Genes that increase a person’s risk of developing schizophrenia may also increase the likelihood of using cannabis, according to a new study led by King’s College London.
Previous studies have shown a connection between cannabis use and schizophrenia, but it remained unclear exactly how the association works. The new study, published in the journal Molecular Psychiatry, suggests that the relationship is more complex than simple cause-and-effect.
“Studies have consistently shown a link between cannabis use and schizophrenia. 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,” said lead author Robert Power from the Institute of Psychiatry at King’s College London.
Cannabis is the most commonly used illicit drug in the world, and its use is even higher among those who suffer from schizophrenia. Approximately one in 100 people will develop schizophrenia, and those who use cannabis are about twice as likely to have the disorder.
Although the exact cause of schizophrenia is unknown, researchers believe that a combination of physical, genetic, psychological, and environmental factors can increase a person’s risk. Previous studies have identified several genetic risk variants associated with schizophrenia, each of these slightly elevating the risk of developing the disorder.
The new study involved 2,082 healthy individuals, 1,011 of whom had used cannabis. Each individual’s “genetic risk profile” was measured — in other words, the number of genes related to schizophrenia carried by each individual.
The findings showed that individuals genetically pre-disposed to schizophrenia were more likely to use cannabis, and use it more heavily than those who did not have the schizophrenia risk genes.
“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 predisposition to schizophrenia also increases your likelihood of cannabis use,” said Power.
“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 behavior and personality, itself influenced by their genetic makeup.
“This is an important finding to consider when calculating the economic and health impact of cannabis.”
Source: King’s College London