Correlation does not equal causation, and a single exam cannot show a trend over time. Basic stuff, right?
But judging by coverage of a study just out in the Journal of Neuroscience, these are apparently foreign concepts for many folks in the media.
In the study, researchers at Boston’s Massachusetts General Hospital and Northwestern University in Chicago performed MRI brain scans on 20 young adult “casual” marijuana users and 20 age- and sex-matched nonusers. They found that, in the users, gray matter densities in the nucleus accumbens were higher than in controls, and the right amygdala and left nucleus accumbens were shaped differently.
Interesting, but remember that these findings only reflected differences between the marijuana users and controls at a single point in time. The researchers did not, could not, demonstrate that the differences resulted from marijuana smoking or even that the “abnormalities” relative to controls reflected changes from some earlier state.
You wouldn’t know that from the media coverage.
RTFA for a small sampling of almost universal crap
…Note that the study did not identify any cognitive or behavioral abnormalities in the cannabis users versus controls — it was strictly an MRI study.
That, however, didn’t stop senior author Hans Breiter, MD, of Northwestern from opining in the SfN press release that the study “raises a strong challenge to the idea that casual marijuana use isn’t associated with bad consequences.”
Um, no, it doesn’t — not without before-and-after MRI scans showing brain structure changes in users that differ from nonusers and documentation of functional impairments associated with those changes.
Further studies may – or may not – indicate one or another cause-and-effect relationship. That kind of study must be constructed differently than this one. And hopefully the press release and editors who get the email won’t be in a hurry to construe the study as something it isn’t.