New research from UC San Diego is shedding light on the potential impact of adolescent cannabis use on cognitive development. The study, which analysed data from the long-term Adolescent Brain Cognitive Development (ABCD) Study, suggests that frequent cannabis use during adolescence may be associated with slower cognitive growth in several key areas.
Understanding Adolescent Cannabis Use and Brain Development
The Adolescent Brain Cognitive Development (ABCD) Study is a comprehensive, long-term project that commenced in 2016, involving over 11,000 children across the United States. It represents the largest study of child health and brain development in the country. Researchers at UC San Diego analysed the initial seven years of data from this extensive project to explore how cannabis might influence the developing brain.
According to the Centers for Disease Control and Prevention, cannabis use remains prevalent among teenagers, with approximately one-third of 12th graders reporting use in 2022. The agency has previously indicated that using cannabis during adolescence could have lasting effects on brain development, particularly with frequent use.
Key Cognitive Findings
Dr. Natasha Wade, an assistant professor of psychiatry at the UCSD School of Medicine, led the research team. Their findings, published in April, indicated that adolescents who used cannabis did not exhibit the same rate of cognitive growth as their non-using peers. Specifically, the study found:
- Verbal memory was observed to be affected, with test scores showing no improvement over time in cannabis users.
- Cannabis use appeared to inhibit the growth of learning, memory, and visual-spatial skills.
- Limitations were also observed in attention span and processing speed.
Dr. Wade noted that some of these results showed effect sizes considered substantial by typical statistical standards, suggesting a more consistent and stronger impact than initially anticipated by the research team.
Methodology: Hair-Based Testing
A unique aspect of this study was its approach to identifying cannabis use. Researchers combined self-report data with toxicological testing, specifically using hair samples. This method offers a longer detection window of up to three months for frequent cannabis use, compared to the 30-day window typically associated with urine tests. This extended timeframe allowed for a more accurate assessment of consistent use patterns among participants.
The hair tests focused on detecting carboxy-THC, a metabolite of THC that indicates personal ingestion rather than external contamination from smoke. This allowed researchers to identify cannabis use regardless of the consumption method, including edibles and vapes. The findings primarily relate to THC, as CBD is more challenging to detect due to the absence of a clear metabolite. The study observed the strongest correlation between frequent cannabis use, as identified by hair testing, and reduced long-term memory.
Nuances and Research Considerations
It is important to note that this was an observational study, meaning researchers cannot definitively state that cannabis directly causes these cognitive restrictions. Other potential contributing factors, such as family history of substance use disorders, prenatal exposure, and mental health conditions, were controlled for within the study’s modelling. Dr. Wade emphasised that despite these controls, a relationship between adolescent cannabis use and cognitive development was observed, indicating a potential risk for teenagers during a critical period of brain change.
Other experts have also weighed in on the study’s implications and limitations:
- Devan Kansagara, a professor and physician at Oregon Health and Science University, acknowledged the study’s approach but raised concerns that analysing cognitive differences between users and non-users might oversimplify the complex reality of ongoing and varying levels of use. He noted that while hair testing identified more frequent users, some key cognitive impacts were not consistently replicated in that specific subgroup analysis, though the link to declining memory aligned with existing research.
- Robert Welch, director of the National Center for Cannabis Research and Education at the University of Mississippi, highlighted the study’s large sample size as a strength. However, he suggested that the “user vs. non-user” approach simplifies a more complex reality. Welch stated, “It really needs to be highlighted more in terms of the potency of the cannabis and the frequency of use. It’s very difficult to pinpoint exactly what kind of products these consumers are using. It’s such a complex plant and the products that are produced from the plant are all so different.” He also noted that national comparisons are complicated by differences in state laws, particularly for cannabis, as states with recreational laws like California may offer access to higher quality, regulated products compared to unregulated products found elsewhere. As researchers continue tracking participants into adulthood, future data may clarify how lasting these cognitive differences are and whether they persist after cannabis use stops.
Disclaimer: This article is for informational purposes only and does not constitute medical advice. Hemp Gazette does not provide medical recommendations, diagnoses, or treatment plans. Always consult a qualified healthcare practitioner before making any decisions regarding your health or any medical condition. Statements concerning the therapeutic uses of hemp, cannabis, or cannabinoid-derived products have not been evaluated by Australia’s Therapeutic Goods Administration (TGA). Medicinal cannabis products in Australia are accessed via prescription pathways under TGA regulation.
