Lifetime cannabis use is linked to changes in brain structure and function, but might not be the cause of these changes, a new Oxford study has found.

Research from Oxford Population Health and the University of Oxford’s Department of Psychiatry explored the long-term effects of cannabis on the brain.

Cannabis use has increased worldwide following its legalisation for medical and recreational purposes, but the potential long-term effects on the brain remain unclear.

Previous studies have not been able to pinpoint whether cannabis can cause neurocognitive decline or damage to the brain, and it is also not currently known whether there is a safe threshold for cannabis use.

The Oxford study was the largest of its kind, examining relationships between cannabis use and brain changes.

It was also the first to use genetic data to investigate whether cannabis directly causes these changes.

The research found cannabis use was linked to multiple changes in brain structure and function.

It also found participants who had used cannabis had poorer white matter integrity, a part of the brain that is important for cognitive function.

Dr Anya Topiwala, an honorary consultant psychiatrist at Oxford Health NHS Foundation Trust, and Professor Klaus Ebmeier, a professor of old age psychiatry, supported the research.

The study, Association between cannabis use and brain structure and function: an observational and Mendelian randomisation study, has been published in BMJ Mental Health.