Lifestyle

Study: Teen Cannabis Use Is Slowing Brain Development

By Erica Coleman · May 5, 2026

The largest study of adolescent brain development ever conducted in the United States has produced a finding that parents in states where cannabis is legal need to understand — and the edibles problem is why many of them don’t see it coming.

Researchers at UC San Diego published a study on April 20 in the journal Neuropsychopharmacology analyzing data from 11,036 participants in the Adolescent Brain Cognitive Development Study — a 21-site, federally funded project that has been tracking children from ages 9 and 10 through mid-adolescence. The finding: teenagers who begin using cannabis show measurably slower gains in memory, attention, language, and processing speed compared to their non-using peers. Their brains keep developing — but at a slower rate.

“Adolescence is a critical time for brain development, and what we’re seeing is that teens who start using cannabis aren’t improving at the same rate as their peers,” said lead author Natasha Wade, PhD, assistant professor of psychiatry at UC San Diego School of Medicine. “These differences may seem small at first, but they can add up in ways that affect learning, memory and everyday functioning.”

The study is correlational — it shows an association between teen cannabis use and slower cognitive gains, not proof that cannabis directly causes the effect. The researchers controlled for sociodemographic factors, family history of substance use, prenatal exposures, and early mental health symptoms. The association held.

None of that is the most alarming part of the picture for parents.

The most alarming part is how teenagers are accessing cannabis in 2026 — and how invisible that access has become. In March 2025, eleven students at William Floyd Middle School on Long Island were hospitalized after a classmate distributed THC gummies that looked like ordinary candy. Ages 12 and 13. Dizziness, racing heart rates, vomiting. None of them recognized what they had consumed.

The incident was not isolated. It was part of a documented national pattern: cannabis-involved emergency department visits among children and adolescents under 15 surged during the pandemic years and have not come back down. North Carolina alone recorded more than 1,400 ER visits for cannabis consumption among people under 24 in 2025. Emergency physicians are now treating what they describe as Cannabinoid Hyperemesis Syndrome in young patients on a weekly basis.

The mechanism driving this is the edibles market. Cannabis-infused gummies, chocolates, beverages, and baked goods are packaged in ways that often deliberately mimic familiar candy and snack brands. A THC gummy looks like a Sour Patch Kid. A cannabis chocolate bar looks like a Hershey bar. The branding difference is often a small leaf logo and packaging text that is easy to miss — especially for a teenager who found it in a parent’s nightstand drawer or received it from a classmate.

The parent who would never allow their teenager to smoke marijuana may have cannabis gummies sitting in their medicine cabinet for anxiety or sleep, with no meaningful conversation having taken place about what those products are or where they are stored. The CDC has specifically warned that children who consume THC can become very sick — with problems walking or sitting up, difficulty breathing, and symptoms severe enough to require emergency care.

The UC San Diego study’s message is about long-term cognitive development. The edibles crisis is about acute poisoning happening right now. Both are real. Both are connected to the same underlying shift: cannabis legalization has made a potent psychoactive substance more available, more normalized, and more invisible than it has ever been — while the brains most vulnerable to its effects are still forming.

The researchers noted the study did not determine whether the cognitive effects are permanent or reversible through abstinence. That work continues. What the study does establish — with more statistical power than any previous research — is that the concern parents have had is not paranoia. It is supported by the largest dataset on adolescent brain development the United States has ever assembled.