Cannabis use led to more psychiatric disorders, psychosis and addiction: Study

'Young people ... who engage in daily cannabis use and develop a cannabis use disorder have a higher prevalence of these mental disorders'

Published Jul 02, 2026  •  Last updated 2 hours ago  •  2 minute read

A marijuana plant. Photo by Robyn Beck / AFP / Files /Getty Images

See more Toronto Sun on Google — save as a Preferred Source

Article content

The legalization of cannabis in Canada has not had a positive impact on the mental health of users.

Article content

Article content

In fact, those who smoked pot had a higher chance of being diagnosed with psychiatric disorders, psychosis and addiction, according to a study published in The Lancet Psychiatry.

The authors of the study say youth and young adults are most at risk of mental harms.

“Cannabis use often begins in adolescence and young adulthood, when anxiety, depression, psychosis, and bipolar disorder typically first develop,” the authors said.

“Young people aged in their mid-teens to mid-twenties who engage in daily cannabis use and develop a cannabis use disorder have a higher prevalence of these mental disorders.”

Researchers from the United States, United Kingdom, Germany and Australia searched for evidence from observational and epidemiological studies, clinical trials, and experimental tests to see if there was a biological explanation to the increase in the incidence and prevalence of anxiety, depression, psychosis, bipolar disorders and suicidal behaviours.

Article content

Article content

Read More

1. 

   Nearly half of Canadian youths may be combining drugs with sex: Study

2. 

   Reefer Madness: Cannabis may cause psychosis in Canadian youth, study suggests

Three-fold increase in psychosis

They cited a 2024 analysis that found people who used cannabis, no matter how frequent, were associated with a three-fold increase in the incidence of psychosis.

One hypothesis suggests people who self-medicated with cannabis while experiencing early symptoms of psychosis, such as depressed mood, used it to relieve their symptoms.

The authors said past research found “THC exacerbates symptoms of psychosis and might produce psychotic symptoms in susceptible individuals.”

RECOMMENDED VIDEO

They concluded there is “credible evidence” to suggest regular cannabis use plays some causal role in psychosis.

“There is a consistent association between the frequency and duration of cannabis use and psychosis risk, and a causal relationship is biologically plausible,” they wrote. “The evidence is less clear for anxiety, depressive and psychotic disorders.

Article content

In a separate review of international cannabis policies, The Lancet published a paper that looked at changes to pot legalization over the past 25 years.

Higher rates of addiction after legalization

Their analysis found an increase in pot addiction.

“Commercialized legal markets for non-medical use in Canada and the USA were associated with increased prevalence of cannabis use and cannabis use disorder in adults and increases in cannabis potency since legalization,” those authors wrote.

They said widespread cannabis availability was associated with an increase in hospital admissions for psychosis and for psychotic disorders when patients were diagnosed with cannabis use disorder.

“Poorly regulated legal access to medical cannabis, in the absence of efficacy and safety data, could increase risk of harm,” they said.

Researchers said evidence from Canada and the U.S. found the legalization of non-medical cannabis led to an increase in hospital visits related to psychosis and psychotic events.

Article content