With marijuana now legalized in Canada, a mental health expert has predicted a significant increase in cannabis-induced psychosis.

The latest figures provided by the Canadian Institute for Health Information (CIHI) reveal a steady rise in cases in recent years.

According to the numbers, 373 people were discharged from hospitals across the country – excluding Ontario and Quebec – after receiving treatment for cannabis-induced psychosis in the 2012/13 fiscal year. That number increased to 723 cases in 2016/17.

CIHI provided CTVNews.ca with data from the Hospital Mental Health Database.

The figures also show that 455 people were discharged in 2013/14, 558 in the year 2014/15 and 616 in the year 2015/16.

Chris Summerville, chief executive of the Schizophrenia Society of Canada (SSC), said his organization will look at U.S. states where marijuana is legal to study what happened there following the end of cannabis prohibition.

“No one should think cannabis is harmless or benign,” Summerville told CTV News Channel from Winnipeg.

"For a number of years we have been seeing more young people coming to use the services of the schizophrenia societies across Canada for cannabis-induced psychosis and schizophrenia. We expect those numbers to increase significantly with legalization.”

In Ontario, the number of discharges for teens aged 12 to 18 rose from 49 in 2012/13 to 66 in 2016/17. The institute didn’t have numbers to represent other age groups in Ontario, and Quebec figures were not available to the CIHI.


Schizophrenia is the most common form of psychosis, affecting between 1 to 1.5 per cent of the population worldwide.

The charity describes psychosis as a break with reality characterized by hallucinations, delusions, impaired thinking and lack of motivation.

Those under 25, those who use cannabis daily, higher potency weed and those who have a family history of mental illness are at greater risk of psychosis, Summerville said.

The Canadian Centre on Substance Use and Addiction has produced a number of reports on the effect of cannabis use.

Its 2016 document, Clearing the Smoke on Cannabis, states that poor mental health is related to chronic cannabis use.

“Studies indicate that chronic cannabis use and an earlier onset of use is associated with an increased risk of developing psychotic symptoms or schizophrenia, particularly among those who might have a pre-existing genetic risk,” the authors said.

“The relationship between cannabis use and psychosis appears to be stronger in people with a predisposition to psychosis, such as those with a family history.”

Reports are mixed on whether population increases in cannabis use coincide with increased rates of schizophrenia.


Academic studies have found that the potency of cannabis has increased from less than 1.5 per cent tetrahydrocannbinol (THC) in the 1970s to up to 28 per cent and higher in 2015. THC is the part of cannabis that makes users feel high.

It has been suggested that more potent strains have led to psychosis at an earlier age and that there are more cases in regions where high potency cannabis is prevalent, as evidenced in results of a 16-year study in the Netherlands and London, England.

The Schizophrenia Society said there is no way to identify who is at risk of developing psychosis with cannabis use and that using marijuana hinders recovery in people already diagnosed with a psychotic disorder.

One study has found that female cannabis users may actually develop an earlier onset of psychosis, according to a 2013 study by researchers in Italy.


The SSC, with the Canadian Consortium for Early Intervention in Psychosis, has created a website to raise awareness about the link between cannabis and psychosis.

“The goal of our education awareness around cannabis use and psychosis is to help young people make informed decisions based upon the evidence and to promote harm reduction," Summerville said.

"The person who has the greatest risk is determined by how young they are, how often they use, and what the potency of the cannabis is they are using. The younger the age, the frequency of use, and the potency of the cannabis place young people at a greater risk."

Last year 2.4 per cent of patients at Ontario’s only 24-hour mental health emergency room, run by the Centre for Addiction and Mental Health (CAMH), were admitted because of cannabis use.

Canada’s 110 mental health clinics for people suffering psychosis for the first time have also seen many patients admitted with cannabis-induced psychosis, CAMH said.

“Before you use, learn all you can about safe use, try to avoid use until you’re in your late teens, avoid high potency and certainly do not use daily,” Summerville told CTV New Channel.

“Those who use daily have a two to three fold greater risk of developing psychosis.”