UC San Diego study finds teen cannabis initiation linked to restricted memory and cognitive growth

A UC San Diego study of 11,000 teens shows that starting cannabis is linked to restricted gains in memory and focus during critical brain development years.

By: AXL Media

Published: Apr 20, 2026, 8:15 AM EDT

Source: Information for this report was sourced from UC San Diego Health Sciences

Stalled Cognitive Gains During a Critical Window of Development

The transition from early adolescence into young adulthood is characterized by a rapid expansion of cognitive capabilities, yet new research suggests that cannabis use may blunt this growth. According to a study led by the University of California San Diego, teenagers who started using cannabis failed to improve their thinking and memory skills at the same rate as those who abstained. Researchers monitored 11,036 participants starting from ages 9 and 10, following them until they reached ages 16 and 17. The data showed that while many of these youth performed at or above average levels before initiation, their cognitive progress leveled off once cannabis use began, while their non-using peers continued to show developmental gains.

Leveraging Biological Testing to Validate Substance Exposure

To ensure the accuracy of the findings, the research team went beyond traditional self-reporting methods, which can often be unreliable in adolescent populations. By combining participant surveys with biological testing of hair, urine, and saliva samples, the scientists were able to detect drug exposure ranging from recent use to several months prior. This multi-modal approach allowed for a more precise categorization of users and non-users. Dr. Natasha Wade, lead author and assistant professor at the UC San Diego School of Medicine, noted that these objective measures were essential for identifying how the presence of specific cannabinoids correlates with long-term neurocognitive trajectories across the large-scale cohort.

Identifying THC as a Primary Driver of Memory Deficits

The study provided a granular look at the components of cannabis, specifically distinguishing between the effects of tetrahydrocannabinol (THC) and cannabidiol (CBD). In a subset of participants, those with verified THC exposure exhibited significantly worse episodic memory over time than their peers. In contrast, those with evidence of CBD exposure did not show the same pattern of cognitive restriction, though researchers cautioned that the CBD sample size was relatively small. These results implicate THC, the primary intoxicating ingredient in cannabis, as the likely driver behind the observed neurocognitive changes, highlighting the risks of products that may contain higher concentrations of the compound than advertised....