A sweeping new analysis from UC San Diego researchers is raising fresh concerns for parents of young teens, suggesting that kids who start using marijuana early show smaller gains in memory, attention and thinking speed between late childhood and mid‑adolescence. Tracking more than 11,000 U.S. children from roughly ages 9–10 into their mid‑teens, the team found that cognitive improvements in cannabis‑using youths often flattened while their non‑using peers kept moving upward. The authors stress that the findings show associations, not proof that cannabis directly causes slower development.
The results appear in Neuropsychopharmacology, where investigators describe using longitudinal mixed‑effects models on 11,036 participants from the Adolescent Brain Cognitive Development (ABCD) cohort. They adjusted for sociodemographic factors, family histories of substance use, prenatal exposures, early mental‑health symptoms and other substance use, then compared how neurocognitive performance changed over time. To sharpen the picture of who had actually used cannabis recently, they combined self‑reports with toxicology from hair, urine and oral fluid samples.
What The Paper Found
Across tests of immediate and delayed memory, attention, language and processing speed, teens who initiated cannabis use showed more limited development than those who did not. In a smaller subgroup that underwent repeat hair testing, participants with detectable THC exposure had worse episodic memory trajectories, while those with CBD exposure did not show the same pattern. "These results point to THC as a likely driver of the changes we're seeing," lead author Natasha Wade told Medical Xpress.
How Researchers Measured Use
The analysis drew on the ABCD Study, a 21‑site, NIH‑funded project that enrolled nearly 12,000 children at ages 9–10 and has been following them into young adulthood. That design gives scientists the statistical power to model changes within each participant over time and to account for differences among research sites. By pairing detailed timeline follow-back interviews with biospecimen testing, the UCSD‑led team aimed to cut down on errors that can come from self‑report alone and to explore whether specific cannabinoids track with different cognitive outcomes. The authors argue that these methods make it more likely that the observed trajectory gaps relate to substance exposure patterns rather than simple measurement noise.
What It Means For San Diego Families
For families in San Diego, the findings add another caution flag around teen cannabis use at a time when products are more potent and easier to find. Local coverage by FOX 5 San Diego highlighted UCSD's recommendation that delaying cannabis use is one way to support healthy brain development while researchers continue to track this large group of kids. Parents and schools are likely to keep a close eye on future updates as scientists tease apart how age of first use, frequency and product type shape outcomes.
Next Steps
The research team plans to follow participants into young adulthood to see whether these early cognitive differences persist, worsen or fade over time, according to Neuropsychopharmacology. They underline that the work does not prove causation and that environmental influences, personality traits or other unmeasured factors could still play a role despite the extensive controls. Until clearer answers emerge, Wade and colleagues are leaning on prevention messages and accurate cannabis product labeling as key pieces of the public‑health response to rising youth access.
