Past studies have shown that those with psychotic disorders tend to use cannabis more than the general population, but “research has been divided over whether cannabis use was the cause of the psychotic disorders," Ragnar Nesvåg, main author of a new study, explains in a press release.
In order to understand whether cannabis abuse can lead to psychosis, genetic risks must also be accounted for.
Therefore, researchers from the Norwegian Institute of Public Health (NIPH), with colleagues from Virginia Commonwealth University, decided to analyze psychiatric interviews of Norwegian twins, which revealed if one or both of the twins had symptoms of psychosis and/or cannabis abuse.
According to the results, twins with symptoms of cannabis abuse had a 3.5 times higher risk of developing symptoms of psychosis than the twin who didn’t abuse cannabis.
“We also tested the hypothesis that symptoms of psychosis caused cannabis abuse, but the hypothesis was less suited to the data. Therefore, it appears that cannabis abuse can be a cause of psychosis," Eivind Ystrom, senior researcher at NIPH, said in the release.
Interestingly, research has also shown that cannabis abuse is highly heritable — as high as 88 percent of the causes behind cannabis abuse can be traced to people having certain risk genes.
With that in mind, the team investigated whether genetic risks and risk of childhood environment could have influenced the link between cannabis abuse and psychosis. However, even after accounting for these risks, the researchers still found that those who abused cannabis had a significantly increased chance of developing psychosis.
Still, the potential risks that accompany cannabis smoking must also be weighed as policy change gears towards decriminalization and legalization.
The full study has been published in the journal Schizophrenia Bulletin.
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