Psychiatric researchers look for possible links between cannabis and mental illness

A study released last week identified a connection between an increase in cannabis use disorders and schizophrenia in Denmark.
A study released last week identified a connection between an increase in cannabis use disorders and schizophrenia in Denmark.

Researchers are shining new light on the relationship between cannabis use and a serious mental illness.

A study released last week in the medical journal JAMA Psychiatry identified a connection between an increase in cannabis use disorders and schizophrenia in Denmark, where the study took place. Researchers conducted a data analysis on a group of people including everyone born in Denmark before Dec. 31, 2000, who were 16 years old at any point between Jan. 1, 1972, and Dec. 31, 2016. That gave the researchers a pool of more than 7 million individuals.

The study found that the proportion of cases of schizophrenia associated with cannabis use disorder increased three- to fourfold during the past two decades.

In 1995, about two percent of schizophrenia cases in Denmark could be associated with cannabis use disorder, which is a medical term for cannabis addiction. Since 2010, the percentage of schizophrenia diagnoses associated with cannabis use disorder in Denmark has been between 6 and 8 percent. Researchers speculate that an increase in the prevalence of cannabis use, combined with an increase in cannabis potency over the same time span, is contributing to the rise in schizophrenia associated with cannabis use disorder.

The study from Denmark is far from the first to look at the connection between cannabis and schizophrenia. In 2020, researchers from the California Institute of Behavioral Neurosciences & Psychology systematically reviewed previous studies on cannabis and schizophrenia. Of the 12 studies they looked at, 10 showed a causal link between cannabis use and schizophrenia and eight directly implicated THC as the chemical at fault. Many of these studies found only a causal link between cannabis and schizophrenia among people predisposed to developing schizophrenia even without cannabis use.

Conversely, six of the studies looked at in the California study found that CBD could be beneficial in helping treat schizophrenia.

Recently, as stigma and regulations surrounding the plant have lessened, research has increased. That's important, because as stigma and regulations recede, cannabis use has increased as well. Which has led to a need for better understanding of the plant and its effects. This news from Denmark might not be good news, per se, but it's better than not knowing at all. ♦

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