The study, published in the journal Neuropsychopharmacology, followed 11,036 children from ages nine and 10 through to ages 16 and 17. Researchers found that regular cannabis use restricted vital growth in memory, attention, language and processing speeds over time. THC, the psychoactive ingredient in marijuana, was linked to worse memory in teens compared to CBD, and may lead to shrinkage of the hippocampus and changes in white matter. The deficits were small, but could affect school performance and daily life, the researchers said.
Lead study author Dr Natasha Wade said: "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." She added: "These differences may seem small at first, but they can add up in ways that affect learning, memory and everyday functioning."
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.
About 18 million Americans report using marijuana daily or nearly every day, a 15-fold increase from 1992 to 2022. About one in seven marijuana users are teenagers. Marijuana is fully legal in 29 US states and fully illegal in four states. The exact magnitude of cognitive deficits observed in the study has not been specified, and the definition of 'regular cannabis use' used in the research remains unclear.
These differences may seem small at first, but they can add up in ways that affect learning, memory and everyday functioning.