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Casual marijuana use linked to brain abnormalities

By Docta, Apr 17, 2014 | | |
  1. Docta
    Young adults who used marijuana only recreationally showed significant abnormalities in two key brain regions that are important in emotion and motivation, scientists report. The study was a collaboration between Northwestern Medicine® and Massachusetts General Hospital/Harvard Medical .

    This is the first study to show casual use of marijuana is related to major brain changes. It showed the degree of brain abnormalities in these regions is directly related to the number of joints a person smoked per week. The more joints a person smoked, the more abnormal the shape, volume and density of the brain regions.

    This study raises a strong challenge to the idea that casual marijuana use isn't associated with bad consequences," said corresponding and co-senior study author Hans Breiter, M.D. He is a professor of psychiatry and behavioral sciences at Northwestern University Feinberg School of Medicine and a psychiatrist at Northwestern Memorial Hospital.

    Some of these people only used marijuana to get high once or twice a week," Breiter said. "People think a little recreational use shouldn't cause a problem, if someone is doing OK with work or school. Our data directly says this is not the case."

    The study will be published April 16 in the Journal of Neuroscience.

    Scientists examined the nucleus accumbens and the amygdala -- key regions for emotion and motivation, and associated with addiction -- in the brains of casual marijuana users and non-users. Researchers analyzed three measures: volume, shape and density of grey matter (i.e., where most cells are located in brain tissue) to obtain a comprehensive view of how each region was affected.

    Both these regions in recreational pot users were abnormally altered for at least two of these structural measures. The degree of those alterations was directly related to how much marijuana the subjects used.

    Of particular note, the nucleus acccumbens was abnormally large,
    and its alteration in size, shape and density was directly related to how many joints an individual smoked.

    "One unique strength of this study is that we looked at the nucleus accumbens in three different ways to get a detailed and consistent picture of the problem," said lead author Jodi Gilman, a researcher in the Massachusetts General Center for Addiction Medicine and an instructor in psychology at Harvard Medical School. "It allows a more nuanced picture of the results."

    Examining the three different measures also was important because no single measure is the gold standard. Some abnormalities may be more detectable using one type of neuroimaging analysis method than another. Breiter said the three measures provide a multidimensional view when integrated together for evaluating the effects of marijuana on the brain.

    These are core, fundamental structures of the brain," said co-senior study author Anne Blood, director of the Mood and Motor Control Laboratory at Massachusetts General and assistant professor of psychiatry at Harvard Medical School. "They form the basis for how you assess positive and negative features about things in the environment and make decisions about them."
    Through different methods of neuroimaging, scientists examined the brains of young adults, ages 18 to 25, from Boston-area colleges; 20 who smoked marijuana and 20 who didn't. Each group had nine males and 11 females. The users underwent a psychiatric interview to confirm they were not dependent on marijuana. They did not meet criteria for abuse of any other illegal drugs during their lifetime.

    The changes in brain structures indicate the marijuana users' brains are adapting to low-level exposure to marijuana, the scientists said.

    The study results fit with animal studies that show when rats are given tetrahydrocannabinol (THC) their brains rewire and form many new connections. THC is the mind-altering ingredient found in marijuana.
    "It may be that we're seeing a type of drug learning in the brain," Gilman said. "We think when people are in the process of becoming addicted, their brains form these new connections."
    In animals, these new connections indicate the brain is adapting to the unnatural level of reward and stimulation from marijuana. These connections make other natural rewards less satisfying.
    "Drugs of abuse can cause more dopamine release than natural rewards like food, sex and social interaction," Gilman said. "In those you also get a burst of dopamine but not as much as in many drugs of abuse. That is why drugs take on so much salience, and everything else loses its importance."

    The brain changes suggest that structural changes to the brain are an important early result of casual drug use, Breiter said. "Further work, including longitudinal studies, is needed to determine if these findings can be linked to animal studies showing marijuana can be a gateway drug for stronger substances," he noted.

    Because the study was retrospective, researchers did not know the THC content of the marijuana, which can range from 5 to 9 percent or even higher in the currently available drug. The THC content is much higher today than the marijuana during the 1960s and 1970s, which was often about 1 to 3 percent, Gilman said.

    Marijuana is the most commonly used illicit drug in the U.S. with an estimated 15.2 million users, the study reports, based on the National Survey on Drug Use and Health in 2008. The drug's use is increasing among adolescents and young adults, partially due to society's changing beliefs about cannabis use and its legal status.

    A recent Northwestern study showed chronic use of marijuana was linked to brain abnormalities. "With the findings of these two papers," Breiter said, "I've developed a severe worry about whether we should be allowing anybody under age 30 to use pot unless they have a terminal illness and need it for pain"

    April 15, 2014
    Northwestern University
    Young adults who used marijuana only recreationally showed significant abnormalities in two key brain regions that that are important in emotion and motivation, scientists report. This is the first study to show casual use of marijuana is related to major brain changes. It showed the degree of brain abnormalities in these regions is directly related to the number of joints a person smoked per week.

    Jodi M. Gilman, John K. Kuster, Sang Lee, Myung Joo Lee, Byoung Woo Kim, Nikos Makris, Andre Van Der Kouwe, Anne J. Blood and Hans C. Breiter. Cannabis Use is Quantitatively Associated with Nucleus Accumbens and Amygdala Abnormalities in Young Adult Recreational Users. Journal of Neuroscience, April 16, 2014



  1. 5-HT2A
    My problems with the study:

    1) It does nothing to show that the active ingredients in marijuana caused the changes in brain structure; the brains of those who like to smoke pot could simply be wired differently than those who don't like to smoke. A study that showed a brain gradually changing as a person continues to use would be of much more value. This study may not be possible though for ethical reasons.

    2) The study does nothing to demonstrate any functional impairments due to changes in brain structure. If we assume that cannabinoids are responsible, the fact that they alter certain brain structures may be positive or negative or neither. In general we should be wary of such things but at this point there isn't much reason to say either way what this means.

    3) There were only 40 or so people in the study. Too small to generalize.
  2. Joe-(5-HTP)
    This is the main issue with this study as I see it, though it certainly seems like cause for concern.

    Hopefully they do more research on this.
  3. detoxin momma
    this study is bullshit in my opinion.
    as soon as i got to abnormalities in motivation i disagreed completely.

    ive been smoking pot for a very long time.and im a motived person.im very active.even if its just at home.always have been.always been stoned to.

    everyone in my family for that matter.we all hold down high pressure very self motivated jobs.all of us self employed.we rely on our motivation.and we all get stoned after work.thats the only life ive known.
    if marijuana does impair your motivation then youre either smoking too much,or its not the drug for you.in my opinion.

    i dont think thats enough people they tested to really get accurate numbers either.

    so yeah,i think that study needs a little more work,and alot more people
  4. BenThereDude
    Been smoking for forty years and had always been motivated to get the job done now I have found a bigger motivator ; to fight Parkinson's and part of my arsenal is ........you guessed it marijuana !
  5. idfma
    That pretty much sums it up. I couldn't agree more DM.

    The thing that jumped out at me was the bias in the researchers' comments. They are clearly motivated to prove the danger and negative consequences of even casual use. 'We know that shit is evil, and we'll damn well prove it.'

    Also, I didn't really see where they explained how it affects motivation...only that it does. They think marijuana is solely responsible for the observed changes in the brain (they never explain how they are that certain), from there they conclude that change can only be bad. They put a nice ribbon on it by dragging out the tired, overused, completely unproven 'gateway drug' theory. Can't we just put that ol' girl out to pasture--she's done.

    We'll now I'm beating a dead horse. What I found most disgusting and disturbing is the researchers are already deciding what they've seen is bad before they even understand what they're looking at. So much for the scientific method.
  6. Appeal to Novelty
    Spreading this study far and wide just drums in the message that smoking marijuana is somehow worse that alcohol and should be re-criminalized. Personally, when I see stupid studies like this, I ignore them. In fact, this is the first time I've responded to this thing (that I've seen about a dozen times online).
  7. TheBigBadWolf
    I dont like to be in the smells like bullshit/must be bullshit fraction.
    And of course driving cars is more dangerous than smoking Cannabis.
    That should not take the view off that driving cars whilst being UTI is unsafer than each of the two on their own.

    Certainly the number of testees is too small, - but that doesnt give anyone a reason to condemn that questions are questioned, what we have to say is :

    Has to be researched further and deeper.

    The study was too small to give us certainty, but it piints on stuff we ll have to take closer looks to.


    Tried it 3 times and always got out BBQ. Is this normal or does the universe make fun.of me ( I mean what else would it have to do, that damn lazy universe...)
  8. Joe-(5-HTP)
    I don't think people should be so quick to dismiss this study.

    Sure I would love cannabis to be totally safe, but maybe it's not.

    This study doesn't tell us anything about whether these brain abnormalities actually mean anything. But it doesn't claim that they do either. The study is simply saying this is cause for concern, and they are right. More research is needed.

    Maybe this will add fuel to the prohibition movement. But let's be better than them. Let's embrace and accept the truth, no matter what it is.

    Remember all the lies they spread about cannabis. Remember how little they care about the truth.

    Let's be different.
  9. TheBigBadWolf
    Good call Joe.

    What we must not do is show the seen-too-often attitude of doesnt fit my agenda so I dismiss it.

    Thats exactly the attitude the abolishionists show since Anslinger's days.

    If there are hints to possibly harmful.effects (which is not even begun to think about in the study) we have to take them and see how one / if one can safely proceed to consume under the newly found circumstances.

    World didnt remain flat cos someone wanted it to....

  10. idfma
    You make a good point, Joe. I agree: if it's harmful, I want to know as much about that as possible. The clear agenda of those doing the research is where the bulk of the bullshit is.
  11. venkecske
    An earlier study reported similar findings, especially for amygdala:

    Yücel M, Solowij N, Respondek C, Whittle S, Fornito A, Pantelis C, Lubman DI:
    Regional brain abnormalities associated with long-term heavy cannabis use.
    Arch Gen Psychiatry 2008; 65(6): 694-701

    CONTEXT: Cannabis is the most widely used illicit drug in the developed world. Despite this, there is a paucity of research examining its long-term effect on the human brain.
    OBJECTIVE: To determine whether long-term heavy cannabis use is associated with gross anatomical abnormalities in 2 cannabinoid receptor-rich regions of the brain, the hippocampus and the amygdala.
    DESIGN: Cross-sectional design using high-resolution (3-T) structural magnetic resonance imaging.
    SETTING: Participants were recruited from the general community and underwent imaging at a hospital research facility.
    PARTICIPANTS: Fifteen carefully selected long-term (>10 years) and heavy (>5 joints daily) cannabis-using men (mean age, 39.8 years; mean duration of regular use, 19.7 years) with no history of polydrug abuse or neurologic/mental disorder and 16 matched nonusing control subjects (mean age, 36.4 years).
    MAIN OUTCOME MEASURES: Volumetric measures of the hippocampus and the amygdala combined with measures of cannabis use. Subthreshold psychotic symptoms and verbal learning ability were also measured.
    RESULTS: Cannabis users had bilaterally reduced hippocampal and amygdala volumes, with a relatively (and significantly) greater magnitude of reduction in the former (12.0% vs 7.1%). Left hemisphere hippocampal volume was inversely associated with cumulative exposure to cannabis during the previous 10 years and subthreshold positive psychotic symptoms. Positive symptom scores were also associated with cumulative exposure to cannabis. Although cannabis users performed significantly worse than controls on verbal learning, this did not correlate with regional brain volumes in either group.
    CONCLUSIONS: These results provide new evidence of exposure-related structural abnormalities in the hippocampus and amygdala in long-term heavy cannabis users and corroborate similar findings in the animal literature. These findings indicate that heavy daily cannabis use across protracted periods exerts harmful effects on brain tissue and mental health.

  12. Dr.Evil
    This an interesting study that warrants further research into (possible) marijuana-induced brain changes. Being a person who has to analyze new medical/scientific info on a regular basis the only thing this study tells me is that more study needs to be done.

    Problems with the study:
    1) extremely small sample size - 20 in each group is almost laughable in terms of statistical power
    2) groups were only matched on age, race, sex, handedness, and years of education - in other words most medically relevant matching was not done
    3) almost half of the marijuana group reported smoking cigarettes "occasionally" while none of the controls were smokers - this could easily account for some of the brain changes seen
    4) the marijuana group drank 3 more drinks per week on average than the control group - while this doesn't seem like a lot this figure is almost always under-reported and in such a young age group could affect brain development more than the number of drinks would indicate
    5) they did not exclude anyone from the marijuana group or even have data on other drug usage - this is a huge error in the study

    This is a great study overall (I don't want to come across like I think it is bogus), but people tend to draw the wrong conclusions when these headlines come out. All this study means (in the medical world) is that the jury is not yet out on whether marijuana is "safe" or not. I uploaded the actual study below for anyone interested in reading it.

  13. detoxin momma
    i to feel like i would like to be as informed as possible about anything im consuming.
    i appreciatte the study as a whole,what the scientist are trying to prove and find out.

    i most definatly would want to know if they discovered some cold hard facts about marijuana harming/impairing your brain functions.

    but i really think they would need 100s of people consuming exact same things for the exact amount of times,etc.and thats very unlikely to test that many people that are so much alike.

    marijuana affects everyone differently.just like everything else does.some people get hyper from sugar,some get tired.some people get irratible on caffeine,some dont.some people are allergic to peanuts etc etc.

    i dont think its accurate to ever say "marijuana causes....."
    because everyones brains are wired differently.

    thats why i call bullshit.i would never buy into it causing any specific occurence for people as a whole.
  14. Docta
    There are 28 reference documents that need to be read in conjunction with the discussion section of this paper, how did you all get through them so fast?

    The only result statement is:" results of this study indicate that in young, recreational marijuana users, structural abnormalities in gray matter density" that doesn't sound surprising.

    All drug addiction has a price, you cant call the selectively cultivated shit they smoke today cannabis. Its a hybrid focused on a principal psychoactive constituent with no regard for the other four or five hundred compounds that make up the cannabis plant. Tetrahydrocannabinol (THC) is all that seems to matter these days so let me state this clearly so these can be no misunderstanding.

    Mainly as a result of current White house policy the Office of National Drug Control Policy has blocked any research into the possible medical implications of THC drugs that no longer contain sufficient quantities of cannabidiol (CBD), cannabinol (CBN), tetrahydrocannabivarin (THCV) and cannabigerol (CBG) to allow the THC drug to fall under existing cannabis toxicology.

    There’s a paper out of Poland: Tetrahydrocannabinols in clinical and forensic toxicology by the Faculty of Chemistry at Jagiellonian University that give some information but its to old (2005) and not defined enough to give definitive answers for the safety of habitual use of THC drugs.

    Are the new wave of supper high content THC drugs safe? nobody knows.
  15. TheBigBadWolf
    I guess we will have the answers in two generations of heavy cannabis smokers and their children.

    Humankind is outbreeding these test results for those who can see.

    With the modern high THC strains there definitely is some difference to what we were smoking in the eighties. I can't imagine what had happened to my brain if I had had the access to the cannabis drugs fifteen year olds have today.

    Two weeks ago I ran into a batch of Marijuana - which is very rare for me, I tend to smoke hash for some reasons - and this again showed me that with the experienced user I certainly am, I nearly had overdosed myself in terms of being too high to be able to interact with others.

    From my 'youth', between 15 and 19 I mean, I remember days of intense smoking without anybody having anxiety attacks or psychotic episodes.
    He who didnt listen not to drink beer learned it made them puke. That was all the issues that appeared.

    I've read on a post here:
    what is that telling us? Not just that nobody asked themselves why these things are called JOINT *facepalm* but that the users didnot have a real idea what they were doing there, each one smoking a joint of probably potent marijuana.
    And Europeans who say they mix tobacco in joints are looked at funnily?

    well, I guess none of the Grampas of the member who wrote the above and their friend have given their weed experiences to the grandsons.
    Because it's forbidden.
    Because you dont talk about what you did was forbidden.

    Thats what the abolishionists mean when they say that cannabis has no cultural background in western society. And they are right.
    When my generation and the ones that come, doesnt begin to give eperience reports to the younger ones there will follow some further hundred years of getting forbidden what nobody has they right to forbid.

    There is the experience around, out there. They'll all only need to open their mouths.

    Sorry for leading this thread off topic.

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