New study links cannabis use to schizophrenia

The results of a new study, published in Nature Neuroscience, show a link between smoking cannabis and psychiatric disorders, including schizophrenia. It is believed that this is the largest genetic evaluation of cannabis use to date.

Researchers from Radboud University, in Nijmegen, the Netherlands, evaluated data collected from more than 180,000 individuals and found that people who had schizophrenia were more likely to use cannabis than those who did not.

The study evaluated data collected by the UK Biobank, results of DNA testing kits submitted to 23andMe by customers, and data previously collected during 16 smaller studies. The research team identified 35 different genes correlated with smoking cannabis, with the strongest correlation with a gene named CADM2.

The lead author of the study, Professor Jacqueline Vink, said that previous studies had identified an association between CADM2 and personality types, risky behaviour, and alcohol use.

The research team looked at more than one million genetic variations, which helped them to understand 11% of the reasons why cannabis use varied between people. Using an analysis technique known as “Mendelian randomisation”, the research team found there were a genetic overlap and a causal relationship between schizophrenia and the risk of smoking cannabis.

The team noted that the analysis revealed that people with schizophrenia smoked cannabis as an attempt to self-medicate. But, the researchers could not rule out the opposite cause-and-effect relationship that smoking cannabis heightened the risk of schizophrenia. The study also revealed a genetic overlap between smoking cannabis and using alcohol and tobacco.