The results chime with previous studies linking schizophrenia and cannabis, but suggest the association may be due to common genes and might not be a causal relationship where cannabis use leads to increased schizophrenia risk.

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.

"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," said Robert Power, who led the study at the Institute of Psychiatry at King's College London.

Schizophrenia is a common and severe psychiatric disorder that affects around one in 100 people. People who use cannabis are about twice as likely as those who do not to develop it.