Cannabis and Schizophrenia: Implications in the Legalization Era

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The increasing acceptance and legalization of cannabis use worldwide has underscored the need to understand its potential health implications. One area of significant concern is the association between cannabis use and schizophrenia, a severe mental disorder characterized by thought and emotional disturbances. This association is particularly important, given the global burden of schizophrenia, which affects more than 20 million individuals worldwide, according to the World Health Organization.¹

A Mendelian randomization study by Vaucher, et al, provided observational evidence of an increased risk of schizophrenia associated with cannabis use.² Rentero, et al, highlighted the importance of differentiating between cannabis-induced psychosis and schizophrenia for therapeutic purposes.³ Ortiz-Medina, et al, emphasized the need for more research to fully understand the relationship between cannabis use and psychosis.⁴

Urits, et al, found that about 1 in 4 patients with schizophrenia are also diagnosed with cannabis use disorder (CUD), indicating a strong association between cannabis use and psychological disorders.⁵ Marconi, et al, reported a dose-response relationship between the level of cannabis use and the risk of psychosis, suggesting that higher levels of cannabis use could lead to long-lasting psychotic disorders.⁶

García Álvarez, et al, explored the impact of cannabis use on cognitive impairment in schizophrenia and first-episode psychosis, providing further evidence of the potential risks associated with cannabis use.⁷ Cohen, et al, discussed both the positive and negative effects of cannabis and cannabinoids on health, including their association with cognitive alterations, psychosis, and schizophrenia.⁸

In a comprehensive review published in The Lancet, Jauhar, et al, discussed the etiological and therapeutic challenges of schizophrenia, including the role of cannabis as a potential causative factor. They highlighted that cannabis and childhood adversity are areas of debate as causative factors for schizophrenia, emphasizing the need for further research in these areas.⁹

In their review, Lowe, et al, emphasized the need to gauge the potential impact of cannabis legalization on vulnerable populations, such as those with mental illnesses including schizophrenia. They discussed the potential for cannabis to induce long-term psychiatric effects, including the exacerbation of symptoms in individuals with preexisting psychiatric conditions like schizophrenia.¹⁰

Lastly, Hamilton discussed the complex interaction between cannabis, psychosis, and schizophrenia. He highlighted the need for a credible contribution to public health in light of increasing cannabis legalization. His study provided evidence of a dose-response relationship between cannabis use and the risk of psychosis, emphasizing that the risk increases with the frequency of use and the potency of cannabis.¹¹

In light of these findings, clinicians should be aware of the potential risks associated with cannabis use, particularly in patients with or at risk for schizophrenia. Regular screening for cannabis use in these patients may be warranted. Additionally, clinicians should educate patients about the potential risks of cannabis use, particularly in regions where cannabis has been legalized.

Clinicians should also be aware of the potential impact of cannabis use on cognitive impairment in schizophrenia and first-episode psychosis.⁷ Given the potential for cannabis to induce long-term psychiatric effects, including the exacerbation of symptoms in individuals with preexisting psychiatric conditions like schizophrenia, careful monitoring of these patients is crucial.¹⁰

In conclusion, although the acceptance and legalization of cannabis continue to grow, it is crucial to consider the potential risks associated with cannabis use. The association between cannabis use and schizophrenia underscores the need for comprehensive public health policies and education to mitigate these risks. Further research is needed to fully elucidate the complex interaction between cannabis use, psychosis, and schizophrenia.

Dr Ajluni is an assistant professor of psychiatry at Wayne State University in Livonia, Michigan.

From the author: I would like to acknowledge the helpful contributions of ChatGPT in the production of this article. However, I emphasize that I assume full responsibility for the content, including all ideas, arguments, and conclusions presented herein.

References

1. Schizophrenia. World Health Organization. January 10, 2022. Accessed August 1, 2023. https://www.who.int/news-room/fact-sheets/detail/schizophrenia#:~:text=Schizophrenia%20affects%20approximately%2024%20million,%25)%20among%20adults%20(2).

2. Vaucher J, Keating BJ, Lasserre AM, et al. Cannabis use and risk of schizophrenia: a Mendelian randomization study. Mol Psychiatry. 2018;23(5):1287-1292.

3. Rentero D, Arias F, Sánchez-Romero S, et al. Cannabis-induced psychosis: clinical characteristics and its differentiation from schizophrenia with and without cannabis use. Psicosis inducida por cannabis: características clínicas y su diferenciación con la esquizofrenia con y sin consumo de cannabis asociado. Adicciones. 2021;33(2):95-108.

4. Ortiz-Medina MB, Perea M, Torales J, et al. Cannabis consumption and psychosis or schizophrenia development. Int J Soc Psychiatry. 2018;64(7):690-704.

5. Urits I, Gress K, Charipova K, et al. Cannabis use and its association with psychological disorders. Psychopharmacol Bull. 2020;50(2):56-67.

6. Marconi A, Di Forti M, Lewis CM, et al. Meta-analysis of the association between the level of cannabis use and risk of psychosis. Schizophr Bull. 2016;42(5):1262-1269.

7. García Álvarez L, Gomar JJ, García-Portilla MP, Bobes J. Cannabis use and cognitive impairment in schizophrenia and first-episode psychosis. Consumo de cannabis y alteraciones cognitivas en esquizofrenia y primeros episodios psicóticos. Adicciones. 2019;31(2):89-94.

8. Cohen K, Weizman A, Weinstein A. Positive and negative effects of cannabis and cannabinoids on health. Clin Pharmacol Ther. 2019;105(5):1139-1147.

9. Jauhar S, Johnstone M, McKenna PJ. Schizophrenia. Lancet. 2022;399(10323):473-486.

10. Lowe DJE, Sasiadek JD, Coles AS, George TP. Cannabis and mental illness: a review. Eur Arch Psychiatry Clin Neurosci. 2019;269(1):107-120.

11. Hamilton I. Cannabis, psychosis and schizophrenia: unravelling a complex interaction. Addiction. 2017;112(9):1653-1657.