>>Almost a third of schizophrenia cases in young men triggered by cannabis use

Young men with a serious cannabis addiction are at increased risk of developing schizophrenia, a new study suggests.

Experts estimate that nearly one third of cases of schizophrenia in 21 to 30-year-olds were triggered by cannabis use disorder.

Cannabis use disorder is thought to impact around 1 in 200 people, and relates to problematic cannabis use where people cannot control their intake and suffer withdrawal symptoms if they stop taking the drug.

A new study led by Danish researchers analysed the health records of nearly seven million people over 50 years and found a strong link between schizophrenia and serious cannabis addiction.

As many as 30 per cent of cases of schizophrenia among men aged 21 to 30, and 15 per cent of cases in 16 to 49-year-olds, could have been prevented by preventing cannabis addiction, they estimate.

Health concerns ‘require urgent action’

Schizophrenia is a serious mental illness in which people appear to have lost touch with reality.

“The entanglement of substance use disorders and mental illnesses is a major public health issue, requiring urgent action and support for people who need it,” said Dr Nora Volkow, Director of the National Institute on Drug Abuse.

“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.

“The findings from this study are one step in that direction and can help inform decisions that health care providers may make in caring for patients, as well as decisions that individuals may make about their own cannabis use.”

In 2015, a British study estimated that around one in four new cases of psychotic conditions such as schizophrenia could be a direct result of smoking extra-strong varieties of cannabis.

In recent years, many countries and US states have legalised the drug, leading experts to warn that serious psychotic conditions may also increase.

“Increases in the legalisation of cannabis over the past few decades have made it one of the most frequently-used psychoactive substances in the world, while also decreasing the public’s perception of its harm,” said Dr Carsten Hjorthøj, who researches the link between schizophrenia and cannabis consumption at the University of Copenhagen.

“This study adds to our growing understanding that cannabis use is not harmless, and that risks are not fixed at one point in time.”

The authors called for further research to understand why young men seemed more vulnerable to schizophrenia from heavy cannabis use compared with women.

The study was led by scientists at the Copenhagen Research Center for Mental Health at Copenhagen University Hospital, and the National Institute on Drug Abuse, within the US Department of Health.

The new research was published in the journal Psychological Medicine.