Study Links Casual Pot Use With Brain Abnormalities

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Young adults who smoke marijuana at least once a week showed changes in the size and shape of two key brain regions, according to a new study of 20 pot smokers and 20 non-pot smokers between 18 and 25.

This is the first time recreational marijuana use has been connected to significant brain changes.

The findings, a collaboration between Northwestern University and Massachusetts General Hospital/Harvard Medical School, were published in The Journal of Neuroscience.

The senior author of the study, Hans Breiter, joins Here & Now's Robin Young to discuss the research.

Interview Highlights: Hans Breiter

On the findings of the study

"Basically we looked in at two critical structures for reward processing and judgement decision making and also the processing of emotion. And we found that these two structures were abnormal in these casual users compared to well-matched healthy controls."

On the reward processing part of the brain

"A fundamental aspect of addiction research has been this concept of reward and that substances of abuse basically kind of hijack this system and substitute for things that are naturally rewarding such as food or playing with your kids or taking a moment to read a piece of Proust or something. Since early work in the '90s, we found that the nucleus accumbens is basically one of many many regions of the brain that process what is positive and negative for a person and facilitates making judgments and decisions based on these assessments of what's positive and negative."

On the small sample size and self-reporting of pot use

"This is an excellent question and it's a question that gets raised in any type of study where you take a sample of society and then try to extrapolate out from it. We used statistics that allow for random effects analysis. We looked at the data in multiple ways. I myself am known as a bit of a conservative neuro-imager and don't publish things unless I believe it's going to be replicated. But it gets to this issue, how can you extrapolate from 40 people to the rest of society — you can't. This is a pilot study, absolutely needs to be verified with larger cohorts and in cohorts around the country. There's no way with just 40 people that you can sample the diversity of a country with as much diversity as we have."


  • Hans Breiter, professor of psychiatry and behavioral sciences at Northwestern University Feinberg School of Medicine and senior author of the study.

This segment aired on April 16, 2014.


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