Schizophrenia Cases Linked to Cannabis Use Disorder Have Increased

A new study suggests the proportion of cases of schizophrenia associated with cannabis use disorder has increased three- to four-fold during the past two decades.

Researchers in Denmark found 2% of schizophrenia diagnoses in that country were linked with cannabis use disorder. By 2000, the rate had risen to 4%. Since 2010, the figure rose to 8%, CNN reports.

“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 study co-author Carsten Hjorthøj. “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.”

In an editorial accompanying the study, Tyler J. VanderWeele of the Harvard T. H. Chan School of Public Health, said that the study’s estimates could be low because cannabis use disorder is underdiagnosed.

“Cannabis use disorder is not responsible for most schizophrenia cases, but it is responsible for a non-negligible and increasing proportion. This should be considered in discussions regarding legalization and regulation of the use of cannabis,” VanderWeele wrote.