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Cannabis Use Doesn’t Affect the Brain’s White Matter, Study Finds

By Leo Bear-McGuinness

Published: Sep 03, 2021   
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While it’s known that heavy cannabis use can alter how the brain functions, it doesn’t seem to change the organ’s structure, according to new research.

Published in Addiction Biology, the study found that the white brain matter of daily cannabis consumers and the matter of non-smokers didn’t significantly differ.

The surprising findings imply that cannabis use doesn’t significantly affect the physical order of the human brain. However, as all the participants in the study were aged between 18 and 25, the authors of the study say that the brain structure of adolescents could still be vulnerable to marijuana’s effects.

THC in the membrane

To make their conclusions, the researchers from the universities of Rotterdam, Amsterdam, and Melbourne first recruited 39 daily cannabis consumers (most of whom met the criteria for cannabis use disorder, CUD) and 28 participants who didn’t use the drug.

To minimize the impact other factors could have on their brain matter, the participants were also screened to ensure they all consumed cigarettes, alcohol, and psychoactive substances at similar levels.

The brains of the participants were then scanned using an MRI (magnetic resonance imaging) machine.

After analyzing the results, the researchers found that all major measurements from the MRI scans were largely similar between the cannabis consumers and the control group. The cannabis consumers who began their habit at a younger age did tend to have lower levels of fractional anisotropy (FA) – a measurement used to infer the density of neurons in the brain – but these levels were still within an acceptable range of the control group’s measurements.

“These results suggest that near-daily cannabis use does not necessarily influence white matter microstructure in young adults, but, in line with previous findings, those starting weekly use relatively young may be at an increased risk,” the researchers concluded in their study.

What’s the matter?

Another recent study that did examine the brains of teenagers found that adolescent cannabis use can reduce the thickness of certain brain regions.

Published in JAMA Psychiatry, the study analyzed the brain scans of 799 teenagers and determined that, on average, the left and right prefrontal lobes of the teens who had consumed cannabis were thinner than those of the teens who hadn’t used the drug.

As these brain regions help control motor function, problem solving, memory, and many other functions, the researchers said that their findings “underscore the importance of further longitudinal studies of adolescent cannabis use, particularly given increasing trends in the legalization of recreational cannabis use.”

Other research has linked teenage cannabis use to changes in the developing brain and an increased risk of depression and suicidal ideation. Teens who “dab” cannabis concentrates, which are often stored in dab containers, are also more likely to consume cannabis frequently, according to a paper published last year.

Regarding adult brains, several previous studies have tried to determine whether cannabis use changes white matter structure to inconsistent results. Some studies found that individuals with CUD had lower FA readings, while other studies found no differences between the results of CUD participants and the controls.

However, according to the authors of the recent Addiction Biology paper, many of these previous studies failed to fully account for other factors that could alter brain structure, such as mental health disorders and alcohol use.


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