Cognitive Effects of Cannabis on Youths Are Short-Lived, Meta-Analysis Finds

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A literature review published yesterday in the JAMA Psychology journal bears some good news for anyone concerned about the effect of cannabis on young brains.

“Results indicate that previous studies of cannabis in youth may have overstated the magnitude and persistence of cognitive deficits associated with use.”
JAMA Psychology Journal

Researchers at University of Pennsylvania’s Perelman School of Medicine reviewed 69 studies of cognitive function in adolescent and young-adult cannabis users performed between 1973 and 2017, and found “a small overall effect size for reduced cognitive functioning associated with frequent or heavy cannabis use.” The participant’s age and the age when they began using cannabis had no effect on this.

Perhaps most importantly, researchers found that even that small impact was rendered insignificant by a 72-hour abstinence period. “Although continued cannabis use may be associated with small reductions in cognitive functioning,” the authors concluded, “results suggest that cognitive deficits are substantially diminished with abstinence.”

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In other words, smoking cannabis—even when your brain is still developing—doesn’t make you significantly dumber. And whatever effect it does have wears off after just three days.

It’s worth noting that some studies have found an association between early cannabis use and increased incidence of psychosis. The JAMA paper did not look at psychosis, only cognitive impairment.

It would seem that the “perma-fried” pothead was just another prohibition era myth, but it’s one that demonstrates why the results of this study are so important: That myth was widely accepted by even the pro-legalization community. However, as the study concludes, “results indicate that previous studies of cannabis in youth may have overstated the magnitude and persistence of cognitive deficits associated with use.”

It’s worth noting, however, that some studies have found an association between early cannabis use and increased incidence of psychosis. The JAMA Psychology paper did not look at psychosis, only cognitive impairment. That said, this is still great news for anyone worried about what effect their “extracurricular” activities in high school may have had on their brain.

As NORML’s deputy director, Paul Armentano, put it, “These findings should help to assuage fears that cannabis’ acute effects on behavior may persist long after drug ingestion, or that they may pose greater potential risks to the developing brain.” Phew!