Heavy and prolonged use of marijuana changes the way the brain functions and can lead to poor memory, according to a new study — but the study only used 10 healthy people with a history of cannabis use (it also tested 15 young people with a history of cannabis use and schizophrenia). Even the lead researcher admits that the changes seen could have resulted in marijuana use, rather than the other way around.
The study is being played up heavily in the mainstream press, with many of the news accounts not mentioning that only 10 non-schizophrenic marijuana users were studied. With future policy debates likely to reference this study as a reason not to relax the laws around cannabis, the credulous acceptance and lack of critical coverage of the study is quite unfortunate.
The study, based on data obtained from teens and young adults, was conducted by researchers at Northwestern Medicine, reports Nature World News. Researchers said they found chronic cannabis use led to poor growth of the brain region associated with memories.
According to the study, heavy marijuana users also had “differences in brain structures” resembling those seen in schizophrenia patients. But the scientists said “it is possible” that their existing brain differences made them more likely to smoke marijuana in the first place, reports Ellie Zolfagharifard at The Daily Mail.
The study only had 67 participants, including controls. Test subjects in the study began using cannabis when they were 16 to 17 years old. The test volunteers hadn’t used marijuana for about two years at the time of the research.
Scientists used magnetic resonance imaging (MRI) to assess changes in deep subcortical gray matter of marijuana users and compared the results with non-users and schizophrenia patients. Researchers said the study showed cannabis is “linked with” poor working memory ability.
Working memory is the ability to store information for short-term use; for instance, people who are good at math have a good working memory.
“The study links the chronic use of marijuana to those concerning brain abnormalities that appear to last for at least a few years after people stop using it,” claimed lead study author Matthew Smith, assistant research professor in psychiatry and behavioral sciences at Northwestern University Feinberg School of Medicine.
“We see that adolescents are at a very vulnerable stage neurodevelopmentally,” Smith said, reports Brian Alexander at NBC News. “And if you throw stuff into the brain that’s not supposed to be there, there are long-term implications for their development.”
Smith’s off-hand commend to the press reveals that he needs to educate himself more about the human endocannabinoid system — because if he did so, he would know that cannabinoids are “supposed to be there” in the brain, and in fact many important functions would be thrown into imbalance if they weren’t.
Even Smith stressed that the study does not prove cause and effect. The differences in brain structure in Smith’s study could have existed before the young people ever used marijuana — and made them more likely to use pot in the first place. The fact that none of thousands of other studies have shown such brain differences in cannabis users certainly leads one to suspect this may be the case.
“We can identify certain differences, mainly in impulse control, related to the onset of substance use,” Dougherty said. “But the key thing is that we do not know what impact drug use has on normal development. It may be that differences at the beginning leads to drug use, then drug use also impacts normal development. We can’t tease these things out.”
Dougherty said the study was “very interesting” but agreed with Smith that “there are lots of unanswered questions.” Ideally, researchers would follow children from a time before they ever started using, through a period of use, and into adult years to track brain and cognition changes.
The study article is published in the scientific journal Schiophrenia Bulletin.
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