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An individual’s profile of schizophrenia risk genes is associated with an increased risk of cannabis use. This is the main finding in a paper from an international team of researchers published today as an advanced online publication in the journal Molecular Psychiatry. The findings do not rule out a causal relationship between cannabis use and risk of developing schizophrenia but do suggest that the relationship may also work the other way, i.e. that genetic predisposition to schizophrenia may also increase the likelihood of using cannabis.

Cannabis is the most commonly used illegal drug internationally. In some countries, there is intense debate on the issue of legalising and controlling cannabis use, so increased insight into the health risks associated with cannabis are more pressing than ever. Schizophrenia is a devastating psychiatric disorder which affects about 1% of the population and commonly features auditory hallucinations and delusions. There is substantial evidence to suggest that cannabis is one causal component for schizophrenia, however there is debate around whether this is completely due to cannabis increasing psychosis risk or whether the genes that contribute to increased risk of psychosis also contribute to increased risk of cannabis use.

In an attempt to address this debate, the research team recruited 2082 healthy individuals of whom 1011 had used cannabis. They established the ‘schizophrenia genetic risk profile’ for each person, i.e. the number of genetic variants considered to be predisposing to schizophrenia. The results indicated that individuals who had a genetic predisposition to cancer were more likely to use cannabis and in greater quantities than those who did not have the schizophrenia genetic risk factors.

First author Robert Power, of King's College London, explains the significance of the results: "We know that cannabis increases the risk of schizophrenia. 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." Mr Power concludes: "Our study highlights the complex interactions between genes and environments when we talk about cannabis as a risk factor for schizophrenia. Certain environmental risks, such as cannabis use, may be more likely given an individual's innate behaviour and personality, itself influenced by their genetic make-up. This is an important finding to consider when calculating the economic and health impact of cannabis."

So the debate continues on the complex links between cannabis use and schizophrenia risk and should be an important consideration in discussions of cannabis legalisation.

Power, R.A. et al. (2014). Genetic predisposition to schizophrenia associated with increased use of cannabis. Molecular Psychiatry advance online publication 24 June 2014; doi: 10.1038/mp.2014.51

Press release: King’s College London; available from [Accessed 24 June 2014]