One of the arguments used all across the world against the legalisation of cannabis, that its use leads to increased cases of schizophrenia and psychosis, was dealt a blow this week. Evidence from a Canadian study shows that hospital admission for cases of cannabis-induced schizophrenia and psychosis have not risen since the Canadian government legalised adult cannabis use in 2018.  

In the study, published in the Canadian Journal of Psychiatry, researchers state that they aimed to directly address the often reported fear “that legislation might increase the burden of transient and persistent psychotic illnesses in society.”

By analysing Emergency Room (ER) data collected from the provinces of Ontario and Alberto in Canada, and then using a method of analysing data called SIMIRA, researchers assessed the associations between Canada’s legalisation of cannabis on October 17th 2018 and weekly presentations of (the Canadian medical authorities definition of) cannabis-induced psychosis and schizophrenia. Researchers also studied ER admissions of amphetamine and alcohol-induced psychosis for comparison.

When the data was examined, researchers discovered that between April 2015 and December 2019 admissions to ER presenting symptoms of cannabis-induced psychosis and schizophrenia had doubled. However, when the SARIMA model for interpreting data was applied they did not find any “evidence of significant step-function effects associated with cannabis legalization on post-legalization weekly ED counts…” of cannabis-induced psychosis or schizophrenia. Alcohol and amphetamine-induced psychosis admissions to ER also did not increase when examined in the same way. 

The study concludes, “implementation of Canada’s cannabis legalization framework was not associated with evidence of significant changes in cannabis-induced psychosis or schizophrenia ED presentations. Given the potentially idiosyncratic rollout of Canada’s cannabis legalization, further research will be required to establish whether study results generalize to other settings.”