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Cannabis Worsens Verbal Learning and Memory, Review Finds

By Leo Bear-McGuinness

Published: Jan 24, 2022   

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Cannabis Worsens Verbal Learning and Memory, Review Finds

Frequent cannabis use can impair a person’s memory and level of verbal learning, according to a new review.

Published in the journal Addiction, the review also found that cannabis use reduces a person’s ability to make decisions and their working memory.

The authors of the review say that health professionals should be aware of these cognitive risks and watch out for “problematic” cannabis use among their patients.


Do you remember?

To assess how cannabis affects cognition and memory, the researchers from the Université de Montréal, Canada, reviewed ten existing literature reviews that, in total, represented studies on more than 43,000 participants.

This meta-review (a review of reviews) found that cannabis has mild detrimental effects on a person’s ability to concentrate. It also provokes mild-to-moderate detriments to a person’s processing speed (how quickly they can think).

Small-to-moderate reductions were found in executive functioning (a person’s direct control over their thinking), following cannabis use.

Small deficits to a person’s cognitive flexibility (the ability to adjust to change) were also observed, along with moderate deficits to working memory (the ability to recall recent memories) and decision making.

But the most damaging cognitive effect of cannabis, according to the review, is to verbal memory.

“This diminished ability to learn, retain and retrieve verbal information may have repercussions for users’ occupational functioning, independent living and ability to navigate through their daily life adequately,” the authors wrote in their meta-review.

The ability to process language was the only cognitive area apparently unaffected by cannabis use; no significant differences were observed between cannabis consumers and non-consumers.

The researchers also concluded that cannabis has no significant long-term effects on simple motor skills, such as manual dexterity, beyond 25 days after use.

The authors do recognize that their meta-review has its limitations, though. For one, many of the reviewed studies didn’t take note of how often or how much participants consumed cannabis – factors which could further elucidate marijuana’s cognitive effects. Most of the studies’ sample sizes were also very small and comprised of young, healthy adults – factors which could limit the generalizability of the results.

Nonetheless, the research team say that their meta-review findings still demonstrate that cannabis use can have detrimental effects on a person’s level of cognition, particularly if they are young and a frequent consumer.

“Cannabis use in youth may consequently lead to reduced educational attainment, and in adults to poor work performance and dangerous driving,” Alexandre Dumais, an associate clinical professor of psychiatry at Université de Montréal, said in a statement.


Cannabis and memory

Many of the meta-review’s findings are hardly surprising; it’s widely known that cannabis can impair a person’s memory and their ability to recall information – it’s the basis of many stoner stereotypes.

One study published in 2020 even found that intoxicated cannabis users were more likely to remember false memories. In a series of virtual reality situations and memory tests, cannabis consistently increased the chances of a participant recalling a detail that was never there.

But how could cannabis be causing so many cognitive affects? In their meta-review, Dumais and his team posit that the drug may disrupt a person’ ability to focus by interacting with the brain’s CB1 receptors, which can be found in the pre-frontal cortex and medial temporal region.

 

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