Is adolescent cannabis use affecting young minds more than we thought? A recent study published in the journal Addictive Behaviors reveals significant insights into how cannabis consumption among teenagers could impact their cognitive development, particularly in areas related to memory and attention. The research suggests that even light to moderate cannabis use in early adolescence is associated with cognitive deficits.
Cannabis, often known as marijuana, has been at the center of an evolving conversation, especially as various countries and states have begun to change its legal status. Known for its psychoactive properties primarily due to the compound tetrahydrocannabinol (THC), cannabis has been increasingly used for both medicinal and recreational purposes.
Despite its growing acceptance, concerns have persisted about its impact on adolescent users, whose brains are still in a critical developmental stage. This concern, coupled with the observation that cannabis potency and the methods of its use have significantly changed over recent decades, prompted researchers to conduct a comprehensive study aimed at understanding the substance’s effects on young users more clearly.
“Cannabis use in adolescents is not uncommon, though it is unclear if younger teens are comfortable disclosing their use,” said study author Natasha E. Wade, an assistant professor at the University of California at San Diego and head of the Neuro D-Tox Lab. “We wanted to improve our methods for identifying those who have used cannabis by both asking teens if they had use and by using objective, toxicological testing through hair samples. Having more accurate group categorization may improve our ability to determine cognitive correlates of cannabis use — which we also assessed here.”
The study leveraged data from the Adolescent Brain Cognitive Development (ABCD) Study, a large-scale, longitudinal research effort tracking nearly 12,000 youth across the United States from the age of 9-10 years into late adolescence. Researchers focused on a subset of participants from whom hair samples were collected during the fourth year of the study, when the participants were around 13-14 years old.
Hair samples were analyzed for THC, THCCOOH (an inactive metabolite of THC that indicates personal use rather than exposure to smoke), and cannabidiol (CBD). This method provided an objective measure of cannabis exposure, which was then correlated with self-reported cannabis use and cognitive performance assessed through the NIH Toolbox—a collection of neurocognitive tests.
Out of the 2,971 hair samples analyzed, 601 were from the Year 4 follow-up, and 123 of these were identified as belonging to youth who reported using cannabis or had cannabinoids detected in their hair. These participants were compared with 123 matched controls who did not report cannabis use and had no cannabinoids detected in their hair. The matching process ensured that both groups were comparable in terms of age, sex, race/ethnicity, and socioeconomic status, thus isolating cannabis use as the variable of interest.
The researchers found that adolescents who used cannabis showed notably poorer performance on tasks measuring episodic memory, the ability to recall specific events or experiences from one’s past, and marginal deficits in receptive language skills, which involve understanding words and sentences.
Moreover, higher concentrations of THCCOOH in the hair were linked to lower scores in both receptive language and attention tasks. These associations suggest that the impact of cannabis on young brains might be more pronounced than previously understood, affecting key cognitive functions that are critical during the developmental stage of adolescence.
“When we carefully determine cannabis use group status in teens 13-14 years-old and match those with cannabis use to sociodemographically matched controls, we do see that there are group differences in memory, and that more cannabis use was associated with poor verbal abilities, inhibition, working memory, and episodic memory,” Wade told PsyPost.
“We also found that combining hair toxicology with self-report data shows more brain-behavior relationships than self-report data alone. This indicates that within substance use research and in other domains, too, we need to use more objective measurement to improve our ability to accurately investigate important research questions.”
However, the study is not without its limitations. Not all participants could provide hair samples due to various reasons, such as hairstyles that could be disrupted by sampling or unwillingness to participate in this aspect of the study. Financial constraints also limited the number of hair analyses that could be conducted, potentially affecting the sample size and the study’s generalizability. Furthermore, the cross-sectional nature of this analysis means that it captures a snapshot in time, making it challenging to determine causality or the direction of the relationships observed.
“Our analyses were all cross-sectional, so causation cannot be inferred,” Wade explained. “While we do have longitudinal data from this cohort, we could not use the same grouping process (of combining self-reported substance use history with toxicology results) to determine whether youth had used cannabis at prior time points, and so we could not run analyses longitudinally. It is interesting to note, though, that when participants were initially enrolled in the study at 9-10 years-old, there were no significant differences between groups in cognitive performance.”
Looking ahead, the researchers plan to use more data from the ABCD study to investigate cognitive changes over time in relation to cannabis use.
“With this longitudinal data, we hope to expand our use of objective measures to carefully investigate patterns of substance use initiation and escalation in teens and how that impacts their development, brain health, mental health, and physical health,” Wade said. “We are also running smaller, more detailed projects to similarly investigate risk and resilience factors of substance use during adolescence and young adulthood.”
The study, “Cannabis use and neurocognitive performance at 13–14 Years-Old: Optimizing assessment with hair toxicology in the Adolescent brain cognitive development (ABCD) study“, was authored by Natasha E. Wade, Alexander L. Wallace, Marilyn A. Huestis, Krista M. Lisdahl, Ryan M. Sullivan, and Susan F. Tapert.