Cannabis use can shrink the brain

A study published in the British Journal of Psychiatry found those with a family history of schizophrenia saw a shrinkage in the brain after they used the popular recreational drug.

The researchers from Edinburgh University said the findings could help to explain why cannabis use can lead to mental health problems among those already at risk of such problems. Previous studies have found that the brains of people with schizophrenia have structural abnormalities, particularly in a part of the brain called the thalamus.

The brain contains a left and a right thalamus, which are responsible for processing and relaying information.

The Edinburgh researchers studied 57 people aged between 16 and 25, who were well but had a strong family history of schizophrenia.

This put them at a high genetic risk of developing the disease themselves.

Each volunteer had a full assessment, including a magnetic resonance imaging (MRI) scan, at the start of the study.

Two years later, the participants returned for another MRI scan to look for changes to their brain. During this second assessment, they were asked about their use of illicit drugs, such as cannabis, alcohol and tobacco, in the period between scans.

Of the 57 participants, 25 had used cannabis between the two assessments. The researchers found that those people who had used cannabis experienced a reduction in the volume of their thalamus. The loss was found to be “significant” on the left side of the thalamus and “highly significant” on the right side.

No loss of volume was found in those volunteers who had remained cannabis-free during the two-year period.

Some of the participants who used cannabis had also used other drugs, such as Ecstasy and amphetamines.

But even after taking these other factors into account, the link between cannabis use and brain shrinkage remained significant.

The scientists said that the findings could be important in understanding more fully the link between cannabis use and the development of schizophrenia.

Lead researcher Dr Killian Welch said: “Our study demonstrates that cannabis use by people with a family history of schizophrenia is associated with thalamic volume loss.

“This raises the possibility that, when used by people already at elevated genetic risk of the condition, cannabis may increase the likelihood of brain abnormalities associated with schizophrenia developing.”

Dr Welch added: “This may facilitate our understanding of how cannabis use can lead to a worsening of previously subtle symptoms – and ultimately increase the risk of transition to schizophrenia.”

Marjorie Wallace, the chief executive of the mental health charity Sane, said: “This study adds to our understanding of the dangers that cannabis presents.

“Those of us on the front line, including psychiatrists, police and families, know that this drug can be particularly dangerous for the significant minority of people vulnerable to mental illness.

“At Sane, we receive daily evidence that the long-term use of cannabis can trigger frightening psychotic episodes, cause relapse and may bring about mental conditions, such as schizophrenia.

“It can also rob developing young minds of their potential and wreck their futures and those of their families.”