Smoking cannabis ages the brain by an average of 2.8 years, new research suggests.

This is compared to four years in schizophrenia patients, according to the largest study of its kind. Brain ageing is defined as reduced blood flow through the organ.

Excessive alcohol also ages the organ by 0.6 years, the research adds.

Lead author Dr Daniel Amen, founder of Amen Clinics, said: 'The cannabis abuse finding was especially important, as our culture is starting to see marijuana as an innocuous substance. This study should give us pause about it.'

Reduced brain blood flow has previously been linked to stroke and dementia.

Smoking cannabis ages the brain by an average of 2.8 years, research suggests (stock)

IS MEDICAL CANNABIS LEGAL IN THE UK? Medical cannabis will be available on prescription in the UK after it was approved by the Government in July 2018. Doctors will be able to prescribe medicine derived from marijuana 'by the autumn', the Home Office announced. Home secretary, Sajid Javid, said: 'Following advice from two sets of independent advisors, I have taken the decision to reschedule cannabis-derived medicinal products – meaning they will be available on prescription. 'This will help patients with an exceptional clinical need.' Mr Javid added it is 'in no way a first step to the legalisation of cannabis for recreational use.' This comes after he granted an exceptional licence for Alfie Dingley, six, and Billy Caldwell, 12, to use cannabis for their epilepsy. Possession of the class B drug will still carry an unlimited fine and up to five years in jail, while dealers face 14 years in prison. Advertisement

How the research was carried out

The researchers analysed 62,454 brains scans from 31,227 people.

The scans, which were collected during both rest and concentration, were taken from people aged between nine months and 105 years old to determine factors that contribute to brain ageing.

The scientists analysed the blood flow through 128 regions of each brain to determine how old they thought the individual was.

Once they learnt the person's actual age, they were able to measure the rate of accelerated ageing.

Dr George Perry, from the University of Texas, San Antonio, who was not involved in the study, said: 'This is one of the first population-based imaging studies, and these large studies are essential to answer how to maintain brain structure and function during ageing.'

'We can track disorders and behaviours that age the brain'

Results further suggest bipolar disorder accelerates brain ageing by 1.6 years, while attention deficit hyperactivity disorder (ADHD) speeds it up by 1.4 years.

Perhaps surprisingly, no link was found between depression and brain ageing. The researchers believe the mental-health condition may affect different parts of the brain to disorders such as ADHD and schizophrenia.

Dr Amen said: 'Based on one of the largest brain imaging studies ever done, we can now track common disorders and behaviours that prematurely age the brain.

'Better treatment of these disorders can slow or even halt the process of brain ageing.'

Study author Sachit Egan, from Google, added: 'This paper represents an important step forward in our understanding of how the brain operates throughout the lifespan.

'The results indicate that we can predict an individual's age based on patterns of cerebral blood flow.

'Additionally, groundwork has been laid to further explore how common psychiatric disorders can influence healthy patterns of cerebral blood flow.'

The findings were published in the Journal of Alzheimer’s Disease.