Cannabis use produces persistent cognitive impairments

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.

These and other acute impairments mirror the residual effects documented for cannabis use, suggesting that the damaging effects of cannabis begin while it is being consumed and persist beyond that period.

"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.