Study Finds That Smoking Pot Has No Effect on Brain Volume

By McCarton Ackerman 08/31/15

But weed can still cause structural damage to the brain.

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In the latest study to analyze the effects of marijuana on the brain, new findings show that while marijuana does cause certain structural changes in the brain, it has no effect on overall brain volume.

The report, published in the latest issue of JAMA Psychiatry, looked at a group of siblings ages 22 to 35, comprised of 483 people in total. Among them, 262 reported using marijuana at least once. The participants were broken into three groups: siblings who had used marijuana before, siblings who never had, and those where only one sibling had tried it.

Although those who reported using marijuana had smaller amounts of volume in certain parts of the brain like the left amygdala, the differences between their brains and the ones of those who had never smoked still fell within a range considered to be normal. The authors concluded that there was “no evidence” to suggest pot exposure affected brain volume and said other circumstances could have sparked these changes.

“Any relationship that we did see between cannabis use and brain volumes was due to predisposing factors that influence both cannabis use and brain volumes,” said study author Arpana Agrawal, an associate professor at Washington University School of Medicine.

The researchers will now look to examine whether marijuana does in fact potentially have harmful effects on the brain or whether the risks are greater in specific groups of people. They will examine whether brain volume has any effect on whether or not a person uses marijuana.

These results were far less morbid than a December 2013 study conducted by the Northwestern University Feinberg School of Medicine in Chicago, which concluded that chronic marijuana use by teenagers can ultimately lead to long-term brain damage.

The findings, published in the journal Schizophrenia Bulletin, showed that heavy pot smoking affected teen brains in the sub-cortical regions; primitive structures that are part of memory and reasoning circuits.

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McCarton Ackerman is a freelance writer and editor living in Portland, Oregon. He has been a contributor for The Fix since October 2011, writing on a wide range of topics ranging from medical marijuana in Colorado to the world's sexiest drug smugglers. Follow him on Linkedin and Twitter.