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Marijuana's Bad Effects on the Brain
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Marijuana's Bad Effects on the Brain


The news about marijuana over the last several months has been largely positive. Its value in reducing nausea from cancer treatment has improved its image. In late 2012, Colorado and Washington were the first states to legalize the sale and cultivation of marijuana.

Articles about the beneficial effects of marijuana, including its ability to ease neuropathic pain, have been in the news. CNN’s chief medical correspondent, Dr. Sanjay Gupta, embraced the beneficial effects of medical marijuana publicly.

Not all researchers and clinicians, however, are convinced that marijuana is good for you. It can cause memory problems and bouts of anxiety.

Even casual marijuana users exhibited significant abnormalities in the shape, size and density of brain regions compared to subjects who had never smoked marijuana at all.

These symptoms may be related to the findings of a recent study which found that even a small amount of marijuana use can cause large structural changes in the brain.

The study, by scientists at Northwestern University and Harvard’s Massachusetts General Hospital, looked at the brains of 40 young adults from Boston, aged 18 to 25, who smoked marijuana casually — not more than once a week. All were found to be moderate users with no history of substance abuse.

The scientists used magnetic resonance imaging (MRI) to compare the size, shape, and density of two brain regions: the nucleus accumbens and the amygdala. Both of these regions are involved in the brain’s reward pathway, which is activated during drug — and food — consumption.

To their surprise, the researchers found that even casual marijuana users exhibited significant abnormalities in the shape, size and density of brain regions compared to subjects who had never smoked marijuana at all.

Marijuana users had a big increase in the size of their nucleus accumbens, and this directly correlated with how much marijuana a person reported smoking. In other words, the more pot a person reported smoking, the larger their nucleus accumbens.

The increased size and density of the nucleus accumbens in casual marijuana users, the researchers believe, is evidence that the brain is forming new connections that could encourage further drug use. New brain connections are also seen in rodents that are administered THC, the active ingredient in marijuana.

“This study raises a strong challenge to the idea that casual marijuana use isn't associated with bad consequences,” said Hans Breiter, one of the authors of the study and a professor in Psychiatry and Behavioral Sciences at Northwestern University School of Medicine in a statement.

The study is published in the Journal of Neuroscience.

April 22, 2014


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