Newswise — Marijuana is among the globe's frequently utilized illicit substances. Fresh findings propose that the connection between marijuana use disorder and the emergence of mental illnesses is more robust than previously believed.
The analysis incorporates registry information from over six million Danish individuals, and its results reveal that cannabis use disorder heightens the likelihood of both psychotic and non-psychotic depression and bipolar disorder.
"After considering factors such as gender, age, socioeconomics, family history, and more, we observe that cannabis use disorder is linked to nearly double the risk of depression development and a two-to-three-fold higher risk of bipolar disorder development in both males and females," states Oskar Hougaard Jefsen, a PhD student at Aarhus University's Department of Clinical Medicine. Jefsen, the lead author of the study, recently published the findings in the esteemed scientific journal JAMA Psychiatry.
As per the Danish Health Authority, approximately one out of every three individuals under the age of 25 in Denmark has used cannabis. Nonetheless, the recent study specifically concentrates on individuals who have engaged in substantial cannabis consumption to the extent that they have been recorded with a substance use disorder. This includes individuals who have sought treatment for substance abuse or have been in contact with various healthcare facilities.
More countries are legalising cannabis
Numerous studies have provided support for the hypothesis that prolonged and extensive cannabis use poses risks to human mental health. For instance, earlier research indicates that cannabis use disorder can elevate the likelihood of developing schizophrenia. However, investigations regarding the risk of other mental disorders have been limited thus far.
In this particular study, a team of researchers from Aarhus University and the University of Copenhagen conducted an analysis utilizing data obtained from comprehensive Danish nationwide registers. These registers include the National Patient Register, the Danish Psychiatric Central Research Register, and the Danish Register of Pharmaceutical Sales.
Oskar Hougaard Jefsen emphasizes, "This study is the largest of its kind globally, and our findings indicate that cannabis use disorder is connected to a heightened risk of developing depression and bipolar disorder. The results underscore the need for caution regarding cannabis use, particularly for individuals at an elevated risk of mental illness, as well as for policymakers and decision-makers who are deliberating the potential legalization of cannabis."
The trend of legalizing cannabis for both medicinal and recreational purposes is gaining momentum in numerous countries. Since 2018, Denmark has implemented a trial scheme allowing general practitioners to prescribe cannabis-based medications to patients. This initiative also permits companies and individuals to engage in the production of cannabis for medicinal or industrial purposes.
Oskar Hougaard Jefsen holds the view that the findings of the study should be taken into account during discussions surrounding the legalization and regulation of cannabis use. By considering the results, policymakers can make informed decisions regarding the potential risks associated with cannabis and establish appropriate controls to ensure public health and safety.
Oskar Hougaard Jefsen emphasizes the importance of conducting further research to identify individuals who may be particularly susceptible to the harmful effects of cannabis. This would contribute to the development of more effective preventive measures. He also highlights the need for increased understanding of the dose-dependent impacts of cannabis use on the brain, cognition, and behavior, as well as the identification of risk factors associated with the progression from cannabis use disorder to psychiatric disorders. This expanded knowledge would greatly enhance our understanding of the potential risks and enable targeted interventions and support.
No conclusive evidence
Oskar Hougaard Jefsen acknowledges that while the study provides indications and associations between cannabis use disorder and the development of mental disorders, it does not offer definitive evidence of causation. The study highlights a significant correlation, but further research is necessary to establish a causal relationship between cannabis use and these specific mental disorders. It is important to interpret the findings within the context of ongoing scientific inquiry and to consider the limitations of the study in drawing definitive conclusions.
As an illustration, he cannot dismiss the possibility that unacknowledged depression or bipolar disorder has prompted certain individuals in the registry-based investigation to acquire cannabis use disorder - in other words, the condition led to the misuse, not vice versa.
"However, considering the elevated risk of the disease even a decade after the registration of cannabis use disorder, I find it implausible to attribute it solely to self-medication. It appears improbable that numerous individuals would remain undiagnosed for such an extended period," he remarks.
"The Danish register data truly presents a distinctive opportunity to consider numerous pivotal factors that could influence the outcomes. Nevertheless, attaining conclusive evidence would necessitate a randomized controlled trial wherein a cohort of individuals would need to consume substantial quantities of cannabis to observe whether it escalates their long-term vulnerability to mental illness. Yet, conducting such a study would undoubtedly be unethical," he comments.
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