An international team of researchers has conducted the biggest ever study into genetic predisposition for cannabis use and identified 35 genes that influence whether people are likely to ever use the drug.
The scientists also identified genetic links between cannabis use, some mental health conditions and certain personality traits.
The study was co-led by the head of QIMR Berghofer’s Translational Neurogenomics Laboratory, Professor Eske Derks, along with researchers from Radboud University in the Netherlands and Virginia Commonwealth University in the US. It has been published today in the journal Nature Neuroscience.
Professor Derks said the study examined DNA samples from more than 180,000 people worldwide.
“We examined millions of genetic variants and identified 35 genes that influence whether a person is likely to use cannabis during their lifetime,” Professor Derks said.
“Together, the genetic variants we examined account for one quarter of the genetic or inherited influence on cannabis use. Of course, there are also social and environmental factors that contribute to whether a person will use cannabis.”
The researchers also found that there was a genetic overlap between cannabis use and certain mental health disorders, personality traits and use of other substances.
“We found that there was a genetic link between cannabis use, tobacco and alcohol use, risk of developing schizophrenia and bipolar disorder, and certain personality traits including risk-taking behaviour,” Professor Derks said.
“In other words, the genes that increase the likelihood of cannabis use also influence these other traits and conditions.”
The study also examined the link between cannabis use and schizophrenia in more detail.
“Previous studies have shown that there is an association between cannabis use and schizophrenia. It wasn’t known whether using cannabis caused the onset of schizophrenia, or whether schizophrenia caused people to use cannabis, but it was generally thought to be the former,” Professor Derks said.
“In this study, we used a new technique and found that the genes that contribute to developing schizophrenia also make people more likely to use cannabis.
“In other words, people who are genetically predisposed to developing schizophrenia are at higher genetic risk of using cannabis.
“This may suggest that people with schizophrenia use cannabis to cope with the symptoms.
“These findings don’t rule out the possibility that cannabis use could also contribute to the onset of schizophrenia; however, we haven’t found any evidence to support that in this study.
“Our next step is to examine which genes influence how frequently people use cannabis and the amount they use.”
The study was conducted by researchers from the International Cannabis Consortium. It used data from 23andMe, the UK Biobank and 16 other studies.