Summary: High school–aged girls who use cannabis show greater declines in working memory and academic outcomes than their male peers.
Source: University of Montreal
Early cannabis use harms adolescent working memory, and this effect appears stronger in girls—posing risks to both academic success during high school and memory function into adulthood.
These findings come from research led by Sima Noorbakhsh at the CHU Sainte-Justine Research Centre under the supervision of Professor Patricia Conrod of the Université de Montréal Department of Psychiatry and Addictology.
The study was published in Frontiers in Human Neuroscience in April.
A five-year longitudinal study
Conducted in collaboration with administrators and teachers from 31 high schools in the Greater Montreal area, the project followed 3,826 students over five years. Annual surveys and a battery of neuropsychological assessments were used to evaluate the impact of alcohol and cannabis use on cognitive functioning, including working memory, delayed recall, perceptual reasoning and inhibitory control.
“We collected students’ responses each year across their high school years, allowing us to track changes from the start to the end of secondary school,” Professor Conrod explained.
The longitudinal design and repeated measurements allowed the research team to examine how patterns of substance use related to changes in specific cognitive domains over time, rather than relying on a single cross-sectional snapshot.
Girls more strongly affected
Survey results indicated that both alcohol and cannabis use increased steadily from Grade 7 to Grade 11 for boys and girls. Neuropsychological testing, however, showed differing associations by substance: alcohol use was not linked to large declines in cognitive performance in this sample, while cannabis use was associated with measurable reductions.
Notably, adolescents who began using cannabis early in high school showed declines in test performance, and the negative effect on working memory was significantly greater for girls than for boys.
Why the difference between sexes?
“Working memory—the ability to hold and manipulate information over short periods—is governed largely by the prefrontal cortex,” Conrod said. “The prefrontal cortex matures later than many brain regions, but its developmental timetable differs by sex, with girls typically showing earlier maturation than boys.”
Previous studies have linked early cannabis exposure to altered maturation of the prefrontal cortex. The current findings are consistent with that literature: girls reporting cannabis use in early adolescence exhibited greater working memory deficits by the end of high school compared with girls who initiated use later.
Prevention and public health implications
The study highlights a clear gender difference in how early cannabis use affects brain development, particularly in regions supporting working memory. The researchers observed that by Grade 11—before full adulthood—nearly 80 percent of study participants reported having tried cannabis at some point during adolescence.
Conrod emphasized the real-world consequences: “Statistics Canada data from 2018 showed that more than 10 percent of Canadian teenage girls aged 15 and older reported cannabis use in the past year, and students who use cannabis are more likely to drop out of school.” She added that regular cannabis use is associated with persistent deficits in attention, memory and academic performance.
“Although the law prohibiting marijuana use before the ages of 18 to 21 in Quebec is a good thing, it does not change teenagers’ behaviour,” she said.
The authors call for prevention strategies that actively involve parents, schools and public health agencies and that directly engage adolescents. Early intervention and targeted outreach are needed to protect long-term mental health and educational outcomes.
About this research article
Source: University of Montreal
Media contacts: Press Office – University of Montreal
Image credit: University of Montreal
Original research (open access): “Cognitive Function Impairments Linked to Alcohol and Cannabis Use During Adolescence: A Study of Gender Differences” by Patricia Conrod et al., Frontiers in Human Neuroscience. DOI: 10.3389/fnhum.2020.00095
Abstract
Cognitive Function Impairments Linked to Alcohol and Cannabis Use During Adolescence: A Study of Gender Differences
Adolescence is a period of substantial neurocognitive development and coincides with the onset of substance use for many young people. Existing research has shown that alcohol and cannabis use can impact neurocognitive functioning differently in males and females, but much of that work relies on cross-sectional data with limited repeated measures. To address these gaps, the present longitudinal study examined gender-specific associations between substance use and several cognitive domains. The sample included 3,826 high school students (47% female; mean age 12.7) from 31 schools in the greater Montreal area. Participants completed annual surveys from Grade 7 to Grade 11 assessing alcohol and cannabis use and neurocognitive performance (working memory, delayed recall, perceptual reasoning and inhibitory control). Multilevel linear models evaluated how within-subject changes in substance use related to cognitive outcomes. Findings revealed a significant interaction between gender and within-subject fluctuations in cannabis use: yearly increases in cannabis consumption were more strongly associated with declines in working memory among females than males. Early initiation of cannabis use may therefore produce greater spatial working memory deficits in adolescent girls, potentially undermining academic performance and contributing to longer-term impairments that reduce quality of life in adulthood.