Genes that increase the risk of developing schizophrenia may also increase the likelihood of using cannabis, according to a new study.
While previous studies have identified a link between cannabis use and schizophrenia, it has remained unclear whether this association is due to cannabis directly increasing the risk of the condition.
The results from the study, led by King’s College London in collaboration with the Queensland Institute of Medical Research in Australia, suggest that part of this association is due to common genes, but do not rule out a causal relationship between cannabis use and schizophrenia risk. The results are published in the journal Molecular Psychiatry.
Cannabis is the most widely used illicit drug in the world, and its use is higher among people with schizophrenia than in the general population. Schizophrenia affects about 1 in 100 people and people who use cannabis are about twice as likely to develop the condition. While the exact cause is unknown, a combination of physical, genetic, psychological and environmental factors can make people more likely to develop the condition.
Previous studies have identified a number of genetic risk variants associated with schizophrenia, each of these slightly increasing an individual’s risk of developing the condition.
The study included 2,082 healthy individuals of whom 1,011 had used cannabis. Each individual’s ‘genetic risk profile’ was measured – that is, the number of genes related to schizophrenia each individual carried. The researchers found that people genetically pre-disposed to schizophrenia were more likely to use cannabis, and in greater quantities than those who did not possess schizophrenia risk genes.
Robert Power, lead author from the Institute of Psychiatry at King’s, said: “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.
“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.”