New Danish Study Finds Association between Cannabis Use Disorder and Schizophrenia

A Danish study, published in May 2023 in Psychological Medicine, reviewed nearly seven million Danish health records to study the associations between cannabis use disorder (CUD) and schizophrenia in men and women (1). “Young males might be particularly susceptible to the effects of cannabis on schizophrenia,” the study discussed (1). “Results highlight the importance of early detection and treatment of CUD and policy decisions regarding cannabis use and access, particularly for 16–25-year-olds.”

“We conducted a nationwide Danish register-based cohort study including all individuals aged 16–49 at some point during 1972–2021,” researchers explained (1). “CUD and schizophrenia status was obtained from the registers. The results of this study may inform ongoing policy discussions on legalization and regulation of cannabis use and highlight the importance of targeted public health prevention and intervention efforts.”

“The Danish epidemiology study does not offer hard-and-fast proof of the cannabis-schizophrenia connection, which could be accomplished only through randomized controlled trials,” an article in Scientific American stated (2). “But this link is supported by the fact that marijuana use and potency have risen markedly—from 13 percent THC content in Denmark in 2006 to 30 percent in 2016—alongside a rising rate in schizophrenia diagnoses.” The article also notes the limitations of the study, including lack of data of frequency of cannabis usage and genetic information of the participants (2).

In another article discussing the study, co-author and director of Denmark’s National Institute on Drug Abuse, Nora Volkow, noted that while the Danish population does not have the same diversity as the United States population, the results of the study are enough for everyone to be aware of the risks (3).

“In conclusion, this study finds strong evidence of an association between CUD and schizophrenia among both males and females,” the study stated (1). “Importantly, 15% of cases of schizophrenia in males may be preventable if CUD was avoided. Although CUD is not responsible for most schizophrenia cases in Denmark, it appears to contribute to a non-negligible and steadily increasing proportion over the past five decades. In young males (21–30 years, possibly up to 40), the proportion may even be as high as 25–30%. Our findings underscore the importance of evidence-based strategies to regulate cannabis use and to effectively prevent, screen for, and treat CUD as well as schizophrenia.”

References

1. https://www.cambridge.org/core/journals/psychological-medicine/article/association-between-cannabis-use-disorder-and-schizophrenia-stronger-in-young-males-than-in-females/E1F8F0E09C6541CB8529A326C3641A68
2. https://www.scientificamerican.com/article/heavy-cannabis-use-linked-to-schizophrenia-especially-among-young-men/#:~:text=A%20study%20published%20on%20May,men%20who%20are%20heavy%20users.
3. https://www.bloomberg.com/news/articles/2023-05-04/heavy-marijuana-use-increases-schizophrenia-in-men-study-finds?in_source=embedded-checkout-banner