This week a study of cannabis consumers published by The Journal of Neuroscience provided powerful evidence that MRI scans cause shoddy science reporting. Researchers at Northwestern University and Massachusetts General Hospital used MRIs to compare the brains of 20 young adults who reported smoking pot at least once a week and 20 controls who had used marijuana no more than five times in their lives and had not consumed it at all in the previous year. The pot smokers had higher gray-matter densities in the left nucleus accumbens, and there were “significant shape differences” between subjects and controls in that area and in the right amygdala. The differences were more pronounced in subjects who reported smoking marijuana more frequently. “Because this is a cross-sectional study,” the authors noted, “causation cannot be determined.” In other words, it is not clear whether the brain differences were caused by marijuana. It also is not clear how long the differences last or whether they have any functional significance.
Those nuances generally were lost in press coverage of the study, which presented the MRI scans as evidence that smoking pot causes brain damage. News outlets claimed the study found that “marijuana re-shapes brains of users” (NBC News), that “even casually smoking marijuana can change your brain” (The Washington Post), that “casual pot use impacts brains of young adults” (The Oregonian), that “recreational pot use” is “harmful to young people’s brains” (Time), that “casual marijuana use” is “bad for young adults” (The Times of India), and that “even ‘casual’ marijuana use can knacker bits of your brain” (Gizmodo UK). A Medical News Today headline quoted the researchers as saying “casual marijuana use changes the brain,” although that statement does not appear in the article under the headline, in the study itself, or in press releases about the study issued byNorthwestern University, Massachusetts General, and the Society for Neuroscience, which publishes The Journal of Neuroscience. Similarly, an MSN NZ headline had the study claiming that “cannabis use ‘alters brain regions,’” another phrase that is absent from the study and the press releases.