A new study involving over 2,000 participants has found an association between genetic risk factors for schizophrenia and cannabis use, suggesting that the genes predisposing individuals to this psychiatric disorder may also increase the likelihood of cannabis use. The study has been published in Molecular Psychiatry.

Schizophrenia is a mental illness characterized by disturbances in thoughts, perceptions and behavior. During a schizophrenic episode, the individual may experience visual or auditory hallucinations or hold irrational beliefs. It is estimated that around 1 in 100 people will experience an episode of schizophrenia in their lifetime.

An association between cannabis use and this particular disorder has long been observed; cannabis use is significantly higher in individuals with schizophrenia when compared with the rest of the population and cannabis users are almost twice as likely to develop the disorder. However, given that correlation cannot imply causation it has been difficult to discern whether cannabis use directly raises the risk of psychosis.

“Studies have consistently shown a link between cannabis use and schizophrenia,” said lead author Robert Power in a news-release. “We wanted to explore whether this is because of a direct cause and effect, or whether there may be shared genes which predispose individuals to both cannabis use and schizophrenia.”

Although the underlying cause of schizophrenia remains to be discovered, it is thought that a combination of genetic, psychological and environmental factors increases the likelihood of developing the disorder. A number of genes have been implicated in schizophrenia, but could these same genes also increase the risk of cannabis use?

To gain some answers, King’s College London researchers sampled 2,082 healthy individuals, 1,011 of whom had used cannabis. They found a significant association between the burden of schizophrenia risk genes and cannabis use.

Power explains that while this finding cannot rule out the possibility that cannabis use increases the risk of schizophrenia, it suggests that there is likely an association in the other direction as well. In other words, this genetic pre-disposition to schizophrenia also increases the likelihood that the individual will use cannabis.

“Our study highlights the complex interactions between genes and environments when we talk about cannabis as a risk factor for schizophrenia,” adds Power. While we can speculate possible interpretations of the results, given that we are dealing with a correlation the study cannot inform us whether cannabis use increases the risk of schizophrenia or vice versa. What the study does suggest, however, is that cannabis use and schizophrenia may share common genes, which is a very interesting finding.