Cannabis Use Produces Persistent Cognitive Impairments

Summary: Cannabis use leads to cognitive impairments that extend beyond the period of intoxication.

Source: Society for the Study of Addiction

A systematic review published today in the scientific journal Addiction has found that cannabis use leads to acute cognitive impairments that may continue beyond the period of intoxication.

This Canadian-led meta-review (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 including:

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

“Our study enabled us to highlight several areas of cognition impaired by cannabis use, including problems concentrating and difficulties remembering and learning, which may have considerable impact on users’ daily lives,” said the study’s co-author Dr. Alexandre Dumais, Associate Clinical Professor of Psychiatry at Université de Montréal.

“Cannabis use in youth may consequently lead to reduced educational attainment, and, in adults, to poor work performance and dangerous driving. These consequences may be worse in regular and heavy users.”

Cannabis is the third most consumed psychoactive substance in the world (after alcohol and nicotine) and adolescents as well as young adults have the highest rates of cannabis use.

Recent global changes in the legalization of cannabis suggest that public perceptions of its safety and acceptability are on the rise.

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

Abstract

Evidence on the acute and residual neurocognitive effects of cannabis use in adolescents and adults: A systematic meta-review of meta-analyses

Background

Cannabis is among the most consumed psychoactive substances world-wide. Considering changing policy trends regarding the substance, it is crucial to understand more clearly its potential acute and residual adverse effects from a public health viewpoint. Cognitive function is one of the targeted areas with conflicting findings. This meta-review measured the magnitude of acute and residual effects of cannabis on cognition in adolescents and adults provided by meta-analyses and evaluated quality of evidence.

Methods

A systematic search was performed in PubMed, PsycINFO, Web of Science and Google Scholar. Meta-analyses were included if they quantitatively examined the performances of users from the general population on cognitive tasks.

Results

The search retrieved 10 eligible meta-analyses (71 effects sizes, n = 43 761) with evidence ranging from low to moderate quality, which were categorized into domains of cognitive functions: executive functions (k = 7), learning and memory (k = 5), attention (k = 4), processing speed (k = 5), perceptual motor function (k = 2) and language (k = 2). Verbal learning and memory displayed the most robust evidence and were most impaired by acute cannabis intoxication that persisted after intoxication passed. Small-to-moderate acute and residual adverse effects were reported for executive functioning. Cannabis use led to small deficits in inhibitory processes and flexibility, whereas small-to-moderate deficits were reported for working memory and decision-making. Evidence regarding processing speed and attention has shown that cannabis administration induced small-to-moderate adverse effects and residual neurocognitive deficits were observed in heavy cannabis-using youths. Results showed no significant difference between cannabis users and non-users on language, and small-to-moderate effects for simple motor skills.

Conclusion

Meta-analytical data on the acute effects of cannabis use on neurocognitive function have shown that cannabis intoxication leads to small to moderate deficits in several cognitive domains. These acute impairments accord with documented residual effects, suggesting that the detrimental effects of cannabis persist beyond acute intake.