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The proportion of schizophrenia cases linked with problematic use of marijuana has increased over the past 25 years, according to a new study from Denmark.
In 1995, 2% of schizophrenia diagnoses in the country were associated with cannabis use disorder. In 2000, it increased to around 4%. Since 2010, that figure increased to 8%, the study found.
"I think it is highly important to use both our study and other studies to highlight and emphasize that cannabis use is not harmless," said Carsten Hjorthøj, an associate professor at the Copenhagen Research Center for Mental Health and an author of the study published in the medical journal JAMA Psychiatry, via email.
"There is, unfortunately, evidence to suggest that cannabis is increasingly seen as a somewhat harmless substance. This is unfortunate, since we see links with schizophrenia, poorer cognitive function, substance use disorders, etc," Hjorthøj wrote.
Previous research has suggested that the risk of schizophrenia is heightened for people who use cannabis, and the association is particularly driven by heavy use of the drug. Many researchers hypothesize that cannabis use may be a "component cause," which interacts with other risk factors, to cause the condition.
