Cannabis use in adolescence linked to cognitive deficits

In recent years, the conversation around cannabis use has shifted dramatically, with an increasing number of countries and states re-evaluating its legal status.

Amidst this evolving landscape, a study led by Natasha E. Wade, an assistant professor at the University of California at San Diego and head of the Neuro D-Tox Lab, sheds new light on the potential impacts of cannabis use on adolescents. 

Based on data from the Adolescent Brain Cognitive Development (ABCD) Study, the research presents compelling evidence that even light to moderate cannabis use during early adolescence can lead to cognitive deficits, especially in memory and attention.

The developing brain

Cannabis contains the psychoactive compound tetrahydrocannabinol (THC), which has led to its widespread use both medicinally and recreationally. However, there are growing concerns about its use among adolescents – whose brains are still undergoing critical developmental phases. 

The potency of cannabis and the methods of its use have changed significantly over the years, prompting a deeper investigation into its effects on the developing brain. The research team aimed to address the challenges in accurately identifying adolescent cannabis users. 

Accurate group categorization 

“Cannabis use in adolescents is not uncommon, though it is unclear if younger teens are comfortable disclosing their use,” said Professor Wade. “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.”

How the research was conducted 

The researchers focused on a subset of participants in the ABCD study. They analyzed 2,971 hair samples from the fourth-year follow-up when the participants were around 13-14 years old. 

The experts looked for THC, THCCOOH (an inactive metabolite indicating personal use), and cannabidiol (CBD), aiming to objectively measure cannabis exposure.

Critical new insights

The researchers found significant cognitive differences between adolescents who used cannabis and those who did not. Specifically, cannabis users exhibited poorer performance in episodic memory tasks, which involve recalling specific events or experiences, and showed marginal deficits in receptive language skills, crucial for understanding words and sentences. 

Furthermore, higher concentrations of THCCOOH were associated with lower scores in receptive language and attention tasks, underscoring the potential for cannabis to impact key cognitive functions during a critical period of brain development.

The findings emphasize the importance of using objective measures in research to uncover more accurate relationships between brain behavior and substance use. 

Broader implications 

“When we carefully determine cannabis use group status in teens 13-14 years-old and match those with cannabis use to socio-demographically 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,” Professor 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.”

The study not only provides valuable insights into the cognitive effects of adolescent cannabis use but also sets the stage for future research. Professor Wade and her team plan to leverage the ABCD study’s longitudinal data to explore cognitive changes over time in relation to cannabis use, as well as to investigate patterns of substance use initiation and escalation in teens.

The study is published in the journal Addictive Behaviors. 

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