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The proportion of schizophrenia cases related to problem marijuana use has risen 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 about 4%.
Since 2010, that figure increased to 8%, according to the aforementioned study.
"I think it is very important to use our study and other studies to highlight and emphasize that cannabis use is not harmless," Carsten Hjorthøj, associate professor at the Copenhagen Center for Mental Health Research and study author, said by email. published in the medical journal JAMA Psychiatry.
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"Unfortunately, there is evidence to suggest that cannabis is increasingly viewed as a somewhat harmless substance. This is unfortunate as we see links to schizophrenia, poorer cognitive function, substance use disorders, etc.," he wrote Hjorthøj.
Previous research has suggested that the risk of schizophrenia is increased 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", interacting with other risk factors, to cause the condition.
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"Of course, our findings will have to be replicated elsewhere before firm conclusions can be drawn," Hjorthøj continued.
"But I'm pretty sure we'll see similar patterns in places where cannabis use disorder has increased, or where cannabis potency has increased, as many studies suggest that high-potency cannabis is probably the driving force behind the association with schizophrenia".
Recreational use or problem use
Tens of millions of people use cannabis around the world.
It is legal for recreational use in 19 US states and Canada.
In these and other places, medicinal use is also approved for some conditions.
Cannabis use and cannabis use disorder have increased in Denmark, according to the study, a pattern that is also seen globally.
Recreational use of marijuana is illegal in Denmark, but allowed for medicinal purposes.
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Cannabis use disorder is often defined as problematic drug use: developing tolerance to marijuana;
using cannabis in larger quantities or for a longer period than intended;
not being able to reduce usage;
spending a lot of time getting, using, or recovering from the effects of cannabis;
give up important activities and obligations in favor of cannabis;
and the continued use of the drug despite the negative consequences.
An increase in schizophrenia?
Schizophrenia is a chronic, severe, and disabling mental disorder.
Its symptoms can include delusions, thought disorders, and hallucinations.
Schizophrenia affects 20 million people in the world.
There is no cure, so doctors try to control symptoms with medication and therapy.
While one study has suggested that schizophrenia is on the rise in Denmark, the outlook is uncertain in other countries, Hjorthøj said.
In the United States, the National Institute of Mental Health said it is difficult to obtain accurate estimates of the prevalence of schizophrenia because the diagnosis is complex and overlaps with other disorders.
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"Many psychiatry textbooks state that the incidence ... of schizophrenia is constant over time and independent of geographic location," Hjorthøj said.
"And this has often been used as an argument against the hypothesis that cannabis could cause schizophrenia," he added.
"However, it turns out that there is very little research to support this notion."
The new study was based on data from the Danish national health registry and included all Danish nationals born before December 31, 2000, who were 16 years of age or older at some point from January 1, 1972 to December 31, 2016.
The findings could help explain the "general increase in the incidence of schizophrenia that has been observed in recent years" and provide some support that "the long-observed association between cannabis and schizophrenia is probably partially causal in nature." the study said.
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The study evaluated people who had a clinical diagnosis of cannabis treatment disorder, not general use of the drug, said Terrie Moffitt, professor and president of Social Behavior and Development at the King's College Institute of Psychiatry, Psychology and Neuroscience. London.
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"This nationwide medical records study adds important evidence that patients with a diagnosed cannabis use disorder are at higher risk for psychosis now than before," Moffitt told the Science Media Center in London, which studies the effects of cannabis use. cannabis in the mental health of the baby boomers.
However, Moffitt said that most cannabis users, even those who depend on it, never seek treatment and many people use it recreationally without developing problems.
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"It is known that people seeking treatment tend to have multiple mental health problems, not just cannabis use problems," Moffitt said.
"And there are far more recreational cannabis users who handle it well than there are dependent cannabis users who can't handle it."
In an editorial accompanying the study, Tyler J. VanderWeele, a professor in the Departments of Epidemiology and Biostatistics at Harvard's TH Chan School of Public Health, said the study's estimates could be conservative due to underdiagnosis of cannabis use disorder. .
"Cannabis use disorder is not responsible for the majority of cases of schizophrenia, but it is responsible for an increasing and not inconsiderable proportion. This must be taken into account in discussions about the legalization and regulation of cannabis use." VanderWeele wrote in the editorial.
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