Marijuana use during middle to late adolescence may be associated with changes in brain development, a new study suggests.

The changes may adversely affect reasoning, decision-making and memory skills as teens age, HealthDay reports.

The study included 799 participants who had brain scans at age 14 and again at 19. The researchers found those who started using marijuana tended to have increased thinning in the cerebral cortex, the area of the brain responsible for language, thought and perception. The more marijuana teens used, the more significant the thinning. The regions of the brain most affected were those associated with working memory, inhibition, attention and emotional regulation.

Lead researcher Matthew Albaugh of the University of Vermont Medical Center said by age 19, teens who used marijuana showed signs of being unable to stay focused without distraction. He said the researchers plan to continue to study the teens to age 23.