New Delhi: Changes in brains of people consuming cannabis over long-term, including poor white matter connectivity — known to affect cognition — may not have been caused by cannabis, a genetic study has suggested, even as researchers said more studies are needed to understand long-term effects of the drug.
Dried leaves from the cannabis or marijuana plant are smoked or chewed for euphoric effect.
Looking at genetic and MRI brain scan data of nearly 16,000 cannabis users from the UK Biobank dataset, the researchers also found that long-term consumers of the drug had problems in their default mode network, known to be at play while one is letting their mind wander or reflecting.
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However, when the researchers at the University of Oxford, UK, applied methods of analysis to discern direct cause-and-effect links, they found that cannabis did not cause the detrimental changes to the cannabis-consumers’ brains.
Further, the team cautioned that the results, published in the British Medical Journal (BMJ) Mental Health, “need to be interpreted with careful consideration”, and added that more research is needed to understand effects of heavy use and cannabis potency.
Cannabis use is increasing worldwide following its legalisation for medicinal purposes, such as treating chronic pain, in many countries, including high-income ones.
However, legalising the drug for recreational use is being debated around the world, even as countries such as Canada and Germany have legalised its use in limited capacity.
While studies have shown cannabis to negatively affect brain function and structure, potential effects due to long-term use and information regarding a ‘safe threshold’ of drug remain unclear, the researchers said.
Therefore, the team used the analytical technique called ‘Mendelian randomisation’, which looks at genetic variants to know if exposure to a certain risk factor can cause a given outcome.
In this study, genetic variants were analysed to obtain evidence that exposure to cannabis causes changes to brain structure among long-term consumers. Of the entire study group, 3,641 reported ever having used cannabis and 12,225 reported they never used the drug.
Those having ever consumed cannabis were further divided into ‘low frequency’ ones, if they had taken the drug up to 10 times, or ‘high frequency’, if they had consumed it 11 to over 100 times.
The researchers found that effects of consuming cannabis were especially evident in the ‘corpus callosum’ — the main communication route between the left and right sides of the brain.
The affected brain regions, including those involved in the default mode network, were densely packed with cannabinoid receptors, or ‘targets’ for cannabis, the team said.
Further, consuming cannabis was found to affect men and women differently — significant changes were seen in six specific brain regions in men, while among women, the changes were more widespread across 24 structures and regions.
Offering possible explanations for why the study could not establish a cause-and-effect link, the researchers said that unmeasured aspects, such as family history, diet or medications could have influenced past studies.
Further, this study assessed lifelong or long-term effects of cannabis use, whereas previous studies possibly looked at cannabis use at different points in one’s lifetime rather than overall impact throughout the life, they said.
“Cannabis use is associated with differences in brain structure and function. Further research is needed to understand the mechanisms underlying these associations, which do not appear to be causal,” the authors wrote.
