Early cannabis use increases schizophrenia risk

Some young people who use cannabis are at greater risk of developing schizophrenia, according to new research.

According to the report, people who have a particular form of the COMT gene were more susceptible to developing schizophrenia.

It was conducted by a team of specialists from the Royal College of Surgeons in Ireland and was published in international academic journal Nature’s Neuropsychopharmacology.

Lead author Áine Behan, from the RCSI department of physiology, said the risk rose if these people smoked cannabis in adolescence.

Researchers were able to demonstrate that early cannabis use among this group actually physically altered their brains — a change that is long term.

“It has previously been seen that people with a genetic vulnerability can develop schizophrenia and psychosis, and this risk increases if smoking cannabis during adolescence,” said Dr Behan. She said the research pushed the evidence further.

“This is the first study to show that the combined effects of the COMT gene with adolescent cannabis use cause physical changes in the brain regions associated with schizophrenia.”

Dr Behan said the study demonstrated that the combination of the gene and adolescent cannabis usage increased the risk of developing schizophrenia.

“It demonstrates how genetic, developmental, and environmental factors interact to modulate brain function in schizophrenia, and supports previous behavioural research which has shown the COMT gene to influence the effects of adolescent cannabis use on schizophrenia-related behaviours,” she said.

Her team examined three areas of the brain and found changes in cell size, density, and protein levels.

“The physical changes are long-term,” said Dr Behan.

“They are seen in adult brains following use of cannabis during adolescence.”

The COMT gene provides instructions for making enzymes which break down a specific chemical messenger called dopamine. Dopamine is a neurotransmitter that helps conduct signals from one nerve cell to another.

Dr Behan said that the research was not intended to be “scare-mongering”, but was aimed at raising awareness.

“Increased knowledge on the effects of cannabis on the brain is critical to understanding youth mental health, both in terms of psychological and psychiatric wellbeing,” she said.

Dr Behan stressed that the report was not saying that all cannabis users faced an increased risk of developing schizophrenia, as her study only examined people with a genetic susceptibility.

* Full report on

www. rcsi.ie