Researchers Clarify Findings behind Study of Casual Marijuana Use and Brain Abnormalities

In light of media confusion, researchers clarified the findings behind their study about how brain changes are associated with casual marijuana use.

Headlines Wednesday included "Casual marijuana use linked to brain changes," "Marijuana re-shapes brains of users, study claims" and "Casual marijuana use may damage your brain."

This frustrated the study's authors, who said such statements missed the point.

"I think I saw one headline that was 'Marijuana reshapes the brain' and I groaned - that's not what we did," Dr. Jodi Gilman told PolicyMic in an attempt to explain what had been lost in translation.

"The conclusions were modest in the paper - we never say marijuana causes these changes," said Gilman, who's a neuroscientist with a Ph.D. from Brown University. "The media may have given that impression in headlines, but the study doesn't show causation."

What the collective team from Northwestern University and Massachusetts General Hospital/Harvard Medical School said was that casual marijuana use may (key word "may") be linked to abnormalities found in the brain.

Certain regions of the brain of people involved in the study who smoked marijuana were structurally different than people who did not, according to the results published in The Journal of Neuroscience.

Researchers compared the brains of 40 Boston-area college students, ages 18 to 25. Half of the participants used marijuana at least once a week and the other half were non-smokers. The smokers in the study started using marijuana between the ages of 14 and 18, but were not dependent on the drug.

Using magnetic resonance imaging, Gilman and her colleagues found that the experimental group had structural differences in the nucleus accumbens and the amygdala regions of their brains - both of which relate to motivation and emotion.

But as the maxim goes, correlation does not imply causation. For example, people who use marijuana at a young age may have natural differences in their brains. Moreover, these differences don't necessarily have to be associated with negative effects.

"The main point is there are differences in the brains of these two groups. The subtly is we don't know if those differences are causal and relate to function or behavior," Gilman said.