THE use of cannabis during adolescence increases the risk of developing schizophrenia, researchers at the Royal College of Surgeons have found.
The findings are yet more evidence of the mental-health dangers faced by adolescents with developing brains from the so-called "soft" drug.
The most recent figures from the Department of Health show that 8pc of children of school-going age admitted smoking cannabis in the previous year, with 5pc using the drug in the previous 30 days.
Schizophrenia causes a range of different psychological symptoms including hallucinations, delusions, muddled thoughts, changes in behaviour and sometimes failure to distinguish thoughts from reality.
The new research , led by the Royal College of Surgeons in Dublin, shows that adolescents with a particular form of the COMT gene increase their chances of developing schizophrenia.
Dr Aine Behan, the lead researcher, said the cannabis can interact with the gene during adolescence and cause physical changes in the brain.
Although there is no evidence that cannabis causes the schizophrenia it is implicated in physical changes in the brain and increases the risks in certain individuals.
"The brain is still developing during adolescence and cannabis can pose a risk to genetically vulnerable young people," she pointed out.
The research, published in the journal 'Nature's Neuropsychopharmacology', said everyone has this gene but it can be in different forms.
This COMT gene is involved in providing 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, particularly in the brain's reward and pleasure centres.
Dr Behan said: "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.
"It demonstrates how genetic, developmental and environmental factors interact to regulate 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.
"The three areas of the brain assessed in this study were found to show changes in cell size, density and protein levels.
"Increased knowledge on the effects of cannabis on the brain is critical to understanding youth mental health, both in terms of psychological and psychiatric well-being," she added.