Many studies have shown that alcohol and cannabis use can lead to cognitive impairment. A new study collected data from adolescents and studied their substance use patterns and cognitive maturation continuously for 5 years. This population-based study included 3,826 seventh-graders as a part of a drug and alcohol prevention program.
At the start of the study, each student completed an anonymous questionnaire on his or her substance use. Then, once a year they continued to provide updated data including if they had used substances, which substances they were using, and the frequency of use. They were also tested on cognitive measures each year.
The results were analyzed and then categorized into three models: cannabis, alcohol, and combined cannabis and alcohol use. The cannabis data showed that the average cannabis use lead to lower working memory performance, perceptual reasoning, and inhibition, and that higher instances of cannabis use lead to impairment in delayed recall memory. The alcohol model showed that alcohol use over the 5 years was linked to lower spatial working memory performance, perceptual reasoning, and trouble exhibiting inhibitory control.
Combined, alcohol and cannabis showed that alcohol negatively impacted perceptual reasoning, and that cannabis use lead to lower performance on multiple tasks dealing with control and memory, independent to alcohol use.
This study suggests that cannabis use frequency is linked to reduction in delayed recall memory and lack of perceptual reasoning. These results, along with existing data on neuroplasticity of cannabis users, imply that adolescent cannabis use is related to more long-term consequences on cognitive functions than alcohol.
This study was unique in its robust data collected multiple times over 5 years. The results lead to potential for more research in cohorts of adolescents as well as those entering young adulthood, when drug and alcohol use becomes more prevalent.
Take Away: Adolescent cannabis use negatively impacts important cognitive functions such as memory and reasoning, and these effects are more pronounced than those seen with adolescent alcohol use.
Morin, J.G., Afzali, M.H, Bourque, J., et al. (2018). A Population-Based Analysis of the Relationship Between Substane Use and Adolescent Cognitive Development. The American Journal of Psychiatry. doi.org/10.1176/appi.ajp.2018.18020202