A large-scale investigation into the genetic predisposition for the use of cannabis shows that cannabis use is related to mental health and personality. The research has been carried out with more than 180,000 participants.

One of the conclusions of this study is that people with susceptibility to schizophrenia are more likely to start using cannabis. The article has been published in Nature Neuroscience on 27 August. The study was conducted by Joëlle Pasman, Karin Verweij and other researchers of the International Cannabis Consortium, using data from large genetic databases of ´23andMe´, ´UK Biobank´ and 16 other studies. It is the largest research worldwide on the hereditary use of cannabis. The researchers found 35 genes that can be associated with cannabis use. The most significant gene, CADM2, was previously associated with risky behaviors, personality and alcohol use. Principal researcher Jacqueline Vink of Radboud University in The Netherlands, leader of the International Cannabis Consortium: 'CADM2 is also strongly associated with the use of cannabis, which fits into this picture.'

Genetic overlap

In this study, all (more than one million) genetic variants together account for about 11 percent of the differences in cannabis use between people. There appears to be a genetic overlap between cannabis use and smoking and alcohol use, mental health (including a greater chance of schizophrenia and autism) and personality (including a greater chance of extraversion and risky behavior). This means that the same genetic variants partially affect cannabis use and other psychological or psychiatric properties.

Cannabis and schizophrenia

The research showed that partially the same genes influence the risk of cannabis use and schizophrenia. 'That is not a big surprise since previous studies have already shown that cannabis use and schizophrenia are related, but we also investigated whether there is a causal relationship,' says Vink. 'With a new analysis technique called' Mendelian Randomization´, we have succeeded in demonstrating that schizophrenic symptoms causally lead to a greater chance of using cannabis'. This may mean that people with schizophrenia use cannabis as self-medication. The reverse causal relationship (that cannabis use could lead to schizophrenia) can not be excluded by the researchers.

The research team has now started a new study, in which they investigate which genes play a role in how often and how much cannabis people use.