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

  • by Paul Armentano, NORML Deputy Director August 26, 2015

    Latest JAMA Studies Largely Fail To Support Past Claims About Marijuana And Brain HealthTwo 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 exposed and unexposed 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.

    17 responses to “Latest JAMA Studies Largely Fail To Support Past Claims About Marijuana And Brain Health”

    1. rah lam says:

      What I said all along was..if you have a predisposition to mental illnesses and smoke marijuana…you may have a problem. But a healthy brain won’t be screwed up by marijuana use. These studies solidify this hypothesis

    2. Linda Harris says:

      I had to sumit to a drug test for my P.C.P that perscribes my meds, at the time i was on a very strong antibiotic and had a bad kiddney infection and had been flushing my system for 4 or 5 days prior to help me with Viniger, cranberry, and lots of water to get rid of the infection, so when I took pee test a few days later the dr. called me in and said I had to go to pain clinic? he said I did not have the Adivan and Norco in my system for 5 day’s? I did take my med’s but he insisted i did not, how can I prove myself??? help

    3. Galileo Galilei says:

      So we find one more the ir-reproducible study the prohibitionists have seized upon to justify their anti-marijuana zealotry.

      Sadly, it’s not like this is something new under the sun.

    4. TheOracle says:

      Would the real Dr. Kevin Sabet now shut the f**k up?! Sabet, your name is pronounced in French like Sabay as in Dr. Bombay, you freaking prohibitionist quack! Call off the witch hunt.

    5. mexweed says:

      The threat of shame, punishment, blacklisting etc. might be enough to explain mental illness in some individuals, or maybe the unhealthy emphasis on habitual secrecy and seclusion to avoid being caught.

      Cannabis legalization will remove the need to avoid detection by means of the easy-to-hide, hurriedly-used-up joint. No longer fear to possess and carry your flexdrawtube one-hitter.

      Apparently no one disputes the interesting statistic that 80% of schizophrenia patients are hot burning overdose monoxide nicotine $igarette addicts. Worth remembering that an Australian Department of Health document has described joint-$moking (esp. blunt, $pliff) as a “Trojan Horse” luring youngsters into nicotine $igarette addiction.

    6. Todd says:

      I think mental health means simply knowing we don’t each have a computer inside our face. People are societal not monolithic.

    7. john finzel says:

      It’s about time that someone came out with some real science that supports what people have been saying all along. Cudo’s to JAMA.

    8. Brad says:

      Grasping at straws

    9. delai says:

      Marijuana has been ILLEGAL for over 70 years!
      What are the results?

      *Today marijuana is America’s #1 cash crop.

      *Today American kids can buy marijuana easier than they can buy a beer.

      *Marijuana is stronger and easier to get than ever before, albeit much more expensive than it should be. To smoke casually from the “black market”, it will run you $100/month. This is much more expensive than it needs to be. More expensive than my cell phone ($20/month from Tmobile), car insurance ($25/month from Insurance Panda), netflix ($10/month), and gym ($15/month from PF) COMBINED!!! Would you rather put money into the hands of violent gangs and drug dealers… or into taxes for schools, hospitals, public infrastructure, etc.???

      *Today marijuana is the #1 source of income for violent drug gangs and drug cartels who are richer and more dangerous than ever before.

      *Guns are illegal in Mexico yet Mexican drug cartels are buying machine guns, rocket launchers, grenades, airplanes, armored vehicles, anti-aircraft guns, and even submarines.

      *There are over half a million Americans in jail right now for non-violent drug crimes.

      *The DEA has been having sex parties funded by drug cartels.
      The ATF/DOJ has given thousands of guns to drug cartels.

      I have this stupid thing I do called THINKING, and clearly I can see that marijuana prohibition can never work! America should have learned this simple lesson from alcohol prohibition!

    10. Kristi M says:

      If you have a drug urine test and it’s not showing up correctly, I would highly advise your Dr’s to do a genetic test (cheek swab) to check the enzymes in your liver to see if you are correctly metabolizing your medications.