This, researchers say, demonstrates that the causal relationship between cannabis use and schizophrenia might not be clear-cut, and that at least a small part of the association might be caused by genetic overlap, where the same genes that predispose certain people to enjoying weed might also predispose others to developing schizophrenia — or both. The researchers found that people genetically predisposed to schizophrenia were more likely to use cannabis, and to use it in greater amounts than those who had no schizophrenia risk genes. Our study certainly does not rule this out, but it suggests that there is likely to be an association in the other direction as well – that a pre-disposition to schizophrenia also increases your likelihood of cannabis use," said Robert Power, who led the study at the Institute of Psychiatry at King's College London. LONDON Genes that increase the risk of a person developing schizophrenia may also increase the chance they will use cannabis, researchers said on Tuesday after studying more than 1,000 users of the drug. Still, Hill said, the idea that cannabis use and schizophrenia share common genes "is interesting," partly because it highlights a dimension of this relationship that doesn't get a lot of attention. The results chime with previous studies linking schizophrenia and cannabis, but suggest the association may be due to common genes and might not be a causal relationship where cannabis use leads to increased schizophrenia risk.
– The exact nature of the relationship between schizophrenia and cannabis still isn't clear to scientists, but a new study offers additional clues. Researchers studied genetic data on 2,082 people, about half of whom had used cannabis, Reuters reports; they focused on the number of schizophrenia-linked genes in the subjects. The experts found that those with a predisposition to the illness were more likely to use cannabis—and to use more of it—than were those without schizophrenia-linked genes, regardless of mental health history. In other words, says a researcher, the study suggests "a pre-disposition to schizophrenia also increases your likelihood of cannabis use." The Verge explains the complexities of the possible relationship between schizophrenia and marijuana: In the 1960s, for instance, scientists thought that smoking marijuana could cause psychosis in most people; these days, researchers believe using the drug may spur schizophrenia in those who are predisposed to it. The new study effectively turns the idea around, suggesting that those who are predisposed to the illness may also be predisposed to using marijuana. But that doesn't mean weed use doesn't increase schizophrenia risk, an outside expert notes: "Both (theories) may be true."