Teenagers who smoked marijuana daily for three years performed poorly on memory tasks and showed abnormal changes in brain structure, according to a Northwestern Medicine study. Researchers in Chicago observed the brains of teenagers who were heavy users of marijuana. In those individuals, memory-related structures in the brain appeared to shrink and collapse inward, possibly indicating a decrease in neurons.

These abnormalities were recorded two years after the teens stopped using marijuana, possibly indicating long-term effects, and look similar to schizophrenia-related brain abnormalities.

The brains were shaped more abnormally for individuals who began marijuana use at a younger age, according to the reports, which suggest that memory regions of the brain are more susceptible to the drug at earlier ages.

The research was published in the December issue of Schizophrenia Bulletin.