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Genetic link between cannabis and schizophrenia discovered

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A new study by an international team of researchers has found that genes that increase an individual’s risk of schizophrenia may also increase his or her use of using cannabis. The findings were published online on June 24 in the journal Molecular Psychiatry.

The study authors note that cannabis is the most commonly used illegal drug worldwide and its use is higher among individuals who suffer from schizophrenia. It is the psychoactive component of marijuana. They explain that the ongoing debate regarding the legalization and control of use has fueled the investigation of its health risks has become a pressing area of research.

Schizophrenia is a common and severe psychiatric disorder, which affects approximately 1% of the population. Cannabis users are twice as likely to develop schizophrenia. The disease usually begins in the late teens or early adulthood; its most common symptoms are disruptions in thinking, language, and perception. Schizophrenia often includes psychotic experiences, such as hearing voices or delusions. The exact cause is unknown; however, current research suggests that a combination of physical, genetic, psychological, and environmental factors can increase the likelihood of developing schizophrenia. Previous studies have reported that a number of genes associated with schizophrenia, each of which slightly increases an individual’s risk of developing the disorder.

Considerable scientific evidence exists that cannabis use increases the risk of schizophrenia; however, it is currently unclear whether this is entirely due to cannabis directly increasing the risk of psychosis or whether the same genes that increases psychosis risk may also increase risk of cannabis use. Therefore, a research team led by Robert Power, PhD at the Institute of Psychiatry at King's College London in the United Kingdom.

Cannabis use has frequently been associated with it, but there is much debate about whether this is because of a direct cause, or whether there may be shared genes which predispose people to both cannabis use and schizophrenia. The study group comprised 2,082 healthy individuals; among them, 1,011 had used cannabis. Each participant’s genetic risk profile, the number of genes related to schizophrenia each of them carried, was measured. The investigators found that that individuals 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. They note that the results underscore the complex interactions between genes and the environment.

The study authors concluded that among a sample of 2,082 healthy individuals, they found an association between a person’s burden of schizophrenia risk genes and cannabis use. The risk was significant both for comparing those who have ever versus never used cannabis and for quantity of use within users. The findings suggest that a portion of the association between schizophrenia and cannabis is due to a shared genetic etiology (cause).

In addition to King’s College London, London, the study authors are affiliated with the University of Queensland (St Lucia, QLD, Australia), VU University, Amsterdam (The Netherlands), Berghofer Medical Research Institute (Brisbane, QLD, Australia), and Washington University School of Medicine (St Louis, MO).