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Casual Marijuana Use Changes Brain Structure, New Study Finds

As legal marijuana, both medicinal and recreational, starts to gain acceptance across the country, it’s not surprising that scientists are putting the microscope to the effects of cannabis use. A new study on casual marijuana use found some disappointing results for the optimistic pot supporter: casual use of marijuana causes distinct abnormalities in the brain.

Researchers at Northwestern University were inspired to examine the effects of cannabis on the brain in young adults who use it once or twice a week. Dr. Hans Breiter, the study’s co-senior author, said that his lab had previously linked heavy pot use to changes in the brain that resembled those of patients with schizophrenia. He and his team wanted to see if there were also abnormalities with less frequent use.

The study, to be published today in the Journal of Neuroscience, found structural changes in two main centers of the brain: those responsible for working memory and motivation.

“There were abnormalities in their working memory, which is fundamental to everything you do,” Breiter told “When you make judgments or decisions, plan things, do mathematics – anything you do always involves working memory.  It’s one of the core fundamental aspects of our brains that we use every day.  So given those findings, we decided we need to look at casual, recreational use.”

The MRIs also revealed that the brain regions responsible for emotions, decision making, and motivation—the nucleus accumbens and the amygdala— were affected in density, volume, and shape in casual marijuana users.

Breiter sees a need for further investigation of marijuana’s effects on patients over time.

“My worry is we haven’t studied this compound and here we are looking to change legislation on it,” Breiter said.

The Northwestern research, however, is just the beginning. The team analyzed 20 users between the ages of 18 and 25, compared to 20 controls subjects— a small pool.

“This study is just a beginning pilot study, but at the same time, the results that came out are the same as a canary in a coal mine,” Breiter said.  “...The interaction of marijuana with brain development could be a significant problem.”



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