New research indicates that cannabis use disorder is more strongly associated with the development of mental disorders than previously believed. The study, which includes data from over six million Danes, demonstrates that cannabis use disorder increases the risk of both psychotic and non-psychotic depression and bipolar disorder.
The lead author of the study, Oskar Hougaard Jefsen, a PhD student from Aarhus University, highlights that after accounting for factors such as gender, age, socioeconomics, and family history, cannabis use disorder is linked to nearly twice the risk of developing depression and two to three times higher risk of developing bipolar disorder in both men and women. The findings, published in JAMA Psychiatry, recommend caution regarding cannabis use, especially for individuals at a higher risk of mental illness, and urge policymakers to consider the implications of legalizing cannabis.
Cannabis is one of the most widely used illegal drugs globally, and while previous studies have suggested a connection between extensive cannabis use and an increased risk of schizophrenia, the risk of other mental disorders has been understudied. To address this, researchers from Aarhus University and the University of Copenhagen analyzed data from Danish nationwide registers, including the National Patient Register and the Danish Psychiatric Central Research Register.
The study revealed that one in three Danes under the age of 25 has smoked cannabis, according to the Danish Health Authority. However, the focus of the study was on individuals with significant cannabis consumption who were registered with a substance use disorder, such as those in contact with substance abuse treatment or other healthcare services.
As an increasing number of countries consider legalizing cannabis for medicinal and recreational use, the study’s results have implications for policymakers and discussions surrounding cannabis regulation. The researchers advocate for further research to identify individuals for whom cannabis use is particularly harmful, to inform preventative measures. They also emphasize the need for more knowledge about the dose-dependent effects of cannabis on the brain, cognition, and behavior, as well as identifying risk factors for the transition from cannabis use disorder to psychiatric disorders.
While the study does not provide conclusive evidence that cannabis causes these mental disorders, Jefsen notes that the increased risk observed, even ten years after registering cannabis use disorder, suggests that self-medication alone cannot explain the findings. The study’s unique utilization of Danish register data allows for comprehensive consideration of crucial factors that may affect the results. However, conducting a randomized controlled trial to establish conclusive evidence would be unethical, as it would involve exposing individuals to large amounts of cannabis to determine the long-term risk of mental illness.
