Heavy users of marijuana might face an increased risk of bipolar disorder and depression, a new study suggests.
The analysis of more than 6.6 million Danish individuals found that having cannabis use disorder doubled or even tripled the odds for most forms of depression or bipolar disorder. When it came to bipolar disorder in particular, “cannabis use disorder was associated with higher risk for psychotic than non-psychotic subtypes of bipolar disorder,” the researchers noted.
These results, however, cannot prove that marijuana use was the cause of these conditions, the investigators said.
“Our results are compatible with the idea that cannabis may increase the risk of developing depression or bipolar disorder, but we cannot prove this for certain, since we are working with observational data,” explained lead researcher Dr. Oskar Jefsen, from the psychosis research unit at Aarhus University in Denmark. “Unequivocal evidence would require a randomized controlled trial, but this would be unethical.”
Still, one expert noted that while the study can’t prove that cannabis was the cause of bipolar disorder or depression, it adds to growing evidence that the drug is not harmless.
“This is a powerful and well-conducted study that adds to the emerging evidence of the added risk of cannabis regular use to the development of serious mental health disorders,” said Beatriz Carlini, director of the Cannabis Research and Education program and an acting associate professor of psychiatry and behavioral sciences at the University of Washington’s School of Medicine.
As the legalization of marijuana spreads in the United States, people must recognize that cannabis use is not benign, she said.
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