Powerful New Pot May Harm the Brain

Powerful New Pot May Harm the Brain But marijuana advocate calls the study 'speculative'
WebMD News from HealthDay

By Dennis Thompson

HealthDay Reporter

WEDNESDAY, Dec. 2, 2015 (HealthDay News) -- Smoking high-potency marijuana might damage nerve fibers that connect the brain's two hemispheres, a new study reports.

MRI scans of nearly 100 people -- including some diagnosed with psychosis -- associated frequent use of high-potency "skunk" marijuana with damage to the corpus callosum, the largest white matter structure in the brain.

"We found that frequent use of high-potency cannabis significantly affects the structure of white matter fibers in the brain, whether you have psychosis or not," said senior researcher Dr. Paola Dazzan, of the Institute of Psychiatry, Psychology & Neuroscience at King's College London.

Further, her team said the damage appears to be dose-dependent. "This reflects a sliding scale where the more cannabis you smoke and the higher the potency, the worse the damage will be," Dazzan said in a college news release.

This is vital information, given that the potency of street marijuana has increased over the last decade, the study authors said.

Reactions to the findings in the United States were mixed, however.

Dr. Scott Krakower, assistant unit chief of psychiatry at Zucker Hillside Hospital in Glen Oaks, N.Y., agreed that the study "supports the idea that using high-potency marijuana can be detrimental."

The upshot? "People should be aware that using this agent isn't benign, and that there are changes to the brain," he said.

But marijuana advocates said the study had limitations.

The damage observed by the researchers appears to be very minor, amounting to a "2 percent change in the corpus callosum" structure, said Mitch Earleywine, chair of NORML, a group that promotes marijuana legalization.

Earleywine, who is also a professor of psychology at the State University of New York, Albany, added that the researchers did not measure the study participants' memory or brain function. "So we have no idea if this had any impact on anything that matters, like memory or impulsivity or depressive symptoms," he said.

For this study, researchers used MRI to examine white matter in the brains of 56 patients who had been diagnosed with psychosis, as well as 43 healthy people from South East London.

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