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Adolescent cannabis use impacts cognitive development

Study findings revealed there were concurrent and lasting effects of teenaged cannabis use on important cognitive functions — such as working memory, perceptual reasoning and inhibitory control.

These effects appeared more noticeable for cannabis use than those seen for alcohol, according to the results, published in American Journal of Psychiatry.

“The literature investigating the relationship between adolescent substance use and brain functions is mixed and may depend on how childhood cognitive deficits that exist before the onset of substance use are accounted for in such analyses,” Jean-François G. Morin, BA, from the departments of psychology and psychiatry at University of Montréal, and colleagues wrote. “It is important that new large-scale studies incorporate developmentally sensitive designs that model the impact of year-to-year changes in substance use on age-related changes in cognition.”

Researchers followed a large sample of Canadian high school students from seventh to tenth grade (n = 3,826) to determine the causal and lasting effects of teen substance use on cognitive development at all levels of consumption — abstinent, occasional consumer or high consumer.

They used a developmentally sensitive design to model the relationships between year-to-year changes in cannabis and alcohol use and cognitive development across cognitive domains. Participants were evaluated annually for 4 years on alcohol and cannabis use, recall memory, perceptual reasoning, inhibition and working memory via school-based computerized assessments. Morin and colleagues performed multilevel regression analyses, modeled separately for each substance, to simultaneously test vulnerability (between-subjects) as well as concurrent and lagged (within-subject) effects on each cognitive domain.

Analysis found common vulnerability effects for cannabis and alcohol on all cognitive domains. The results revealed that adolescent cannabis use showed lagged (neurotoxic) effects on inhibitory control and working memory and concurrent effects on delayed memory recall and perceptual reasoning.

Cannabis model results indicated that average frequency of cannabis use over 4 years (between-subject differences) was linked with lower performance on working memory (P = .04), perceptual reasoning (P = .001) and inhibition (P < .01) over the same period, according to the results. The researchers found that “including interactions with time improved model fit only for the perceptual reasoning model and revealed a time-by-within-subject interaction, suggesting stronger within-subject, or concurrent, effects (P < .003) in early adolescence than in late adolescence (P = .03).”

Cannabis effects were independent of any alcohol effects, the researchers reported. Average frequency of alcohol consumption over 4 years was associated with lower spatial working memory performance (P < .05), lower perceptual reasoning scores (P < .01) and more errors on the inhibitory control task (P < .01).

Findings from the combined alcohol and cannabis model revealed that the common vulnerability between working memory and cannabis was not significant over alcohol use and vice versa. According to the researchers, this suggests poor working memory may be a nonspecific common vulnerability to substance misuse in teenage years.

"It will be important to conduct similar analyses with this cohort or similar cohorts as they transition to young adulthood, when alcohol and cannabis use become more severe," Patricia J. Conrod, PhD, from the department of psychiatry at University of Montréal, said in a press release. "This might be particularly relevant for alcohol effects: While this study did not detect effects of teen alcohol consumption on cognitive development, the neurotoxic effects may be observable in specific subgroups differentiated based on the level of consumption, gender or age." – by Savannah Demko

Disclosure: The authors report no relevant financial disclosures.