Cannabis Use Tied to Cognitive Loss in Students

Cannabis use has been tied to concurrent and lasting changes in adolescent cognitive functions, according to a study that tracked Canadian high school students for four years. The story is reported by Judy George, Contributing Writer, MedPage Today

It was cannabis use, and not alcohol consumption, that was linked to lagged changes in inhibitory control and working memory. There was also a pattern of concurrent changes in delayed memory recall and perceptual reasoning. The results were reported by Patricia Conrod, Ph.D., of the University of Montreal CHU Sainte-Justine Research Center, and published in the American Journal of Psychiatry (“A Population-Based Analysis of the Relationship Between Substance Use and Adolescent Cognitive Development”).

“While adolescent use of cannabis and alcohol was tied to generally lower performance in all cognitive domains, ‘of particular concern was the finding that cannabis use was associated with lasting effects on a measure of inhibitory control, which is a risk factor for other addictive behaviors, and might explain why early onset cannabis use is a risk factor for other addictions,’" Conrod said in a statement.

In their study “Conrod and her co-authors followed 3,826 Canadian adolescents who completed an annual online survey to assess cognition, alcohol, and cannabis use (using a 6-point scale that ranged from "never" to "every day") for 4 years, from grades 7 to 11. The researchers looked at relationships between year-to-year changes in substance use and recall memory, perceptual reasoning, inhibition, and working memory and used multilevel regression models to test vulnerability and concurrent and lasting changes in each cognitive domain.”

This study, which is one of the first to track young people's cannabis use while repeatedly testing their cognitive function, brings "a major step-change to what is known about cannabis and mental ability," noted Terrie Moffitt, Ph.D., of Duke University, who was not involved in the research. "The question has been highly controversial, because of concern that legalization will place more cannabis in the hands of more juvenile users," he said.

The average frequency of cannabis use over four years predicted lower performance on working memory. While the average quantity and frequency of alcohol consumption over 4 years was tied overall to lower spatial working memory performance, lower perceptual reasoning scores, and more errors on the inhibitory control task, no within-subject impairment reached significance for any of the cognitive domains studied.”

“Reliance on unverified, self-reported cannabis and alcohol use is an important limitation of the study. The quantity or dose of cannabis exposure also could not be measured. While cognitive function tests were supervised closely by research staff, it would be important to link these results to standardized high school examination scores or other academic outcomes, the researchers noted.”