Cannabis use triggers one in three schizophrenia cases among young men

Young men regularly using cannabis are at significant risk of developing schizophrenia, a new study has shown.

Danish-funded research estimated that 25 to 30 per cent of schizophrenia cases among males aged 21-30 may be preventable, if what it called “cannabis use disorder” (CUD) was avoided.

The estimate was based on data derived from the Danish health records of seven million individuals and over 45,000 documented incidents of schizophrenia.


The study found “strong evidence of an association between CUD and schizophrenia among both males and females”, and that cannabis use appears to be contributing to a steady increase in schizophrenia cases in Denmark.

Carsten Hjorthøj, lead author and associate professor at Copenhagen University, said the number of schizophrenia incidents attributable to CUD was much higher in “younger males in whom the brain is still maturing”.

strong evidence of an association between regular cannabis use and schizophrenia

He added: “And we saw that this increase was taking place over time, completely in parallel with the increasing potency of cannabis.”

Prof Hjorthøj hoped the research would inform public debate and challenge the false notion that “cannabis is completely harmless and maybe even something everybody should use”.

The production, distribution, purchase and possession of cannabis have been prohibited by law in Denmark since 1955, although the punishment for possession of small amounts of the drug is typically a fine.

‘Urgent action’ required

Dr Nora Volkow, Director of the US National Institute on Drug Abuse, described the findings of the report – on the “entanglement of substance use disorders and mental illnesses” – a “major public health issue, requiring urgent action.

“As access to potent cannabis products continues to expand, it is crucial that we also expand prevention, screening, and treatment for people who may experience mental illnesses associated with cannabis use.”

Last year, consultant psychiatrist Dr Tony Rao found an astonishing 777 per cent increase in people over the age 55 accessing NHS mental services due to addiction to cannabis over the past 15 years.

According to NHS data published by the Office for Health Improvement and Disparities, the number of over-55s attending treatment for cannabis addiction rose from 374 in 2005-06, to 3,279 in 2020-21.

Also see:


Psychiatrist warns parents of cannabis psychosis link

Cannabis addict speaks of damage done by lifetime of use

Risk of schizophrenia six times higher among teens smoking cannabis