A new study finds teen marijuana use may slow brain development in key areas like thinking and memory.Researchers followed more than 11,000 children starting at ages 9 or 10 through their mid-to-late teens.They tracked their substance use through self-reports as well as hair, urine, and saliva tests, and over time, assessed memory, attention, language, and processing speed.The results: kids who started using pot as teens showed slower gains across all of these skills. While some performed just as well – or even better –than their peers when they were younger, their progress leveled off when they began using.THC was linked to worse memory over time, while CBD wasn’t—suggesting THC may be driving the changes.The lead researcher says “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.” While the differences were modest, she says they can affect school performance and daily life. The team will continue tracking participants into young adulthood to study long-term effects.Source: NeuropsychopharmacologyAuthor Affiliations: University of California, San Diego, The University of Sydney, University of Wisconsin, Huestis & Smith Toxicology, LLC, Columbia University .Sign up for our weekly HealthDay newsletter