Marijuana Use Can Change Brain's Physical Structure

Sustained, daily marijuana use was enough to physically change the structures of teenagers’ brains, affecting working memory, academic performance, and everyday function.

Matthew Smith, a research professor in psychiatry and behavioral sciences at Northwestern University Feinberg School of Medicine, and colleagues, conducted a study of 97 participants including healthy controls, those with history of at least 3 years of sustained marijuana use who had also been marijuana-free for at least 2 years, and participants with schizophrenia.

Those who smoked marijuana had begun between ages 16 and 17 years, and were now in their early 20’s.

Researchers used structural MRI to map irregularities in participants’ brains, finding that “Memory-related structures in their brains appeared to shrink and collapse inward, possibly reflecting a decrease in neurons.“

Brain abnormalities related to marijuana use also appeared similar to those found in schizophrenia, and brain changes appeared more abnormal in those that began using the drug at earlier ages.

“The study links the chronic use of marijuana to these concerning brain abnormalities that appear to last for at least a few years after people stop using it,” researchers concluded.

“With the movement to decriminalize marijuana, we need more research to understand its effect on the brain.”

The full study was published in Schizophrenia Bulletin.

–Michael Potts


1. Smith MJ, Cobia DJ, Wang L, Alpert KI, et al. Cannabis-Related Working Memory Deficits and Associated Subcortical Morphological Differences in Healthy Individuals and Schizophrenia Subjects [published online ahead of print December 15, 2013]

2. Marijuana Users Have Abnormal Brain Structure and Poor Memory [press release]. Chicago, IL. Northwestern University.