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Casual Marijuana Use Linked to Changes in Brain

The brain regions are tied to motivation, emotion and reward, researchers say

WebMD News from HealthDay

By Dennis Thompson

HealthDay Reporter

TUESDAY, April 15, 2014 (HealthDay News) -- Young people who occasionally smoke marijuana may be rewiring their brains, with their pot use causing structural changes to brain regions related to motivation, emotion and reward, a small study says.

Recreational pot use by a small group of young adults caused significant changes to the shape and density of both the nucleus accumbens, a region of the brain involved in reward and addiction, and the amygdala, which helps process emotion and form long-term memories, the study authors reported.

These changes show that pot users' brains adapt to even low-level marijuana exposure, potentially making a person more vulnerable to drug addiction or changing their thought processes and emotions in unknown ways, the researchers said.

"These are two brain regions you do not want to mess around with," said study senior author Dr. Hans Breiter, a professor of psychiatry and behavioral science at Northwestern University Feinberg School of Medicine. "All parts of the brain are important, but some, like these, are more fundamental. It raises a very serious issue, given that we saw these changes in casual marijuana users."

Previous research had revealed similar changes in brain structure among heavy marijuana users. But this is the first study to show that even casual use of the drug can alter a person's brain, said study lead author Jodi Gilman, a researcher with the Massachusetts General Hospital Center for Addiction Medicine.

"We were interested in looking at these young adults who aren't addicted," Gilman said. "They aren't reporting any problems from marijuana, and yet we still see these brain changes."

These findings could take on significance as more and more states consider legalizing marijuana, following the example already set by voters in Colorado and Washington.

"The earlier the onset of marijuana use in a kid, the worse potential implications you could be seeing," Breiter said.

Added Gilman: "We just don't know how much is safe. It's not harmless. We don't know the harm, but it's not free from harm."

Paul Armentano, deputy director of the pro-marijuana advocacy group NORML, said such findings also could be used to make the case that marijuana should be legalized and tightly regulated.

He noted that studies also have found adverse health consequences associated with use of alcohol, tobacco and prescription drugs.

"It's precisely because of these consequences that these products are legally regulated, and their use is restricted to particular consumers and specific settings," Armentano said.

"A pragmatic regulatory framework that allows for the legal, licensed commercial production and retail adult sale of marijuana but restricts its use among young people -- coupled with a legal environment that fosters open, honest dialogue between parents and children about cannabis' potential harms -- best reduces the risks associated with the plant's consumption or abuse," Armentano added.

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