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

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 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 thoughts

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

  7. 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. 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!

  9. 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.

  10. Cannabis consumers would have all doctors on our side if we could just guarantee them a profit from our endeavors. Profiting from our healthcare decisions is the basis of their economic efforts. It should be the health of their patients, but their use of petrol-chemical based medications killing millions world wide and just paying a higher premium to their malpractice insurance carriers has the public questioning their oath.

  11. It must really stink in there to be a prohibitionist right now.

    Well Feinstein and Grassley; You wanted more evidence? Heeeeeeeeeere you go! (Because U.S. Patent 6630507 on “cannabinoids as neuroprotectants” owned by the Department of Health and Human Services REALLY wasn’t enough, y’know?)
    As to other comments on mental health, if you have a predisposition to schizophrenia lay off the high THC and pick a Charlotte’s Web strain of cannabis high in CBD. (No pun intended; I guess we’re all high in something… Whether its psychoactive or anti-psychoactive…)

  12. 1950Most ogf these die-hard prohibitionists are from the (born from 1950 to 1955) group). As long as this generation holds the committee reigns, I don’t look for much to change. It’s hard to separate people from both parties from their power.

    The same intrusive, overbearing and totalitarian forces in government that the tea party wore out at nauseum are now forced to face their own small government hipocracy. In fact, the drug war was used to win over conservatives to the idea of a totalitarian state. That is to say that, the drug war set the very precedent.

    With this generation entering their twilight years, It’s going to be interesting to see how the electoral demographics are going to look like as we approach 2016.

  13. @Raven,
    I’m 37 and know how my generation is moderately mota-vated to vote, but as we know during Presidential elections younger people are frequently compelled to vote, and it’s interesting to watch Bernie Sanders (being of elder age) stir up so many young progressive voters. All he has to do is show that same passion against the establishment by renouncing the drug war and Hillary could end up with a run for her money, even if she is smart enough to get HUD Secratary Julian Castro as her running mate.
    I help many latinos here in Texas prepare their immigration forms, and frequently I get asked “Do you think Trump could win?” And to them I reply, “if more latinos and young people don’t vote, it’s possible. If residents dont become citizens, if people just stay home, even an over-priced, loud and angry money-washing machine like Trump has a chance.
    While we listen to Trump spill similar rhetoric that Anslinger used to pass the marijuana stamp act of 1937, the irony is that the majority of central americans entering legally or illegally are no longer entering looking primarily for work; theyre drug war refugees escaping a war caused directly by U.S. Drug policy, and deliberate corporate exploitation by using US AID and the DOJ to topple Democratically elected latin leaders, such as what Food Inc did to Guatemala in the 50s (and the country is STILL in civil war). As Delai points out, the ATF has been in the business of selling arms to both warring cartels and governments alike. And unlike what Trump has to say, “sending rapists and murderers” it is our USCIS that deports dangerous criminal gang leaders, rapists and murderers to latin countries WITHOUT informing said nation of the criminal history the deportee developed HERE in the US.
    Fortunately the younger voting generation grew up with smart phones and internet access.

  14. This does not surprise me at all. It seems that the results of a great many psychiatric studies can’t be reproduced. It is probably even more likely that any study involving marijuana would be hard to reproduce, by a group doing real research, considering the incredible bias against it by the rich and powerful prohibitionists (e.g. Nixon, Biden, Reagan, Bush…).

  15. Julian; I couldn’t agree more. Convincing the young people to vote like the older generation says is everyone’s duty as a citizen (ironically the prohibitionist’generation’s mantra) is the challenge. They just don’t realize their own electoral power. This is due (partially) to instant gatification. That is to say that,”things just don’t change fast enough fo me so forget it.”

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