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Latest JAMA Studies Largely Fail To Support Past Claims About Marijuana And Brain Health


marijuana creativity brainBy Paul Armentano, NORML Deputy Director

Two new studies published online today in JAMA (Journal of the American Medical Association) Psychiatry provide little support for previous claims that cannabis exposure is significantly harmful to the developing brain.

The first study, which assessed the effects of cannabis exposure on brain volume in sibling pairs, reported that any identifiable differences “were attributable to common predispositional factors, genetic or environmental in origin.” By contrast, authors found “no evidence for the causal influence of cannabis exposure” on brain morphology.

The trial is “the largest study to date examining the association between cannabis exposure (ever versus never used) and brain volumes.”

The study is one of two recent clinical trials to be published in recent months rebutting the claims of a widely publicized 2014 paper which alleged that even casual marijuana exposure may be linked to brain abnormalities, particularly in the region of the brain known as the amygdala. In January, researchers writing in The Journal of Neuroscience reported “no statistically significant differences … between daily [marijuana]users and nonusers on [brain]volume or shape in the regions of interest” after researchers controlled for participants’ use of alcohol. Similarly, today’s JAMA study “casts considerable doubt on hypotheses that cannabis use … causes reductions in amygdala volumes.”

A second study appearing today in the journal assessed whether cannabis use during adolescence is associated with brain changes that may be linked to an increased risk of schizophrenia. While researchers reported finding an association among male subjects who possessed a high genetic predisposition toward schizophrenia, authors reported that no such association existed among male subjects who were at low risk for the disease, or among females in either the high risk or low risk categories. The finding is consistent with the theory that early onset cannabis use may potentially exacerbate symptoms in a minority of subjects predisposed to the disease, but it contradicts claims that marijuana exposure is a likely cause of schizophrenia, particularly among those who are not already vulnerable to the disease.

Abstracts of both new studies appear online in JAMA Psychiatry here and here.

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Johnny Green


  1. This makes me want to say..” Who is getting a big Grant from Big Pharm”? JAMA ” just ” didn’t forget to omit the current research and evidence to show the benefits of cannabis and brain health and recovery! This of is deliberate neglect!

  2. They are out kicking down doors shooting dog’s, people
    And eradicating legal mmj garden
    And the FDA claims the active ingredient in “Agent orange”
    Is safer for human consumption
    Citing ” multiple government studies”
    See ASPERTAME /Donald Rumsfeld

  3. Where is the DEA and FDA? Approving the most addictive drug in the history of our country Oxycontin, for use by our children.

  4. #prohibition and the #bullshit they claim cannot be replicated.
    I remember the 90’s when they (big pharma ) started pushing dope on children, legal dope Ritalin ,Prozac adderall etc.
    All claimed to increase “dopamine”
    And return a balance in chemistry with in our bodies! !
    And now with the knowledge of the endocannabinoids and the ECS
    Turns out they we’re lying to push their dope!
    Oxycontin – profits in the billions while thousands die or are enslaved to opiates .where is the DEA on this?
    Cannabis Is safer than tap water
    Yet they put it in schedule 1
    $$$ they are hooked on Cannabis #prohibition

  5. Yet I promise you that Prohibitionist will continue to use the information from the NON peer reviewed study that was performed. Yet paid for by NIDA. The agency most singly responsible for stifling research on this plant.

    Yeah…. I’m gonna trust their opinion eh? It’s NOW been refuted TWICE w/in 1 year after being peer reviewed.

  6. If the research community spent this much time researching the effects of alcohol and publicizing them, liquor stores would be empty.

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