Daily marijuana use has a measurable effect on the brain, a new study finds. Photo by Dean J. Koepfler/Tacoma News Tribune/MCT via Getty Images.

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.

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Correction: The title of this post was corrected to indicate that researchers have not concluded a direct link between heavy marijuana use and abnormal brain structure or poor memory, but to reflect that the study shows a possible association between the two.