Study: Smoking Marijuana Makes Part of the Brain Smaller

With even more people smoking marijuana, there has been an uptick in scientific research about the effect the drug has on a user's mind and body. One such study took a longer-term look at what chronic pot smoking does to the brain and found it actually shrunk part of it.

The research from the University of Texas, Dallas published in the Proceedings of the National Academy of Sciences this week was the first to describe the impact long-term marijuana use had on brain function and structure.

“We have seen a steady increase in the incidence of marijuana use since 2007," Dr. Francesca Filbey, director of the Cognitive Neuroscience Research in Addictive Disorders at the Center for BrainHealth, said in a statement. “However, research on its long-term effects remains scarce despite the changes in legislation surrounding marijuana and the continuing conversation surrounding this relevant public health topic.”

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The study compared 48 people who used marijuana an average of three times a day and 62 non-users. The researchers found a lower IQ in those who smoked the drug as well as a smaller orbitofrontal cortex, a part of the brain associated with addiction and decision making.

They did see more brain connectivity in those who smoked weed, but it wasn't necessarily a positive thing.

“The results suggest increases in connectivity, both structural and functional that may be compensating for gray matter losses. Eventually, however, the structural connectivity or ‘wiring’ of the brain starts degrading with prolonged marijuana use," Dr. Sina Aslan, founder and president of the company Advance MRI and a professor at the university, said.

This increased connectivity for a short period of time might be why smokers "seem to be doing fine," while another part of their brain was reduced, Filbey said.

Filbey acknowledged that this study doesn't "conclusively address whether any or all of the brain changes are a direct consequence of marijuana use," but she said "these effects do suggest that these changes are related to age of onset and duration of use.”

Watch this report about the study:

She added to the Washington Post that the marijuana smokers in the study might be considered unusually heavy users, but that helped scientists find structural differences in the brain.

The researchers analyzed the brains of study participants using MRI and controlled for other substance use like alcohol and tobacco smoking so it would limit any influence on their findings.