A team of Australian and International scientists just wrapped up the biggest study ever into the genetic predisposition for cannabis use - looking at DNA samples from more than 180,000 people from all over the world.
And guess what? There are 35 genes that can influence you to pick up a joint. Or an apple bong, if that's your thing.
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.
"The genetic variants we examined account for one-quarter of the genetic or inherited influence on cannabis use," Professor Derks said. "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, the 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.
The researchers used a new technique and found that the genes that contribute to developing schizophrenia also make people more likely to use cannabis. Or in other words, people who are genetically predisposed to developing schizophrenia are at higher genetic risk of using cannabis.
Professor Derks says this finding might suggest that people with schizophrenia use cannabis to cope with the symptoms. It doesn't rule out the possibility that cannabis use could also contribute to the onset of schizophrenia; however, they 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." Professor Derks said.
The study was conducted by researchers from the International Cannabis Consortium. It used data from 23andMe, the UK Biobank and 16 other studies.