Cannabis can alter teenagers' brains


CANNABIS CAN physically change the brain and increase the risk of schizophrenia in adolescents who are genetically vulnerable to such effects, a study led by the Royal College of Surgeons in Ireland has found.

It is the first study to show that physical changes to areas of the brain involved in schizophrenia can result from adolescent cannabis use in those with a particular form of a gene, the study’s lead author Dr Áine Behan of the college’s department of physiology said yesterday.

Teenage cannabis use can cause changes to the brain by interacting with the Comt gene, the research, published in the journal Neuropsychopharmacology, found.

A certain form of the Comt gene increases the vulnerability to psychosis and this is heightened by adolescent cannabis use, Dr Behan said.

The Comt gene provides instructions for making an enzyme which breaks down dopamine, the neurotransmitter which controls the brain’s pleasure and reward centres.

The study found that cannabis use in general had a two-fold risk of psychosis but that this was an even greater risk in adolescence.

The study supported previous behavioural research by showing the physical changes in the brain, Dr Behan said.

The study showed that “genetic, developmental and environmental factors interact” to adjust brain function in schizophrenia.

Cell size, density and protein levels were the physical changes shown in three areas of the brain.

The study looked at the effect of acute doses on mice with the particular gene type.

Cannabis use alone is not sufficient to cause the development of schizophrenia and the association may be because of genetic vulnerability to the effects of cannabis, the study suggests. “There needs to be increased knowledge and more research on the effect of cannabis on the brain, including the physical changes,” Dr Behan said.

“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 said.

Having scientific evidence linking cannabis use and psychosis, which shows the mechanism in the brain, was “very important”, Kevin Madigan clinical research fellow with Detect said yesterday.

The Dublin-based service, which treats people with first episodes of psychosis, found that over 60 per cent of clients had used cannabis in the previous year, he said.

The age of first presentation by cannabis users is much lower than those who do not use cannabis, Mr Madigan added.

A study published in the British Medical Journal last year also said that teenagers using cannabis had a higher risk of psychosis.