"Using marijuana a few times a week is enough to physically alter critical brain structures," wrote Karen Weintraub wrote on April 15 in USA TODAY.
That might be true. Then again, maybe not. The problem is that Weintraub doesn't know whether it's true, and neither do the authors of the study on which her story was based.
Sadly, the lead author of the study, which appeared in the Journal of Neuroscience, thinks he knows. Hans Breiter of Northwestern University told Weintraub that "just casual use appears to create changes in the brain in areas you don't want to change."
In a blog post at MedPage Today, John Gever had little patience for the coverage of this study, in USA TODAY and elsewhere.
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.
The problem is that the researchers looked at only 20 subjects and 20 controls, and they took only one snapshot of their brains. They found differences in the brains of marijuana users and controls, but they can't say anything about what that means on the basis of one set of pictures.
Did the marijuana users' brains change over time? Were the differences, with such a small population, due to chance? And did marijuana use cause the differences, or do the differences reflect something that encourages people to use marijuana? "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," Gever wrote.
The study did find differences in the brains of users and controls, but what that means is anyone's guess. And much of the coverage talked about "changes" in the users' brains, a more loaded word than "differences."
But the coverage marched forward, indicting marijuana with all the glee and recklessness of Reefer Madness. "Study finds brain changes in young marijuana users," was the headline on Kay Lazar's story in The Boston Globe. "Recreational Pot Use Harmful to Young People's Brains," topped the story by Randye Hoder at TIME. Hoder found it necessary to use an exclamation point to underscore the "findings" of the study:
A new study from medical researchers at Harvard and Northwestern shows that 18- to 25-year-olds who smoke marijuana—even just recreationally!—had marked abnormalities in areas of their brains that regulate emotion and motivation.
Terrifying, isn't it? There's no way to know whether marijuana use–even just recreationally!–caused the changes, but as the old saying goes, never let the facts get in the way of a good story.
There were many other stories along those lines, but not everyone was fooled.
For more–much more–on the issues that Gever raised, you can turn to a blog post by Lior Pachter, a professor of molecular and cell biology, mathematics, and computer science at the University of California, Berkeley. In a post on his Bits of DNA blog, he wrote that "this is quite possibly the worst paper I've read all year."
Pachter has an impressive title, but reporters shouldn't have required fancy academic credentials to see the problems with this story.
What is perhaps most disturbing is that not only did the author of the study misrepresent the results, the Society for Neuroscience did so as well, in a press release headlined–you guessed it–"BRAIN CHANGES ARE ASSOCIATED WITH CASUAL MARIJUANA USE IN YOUNG ADULTS."
Reporters who relied on that release remind me of the student who fails his test because he copies the wrong answers from the kid sitting in front of him.
The release might help explain why the coverage was so bad. But it's no excuse.
-Paul Raeburn
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