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Published in BMJ Mental Health, this is the largest observational study of relationships between cannabis use and brain structure and function to date and the first to use genetic data to determine whether cannabis causes brain changes.
Cannabis use has increased worldwide following its legalisation for medical and recreational purposes in many countries but the potential long term effects on the brain remain unclear. Previous studies have found that regular cannabis use is associated with a decline in neurocognitive abilities and has had a damaging effect on brain structure and function.
However, these studies have also not been able to pinpoint whether cannabis can actually cause neurocognitive decline or damage to the brain. It is also not currently known whether there is a safe threshold for cannabis use.
In this study, researchers looked at data from 15,896 participants in the UK Biobank study who had undergone a brain imaging (MRI) scan. 3,641 of the participants reported ever using cannabis and 12,225 participants had never used cannabis.
The level of cannabis use among the participants who had reported ever using it varied from once to twice to more than 100 times. These participants were further divided into low frequency users, defined as lifetime cannabis use of up to ten times, and high frequency users defined as lifetime use of 11–100+ times.
The researchers also looked at associations between the participants’ genetic data and likelihood of lifetime cannabis use to more accurately determine whether cannabis use had caused changes in the brain.
Key findings:
- In the observational analysis, cannabis use was associated with multiple measures of changes in brain structure and function;
- Participants who had ever used cannabis had poorer white matter integrity, a part of the brain that is important for cognitive function;
- Neither the duration of cannabis abstinence nor the frequency of cannabis use were associated with any of the observed findings in brain structure and function. There were also no differences between the low and high frequency of consumption groups;
- Most associations were observed in functional connectivity among the men; in women, associations were primarily seen in white matter integrity, suggesting that cannabis use affects men and women differently;
- In the genetic analyses, there were no significant associations between genetically predicted cannabis dependence/abuse or lifetime cannabis use with neurocognitive decline and brain structure and function.
Read the full story on the Department of Psychiatry website.