A new scientific study has linked the smoking of cannabis to certain psychiatric disorders such as schizophrenia.
Researchers at Radboud University looked at data from more than 180,000 people.
They revealed that people with schizophrenia also use cannabis more often.
The large-scale genetic study, published in Nature Neuroscience , was carried out by a team of scientists that is part of the International Cannabis Consortium.
It is claimed that it is the largest genetic study so far to look at the use of cannabis. It used data from the UK Biobank, association results from DNA testing 23andMe clients as well as data from individuals in 16 other smaller study cohorts.
The study identified 35 different genes associated with cannabis use with the strongest associations in a gene called CADM2.
"CADM2 has already been linked to risky behaviors, personality and alcohol use," said Professor Jacqueline Vink, lead author of the study.
For this study, Vink and the researchers were able to view more than one million genetic variants that together accounted for about 11 percent of the differences in cannabis use among people.
One of the biggest correlations that resulted was the genetic overlap between cannabis use and the risk of schizophrenia.
"That is not a big surprise, because previous studies have often shown that cannabis use and schizophrenia are associated with each other, but we also investigated whether this association is causal," Vink explained.
"Our research showed that people with a vulnerability to the development of schizophrenia are at increased risk of using cannabis."
The researchers used an analysis technique called "Mendelian randomisation" to show a causal relationship between schizophrenia and an increased risk of cannabis use.
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This, according to the scientists, indicated that people with schizophrenia use cannabis as a form of self-medication. However, the researchers can not exclude a reverse cause-effect relationship, meaning that cannabis use could contribute to the risk of schizophrenia.
The study also found a genetic overlap between cannabis use and the use of tobacco and alcohol.
There was a similar overlap between cannabis use and personality types that were prone to riskier behavior or that were extroverted.
"This means that genetic variants that influence cannabis use also partially affect other psychological or psychiatric characteristics," the researchers said.