2023-05-11 20:28:29
MONTREAL — Heavy cannabis use appears to increase the risk of schizophrenia, especially in young men, a new Danish epidemiological study warns.
Researchers at the University of Copenhagen examined the medical records of almost seven million people. They concluded that some 3,000 diagnoses of schizophrenia, regarding a third of the total number of diagnoses, might have been prevented if men aged 21 to 30 had not developed problematic cannabis use.
The researchers also note that the quality of marijuana available in Denmark and the number of schizophrenia diagnoses increased simultaneously between 2006 and 2016.
“The first studies to suggest a link between cannabis use, especially in adolescence, and the development of psychosis in adulthood must now be in the twenties, and the data that go in this direction have continued to accumulate,” recalled Dr. Marc-André Roy, who is a full professor of psychiatry and neurosciences at the Faculty of Medicine of Laval University.
The interplay between genes and environment can be complex, he said. But today, researchers are increasingly convinced that excessive cannabis use increases the risk of schizophrenia, not that individuals with a genetic predisposition to schizophrenia become heavy cannabis users.
If we take for granted that there is a causal link, the researchers wrote, in 2021, 15% of cases of schizophrenia would have been avoided in men without excessive cannabis use, and 4% in women.
Among young men, the proportion of schizophrenia cases associated with cannabis abuse that might be prevented might be as high as 25% and even 30%, they added.
It is known that men are greater cannabis users than women, but this is probably not enough to explain the gap between the two sexes, said Dr. Roy.
“There are several aspects of neurodevelopment that are influenced by gender,” he said. There are several phenomena that are powerfully modulated by sex hormones, and that’s kind of always what we think of. But in this study, it goes beyond the fact that boys consume more than girls. At equal consumption, cannabis has a greater effect in men.”
For example, it cannot be excluded that women’s sex hormones protect them from the harmful effects of cannabis. After all, Dr. Roy said, they are less likely than men to experience psychosis, and when they do, it usually happens later in life.
Still assuming a causal link, write the Danish researchers, the results “suggest that men compared to women of the same age may be more susceptible to the psychotogenic effects of cannabis on schizophrenia”. However, they point out, further research will be needed to better understand the mechanisms responsible for this greater vulnerability of young men.
At a population level, say the study authors, problematic cannabis use appears to be an important modifiable risk factor for schizophrenia, particularly for men.
“We know that in populations where higher potency cannabis is used, there seem to be more cannabis-related psychoses,” Dr. Roy said. With hindsight, it begins to satisfy all the criteria. It’s starting to be difficult to say that it has nothing to do with it.”
The findings of this study were published by the medical journal Psychological Medicine.
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