high-potency products.

Advocates once promised that legalisation would pose no threat to public health. However, both new research and lived experience tell a different story. Vulnerable populations are visibly paying the price as normalised marijuana use contributes to increased rates of serious mental health conditions.

The Marketing Machine Behind Cannabis Normalisation

The cannabis industry has employed sophisticated marketing strategies to promote their products whilst minimising discussion of health risks. Furthermore, without stronger accountability measures—such as clear health warnings and potency limits in legal states—this pattern is unlikely to change.

The parallels to historical tobacco industry tactics are evident. Similarly, tobacco companies once promoted their products as harmless or even beneficial, whilst deliberately obscuring evidence of serious health risks. Today, the marijuana industry follows a comparable playbook, prioritising profits over public health.

Policy Implications and the Path Forward

Policymakers should treat marijuana legalisation and psychosis risk as a serious public health issue, not merely a cultural or political symbol. Therefore, this requires stronger regulation where cannabis is legal, honest messaging about risks, and a willingness to confront the uncomfortable truth that legalisation has tangible consequences.

In addition, states that have legalised marijuana must implement robust protections for vulnerable populations. These should include mandatory health warnings, potency limits, restrictions on marketing, and increased funding for mental health services.

Moreover, federal authorities must resist pressure to legalise marijuana nationally until adequate safeguards can be established. The evidence from states that have already legalised clearly demonstrates the risks, particularly for individuals with pre-existing mental health vulnerabilities.

Addressing the Mental Health Crisis

The intersection of marijuana legalisation and psychosis represents a growing mental health crisis that demands immediate attention. Consequently, public health campaigns must educate communities about the genuine risks associated with cannabis use, particularly amongst adolescents and those with family histories of mental illness.

Furthermore, healthcare providers require better training to identify and address marijuana-related mental health issues. Early intervention can make a significant difference in outcomes for individuals developing psychosis or other serious conditions linked to cannabis use.

Ultimately, the research published in JAMA Psychiatry serves as a wake-up call. It’s time to act on what the data clearly shows: marijuana legalisation has serious consequences for mental health, and vulnerable populations are suffering as a result. Policymakers can effectively address these harms only by implementing evidence-based policies, providing honest public education, and enforcing strong regulatory frameworks.

Source: Unherd