Study finds no link between smoking cannabis and cognitive decline

New research has concluded that there is no link between smoking cannabis, and experiencing cognitive decline or dementia in old age.

The study was carried out by researchers at Oxford Population Health and the Department of Psychiatry, with their findings published in BMJ Mental Health.

The researchers examined two large groups of people, using data from the UK Biobank (UKB) and the US Million Veteran Program (MVP).

The UKB data came from nearly 19,000 participants who had reported using cannabis in their lives, and they were then split into low and high frequency users.

Low frequency users were those who had smoked cannabis between 1 and 10 times in their life, while high users included anyone who had used it more than 11 times.

The MVP participants were identified from references to ‘cannabis use disorder’ in their health records.

Cannabis use in the older generation has increased hugely in recent years (Getty Stock Images)

According to the researchers, cannabis use amongst the older generation has increased significantly in recent years.

This is largely attributed to the legalisation for medical and recreational use in some countries.

Researchers wanted to find out if cannabis influenced the decline in brain function as the body and brain ages, or whether it worsens conditions like dementia.

The study looked at how the cannabis users fared in five different tests.

These tests included memorising numbers, matching pairs and problem solving.

Their results were then compared with those from a control group of non-cannabis users.

The study found that the cannabis users performed much better than some of the non-users, however the study organisers were keen to stress that this was because the cannabis users from the UKB study came from a higher socioeconomic and educational background than the non-users.

Saba Ishrat was the lead author of the paper, and said: "Although cannabis users performed slightly better on some cognitive tests at baseline, this should not be interpreted as cannabis improving cognition. The differences we observed are more likely explained by underlying demographic, educational and socioeconomic factors that differ between users and non-users, rather than a protective effect of cannabis itself. Our findings underscore the importance of carefully distinguishing association from causation in research on brain health."

The study looked at data from both low and high users (Getty Stock)

Dr Anya Topiwala is a Senior Clinical Researcher at Oxford Population Health and Honorary Consultant Psychiatrist at Oxford Health NHS Foundation Trust, and was involved in the study.

She said "We found no evidence that cannabis use was associated with accelerated cognitive decline or increased dementia risk in older adults."

Dr Topiwala stressed: "However, this should not be interpreted as cannabis being risk-free. Cannabis use is associated with other adverse health outcomes, and further research is needed to understand the effects of higher-dose, long-term use on brain health in later life."

Another recent study looked at the use of 26,362 adults aged 40 to 77 in the UK, and they also said the results were positive but conflicting.

The lead author of the previous study, Anika Guha Ph.D told Medical Press that 'the main takeaway is that the story is nuanced'.

Guha continued: "It's not a case of cannabis being all good or all bad. I think sometimes people have seen my poster on this project or they see the headline and they say, 'Great, I'll just use more cannabis'.

"But it's more complicated than that. I think it depends on how people are using it and what outcomes you're looking at.

"What products are being used, for what reasons, and what part of the lifespan are we looking at? Those are important questions and we're still figuring them out."

Neither study compared how different strains of cannabis reacted, or if there were any differences between CBD and THC.