Using cannabis does impair your brain

Cannabis use leads to acute cognitive impairments that may continue beyond the period of intoxication, according to a systematic scientific review published today in Addiction and led by Alexandre Dumais, an associate clinical professor of psychiatry at Université de Montréal.

The meta-review – a review of reviews – merged the findings of 10 meta-analyses representing more than 43,000 participants. The study found that cannabis intoxication leads to small to moderate cognitive impairments in areas such as:

  • making decisions
  • suppressing inappropriate responses
  • learning through reading and listening
  • the ability to remember what one reads or hears
  • the time needed to complete a mental task.

The damaging effects persist

These and other acute impairments mirror the residual effects documented for cannabis use, suggesting the damaging effects of cannabis begin while it’s being consumed and persist beyond that period, said Dumais, who practices at the Institut national de psychiatrie légale Philippe-Pinel.

“Our study enabled us to highlight several areas of cognition impaired by cannabis use including problems concentrating, as well as difficulties remembering and learning, which may have considerable impacts on users’ daily lives,” he said.

“Cannabis use in youth may consequently lead to reduced educational attainment, and in adults to poor work performances and dangerous driving,” said Dumais, a researcher at the UdeM-affiliated Centre de recherche de l’Institut universitaire en santé mentale de Montréal.

“These consequences may be worse in regular and heavy users.”

Especially teens and young adults

Cannabis is the third most consumed psychoactive substance in the world after alcohol and nicotine, with adolescents and young adults being the heaviest users. Recent global changes in the legalization of cannabis suggest there’s now greater public awareness of the drug’s health risks.

It is therefore important to understand the cognitive risks involved in using cannabis, especially to young people, whose brains are undergoing significant developmental changes, Dumais and his research team believe.

“In practical terms, more detailed research is still needed to determine additional cognitive impairments caused by cannabis use,” said UdeM doctoral student Laura Dellazizzo, the study’s first author.

Education to discourage use

“In the meantime,” she added, “preventive and interventional measures to educate youth on cannabis use and discourage them from using the substance in a chronic manner should be considered since youth remain particularly susceptible to the effects of cannabis.”

For their meta-review, the researchers scoured the scientific search engines PubMed, PsycINFO, Web of Science and Google Scholar to establish several categories of cognition: executive functions; learning and memory; attention; processing speed; perceptual motor function; and language.

Only in the area of language did they find no significant difference between users and non-users of cannabis on their ability to process language. They also found no significant long-term residual effects on simple motor skills such as manual dexterity beyond 25 days of not consuming the drug.

About this study

“Evidence on the acute and residual neurocognitive effects of cannabis use in adolescents and adults: a systematic meta-review of meta-analyses,” by Alexandre Dumais et al, was published Jan. 20, 2022 in Addiction.

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