A new study sheds light on the strong link between a high-cannabis use disorder and mental illness, suggesting a much higher risk than previously thought.
The research, based on data from more than six million Danes, reveals that individuals with cannabis use disorder are almost twice as likely to develop depression and a two to three times higher risk of bipolar disorder. This raises concerns as more countries consider legalizing marijuana.
It is essential to remember that these results do not conclusively prove that cannabis use causes these conditions, as the nature of the study cannot rule out self-medication as a possible explanation.
Great Danish study
The study is one of the world's largest of its kind and provides a comprehensive understanding of use disorders and its link to mental health disorders. The huge amount of data makes the conclusions more reliable than previous smaller studies. In this study, researchers from Aarhus University and the University of Copenhagen analyzed data from Danish national registries such as the National Patient Registry, the Danish Psychiatric Central Research Registry and the Danish Registry of Pharmaceutical Sales.
According to the Danish health authority, a third of Danes under the age of 25 have smoked marijuana, indicating widespread use among young people. However, the research primarily focuses on people with significant levels of consumption. One of the researchers, Oskar Hougaard Jefsen, emphasizes the need for more research to understand whether cannabis has particularly harmful effects on certain individuals. This understanding could give direction to policy and prevention measures with regard to use and legalisation.
The findings indicate that a substance use disorder increases the risk of both psychotic and nonpsychotic depression and bipolar disorder. “When we take into account differences in gender, age, socioeconomic status and family history, and more, we see that a cannabis use disorder is associated with nearly twice the risk of developing depression and a two to three times higher risk of developing bipolar disorder in both men and women,” said Oskar Hougaard Jefsen, a doctoral student in the Department of Clinical Medicine at Aarhus University.
He is the lead author of the study, which was just published in the scientific journal JAMA Psychiatry. According to the Danish health authority, one in three Danes under the age of 25 has smoked cannabis. However, the new study only focuses on people with significant consumption of marijuana, so they are registered as having a substance use disorder – eg because they have been in contact with addiction treatment or other areas of health care.
More countries are legalizing cannabis
Several studies suggest that frequent cannabis use is not harmless to human mental health. For example, previous studies suggest that a cannabis use disorder may increase the risk of developing schizophrenia. But until now, the risk of other mental disorders has been sparsely studied.
“The results recommend caution when it comes to using cannabis. This applies to people with an increased risk of developing mental illnesses, but also to politicians and other decision-makers discussing the possibilities of legalizing cannabis,” says researcher Oskar Hougaard Jefsen.
More and more countries are legalizing the production and sale of cannabis for medicinal and recreational use. Since 2018, GPs in Denmark can write prescriptions for cannabis-based medicines for patients as part of a pilot program that also gives companies and individuals the opportunity to produce cannabis for medicinal or industrial use. Jefsen believes that the results of the study should be considered when it comes to legalization and control.
“We should do more research to see if there are people for whom cannabis is particularly harmful. This could strengthen preventive measures,” he says, adding that there is a particular need to better understand the dose-dependent effects of cannabis use on brain, cognition and behavior, and to identify risk factors for the transition from cannabis use disorder to psychiatric disorders. .
No conclusive evidence
Jefsen points out that, despite the evidence in the study, it does not provide conclusive evidence that cannabis causes these mental disorders. For example, he cannot rule out the possibility that undiagnosed depression or bipolar disorder led some of the people in the registry-based study to develop a cannabis use disorder – ie the illness led to the abuse and not the other way around (self-medication). “But if we see an increased disease risk – even ten years after the cannabis use disorder has been registered – I don't think self-medication can be the only explanation. It seems unlikely that so many people would go undiagnosed for so long.”
“Danish registry data really gives us a unique opportunity to take into account many of the crucial factors that can affect the results. “However, conclusive evidence would require a randomized controlled trial where a group of people would have to smoke large amounts of cannabis to see if it increased their risk of developing mental illness in the long term. Such a study would of course be unethical.”
Source: neurosciencenews.com (EN)
