Casual marijuana use may damage your brain
April 16th, 2014
09:02 AM ET

Casual marijuana use may damage your brain

If you thought smoking a joint occasionally was OK, a new study released Tuesday suggests you might want to reconsider.

The study, published in the Journal of Neuroscience, is the first to link casual marijuana use to major changes in the brain. And according to the researchers, the degree of abnormalities is based on the number of joints you smoke in a week.

Using different types of neuroimaging, researchers examined the brains of 40 young adults between the ages of 18 and 25 who were enrolled in Boston-area colleges. Twenty of them smoked marijuana at least once a week. The other 20 did not use pot at all.

The marijuana smokers were asked to track their cannabis use for 90 days. All were given high-resolution MRIs, and users and non-users' results were compared.

Researchers examined regions of the brain involved in emotional processing, motivation and reward, called the nucleus accumbens and the amygdala.  They analyzed volume, shape and density of grey matter - where most cells in brain tissue are located.

"I think the findings that there are observable differences in brain structure with marijuana even in these young adult recreational users indicate that there are significant effects of marijuana on the brain," says Dr. Jodi Gilman, lead author and a researcher in the Massachusetts General Center for Addiction Medicine. "Those differences were exposure-dependent, meaning those who used more marijuana had greater abnormalities."

More than a third of the group - seven of the 20 - only used pot recreationally once or twice a week. The median use was six joints a week, but there were four people who said they smoked more than 20 joints a week. None of the users reported any problems with school, work, legal issues, parents or relationships, according to Dr. Hans Breiter, co-senior author of the study and a professor of psychiatry and behavioral sciences at Northwestern University Feinberg School of Medicine.

"There's a general idea out there that casual use of marijuana does not lead to bad effects, so we started out to investigate that very directly," Breiter said. "This research with the other studies we have done have led me to be extremely concerned about the effects of marijuana in adolescents and young adults and to consider that we may need to be very careful about legalization policies and possibly consider how to prevent anyone under age 25 to 30 from using marijuana at all."

Researchers have long been concerned about the effects of marijuana on the developing brain - teens and adolescents under the age of 25. Preliminary research has shown that early onset smokers are slower at tasks, have lower IQs later in life and even have a higher risk of stroke.

Dr. Staci Gruber, director of the Cognitive and Clinical Neuroimaging Core at McLean Hospital in Boston and a professor of psychiatry at Harvard Medical School, has conducted numerous studies on marijuana use and brain function.

"This data certainly confirms what others have reported with regard to changes in brain structure," she said. "When we consider the findings of the Gilman ... study with our own and other investigations of marijuana use, it's clear that further investigation is warranted, specifically for individuals in emerging adulthood, as exposure during a period of developmental vulnerability may result in neurophysiologic changes which may have long-term implications."

Gruber says we need to take a closer look at all pot users whether they smoke once or twice a week or four or time times a week.

And she had this advice for adolescents: "Don't do it early–prior to age 16. That's what our data suggests, that regular use of marijuana prior to age 16 is associated with greater difficulty of tasks requiring judgment, planning and inhibitory function as well as changes in brain function and white matter microstructure relative to those who start later."

According to the National Survey on Drug Use and Health, in 2012 nearly 19 million Americans used marijuana. It's the most-used illegal drug in the country and use is increasing among teenagers and young adults.

Results of the new study match those of animal studies, authors say, showing that when rats are given tetrahydrocannabinol, or THC - the ingredient in marijuana the gets you high - their brains rewire and new connections are formed.

Gilman thinks when people start to become addicted to substances, their brains form these new connections too.

"The next important thing to investigate is how these structural abnormalities relate to functional outcomes," she said. "Currently we don't know how much marijuana is safe and I think this study shows that we should be cautious about marijuana use in adolescents and young adults whose developing brain may be even more susceptible to cannabis-induced changes."

soundoff (961 Responses)
  1. Lyuben

    Read the first paragraph of the above news aricle and compare it to the actual participants in the study who, on average, smoked 11.2 joints a week!


    April 19, 2014 at 06:54 | Report abuse | Reply
    • Eeyore

      Compare what? Do you have the slightest clue what the study says? Did you read it? Doesn't appear so.

      April 19, 2014 at 09:18 | Report abuse |
    • Lyuben

      I did read the full study, yes. I should also say I am a cognitive neuroscientist, if you are doubting my ability to comprehend it.

      The news article begins with the statement "If you thought smoking a joint occasionally was okay..." and goes on to explain that the study suggests otherwise. Here's the problem. The study showed that it was not okay to smoke 11.2 joints a week, since that is what their participants did. Do you consider that to be "smoking ocasionally"?

      Not to mention how weak the so-called negative effects are even for those heavy smokers.

      Not to mention that this is a correlation study.

      Not to mention many other problems I don't feel getting into because I am typing from my phone.

      What exactly is your problem with my criticism of CNN's article? You don't think it's misleading at all?

      April 19, 2014 at 09:33 | Report abuse |
    • Eeyore

      While the lead into the story may be misleading, the facts remain: while this is a small study, the results are good reason for concern, and CNN isn't the only news source to conclude that. I don't care what you claim to be; anyone can pretend to be anything on an anonymous site. If you can cite a study that shows these findings to be without merit, do so. Otherwise, nobody has any reason to pay you any mind at all.

      April 19, 2014 at 11:10 | Report abuse |
    • Eeyore

      Oh, and I just LOVE the "many other problems I don't feel like getting into because I'm typing on my phone." Sure.


      April 19, 2014 at 11:15 | Report abuse |
    • bartonizer

      Eeyore, there's no doubt that consumption of a substance or even the participation in an activity can cause changes to the brain. But what do the changes mean in the overall picture? Are changes always bad or even permanent? And how do other things in life affect the brain? One of the two regions of the brain examined in the study is the amygdala. In this article, the study's author implies that the increased size of the amygdala seen in marijuana users is a negative thing. But in the Boston Globe, Dr. Breiter also remarks that cocaine use shrinks the amygdala. Would he suggest that marijuana users balance themselves with a little coke? Context would be helpful, as would unbiased longitudinal studies that accounted for multiple factors. Researchers making blanket generalizations from a limited, cross-sectional study involving self-reporting subjects seems disingenuous at best. And no, it's not just people that you dislike that find the conclusions drawn from the study ridiculous. Here's the take from a leading medical news service on the resulting "reefer madness": http://www.medpagetoday.com/Neurology/GeneralNeurology/45290

      April 19, 2014 at 11:49 | Report abuse |
    • Lyuben

      I am aware that CNN is not the only website who reported this, I am not sure why that matters.

      So, this study shows that smoking 11 joints/week does something to your brain. I have two questions for you:

      1. What conclusions can we draw from these findings for somebody who smokes, say, 1 joint/month?
      2. Since you seem to have read and understood the study, please explain what exactly are the harmful effects of marijuana for heavy smokers according to the study? For instance, one of the very few statistically significant results is that the right amygdala of marijuana smokers has a gray matter density of 0.34, whereas the corresponding GMd for non-smokers is 0.33. Could you comment on the dangers of this finding (or other findings you wish to comment on from the paper)?

      April 19, 2014 at 11:56 | Report abuse |
    • Eeyore

      You two don't get it. I didn't claim that the study's findings mean that marijuana is harmful. What I am saying is that this study shows some evidence that it MAY be causing changes in the brain that might prove to be harmful. What galls me is that people immediately start blathering on about the study being "flawed" and that it is worthless. That's ridiculous. It is a preliminary study. The researchers have found some evidence that warrants further investigation. So what if the sample size is small? That simply means that another study with a larger sample needs to be initiated. Why don't you get right on it, since you are so concerned about it?

      April 19, 2014 at 17:31 | Report abuse |
    • John

      This "study" has been thoroughly and repeatedly debunked. http://www.huffingtonpost.com/2014/04/22/marijuana-brain-study_n_5170422.html?utm_hp_ref=politics&ir=Politics

      April 22, 2014 at 21:48 | Report abuse |
    • Fact Checker

      The Journal of Neuroscience has an article the states "These results provide evidence that the cannabinoid system can serve to protect the brain against neurodegeneration." Who ever wrote this review is a moron and a tool of the ignorant.

      April 24, 2014 at 14:30 | Report abuse |
    • theemptyone1

      No, it says that the study included people who smoked from one to eleven joints a week. I looked up the original paper and it says that the MRI findings of changes in brain structures was similar to those they see in schizophrenia.

      April 25, 2014 at 20:18 | Report abuse |
    • mical47

      I know from personal experience. I started smoking pot when I was fourteen. It was during my formative years. It suppressed my ambition, my drive and my goals for the life ahead. A potential achiever, I became nothing more than a dreamer. In essence, the most important part of my developmental life passed me by; the cognitive maturation of my mind. And so goes the poem.......... "Of all the words of tongue and pen, the saddest of these, "what might have been." ...... John Greenleaf

      May 12, 2014 at 15:17 | Report abuse |
    • Bannister

      Dude, I can tell that you're stoned! Your sentence makes no sense whatsoever!

      September 10, 2014 at 09:04 | Report abuse |
    • Coach Red

      This article reminds me of those that 'claim' GMO's are safe and wonderful and the ones that say 'Fracking is good for your state"!! So scary what you can pay people to say anymore. You cannot trust ANY "so called" scientific study.

      November 2, 2014 at 13:04 | Report abuse |
    • Coach Red

      Aaaaawww Mical47, need SOMETHING to blame for your lack of success in life? Try YOU dude, plain old YOU.

      November 2, 2014 at 13:06 | Report abuse |
  2. Jamie Lowell

    This study reflects nothing more than modern day "reefer madness" and has no real substance with which to rely- it doesn't even attempt a conclusion, it just suggests some kind of negative consequence. Meanwhile, there are substantive studies and a long term history of human use and several very well known, highly productive cannabis users (considerably more than the mere 19 or 20 used as the basis for this bogus study, that completely contradict the weak inference being provided. Shame on anyone accepting it as reality and shame on the mainstream media sources reporting on it as if it deserves to be recognized as valid.

    April 19, 2014 at 10:45 | Report abuse | Reply
    • Eeyore

      Where are these studies? Cite them. There is no "attempt at a conclusion" because it's a preliminary study. Can you provide anything other than anecdotes to back up your claims?

      April 19, 2014 at 11:12 | Report abuse |
    • theemptyone1

      In fact the original study paper says that the changes in brain structures in the study group that included people who smoked anywhere from one joint to 11 a week were similar to those they find in schizophrenia.

      April 25, 2014 at 20:15 | Report abuse |
    • cally

      theemptyone, I have seen your multiple comments stating that the researchers said that the changes were similar to those seen in schizophrenia, however, this isn't what was said at all. The only reference made to schizophrenia in the study discussion was an example given on how shape analyses can be a useful tool in research. This is in no way an implication that the observed differences in this study have anything to do with schizophrenia. Unless you can provide evidence that gives merit to what you are asserting to every commenter, please stop.

      May 18, 2016 at 18:33 | Report abuse |
  3. Eeyore

    As usual, a bunch of nincompoops who can barely read get on CNN, and find it necessary to display their ignorance for all to see. They don't like what the study shows because it contradicts their opinions (most of which are based on nothing but anecdotes and opinions with no basis in fact), they rant about how "flawed," "terrible," "misleading," etc. the study is. They have no studies that show that marijuana does not have any effect on brain function, but they're just SURE it can't be anything but beneficial. Or they're conspiracy theorists who are absolutely sure this is all rigged by "the man" who is anti-pot.

    You people are hilarious.

    April 19, 2014 at 11:34 | Report abuse | Reply
    • bartonizer

      Easy to generalize people you don't like as nincompoops. I think we can all agree that more research needs to be done on the subject. But many people- including those that don't consume MJ- have issues with making sweeping generalizations from a small study that relies on self-reporting, doesn't control for other variables, and is funded by organizations that benefit from its prohibition. Would you care to enlighten the rest of us simple folk with what the study actually tells us, and what we can extrapolate from such data?

      April 19, 2014 at 12:11 | Report abuse |
    • Jose79845

      People don't like it because it is based on politics and ideology instead of science and evidence.

      April 19, 2014 at 12:29 | Report abuse |
    • VitaminJ

      I found some of them studies you were asking people to cite regarding the positive effects of marijuana.


      Hope this helps!

      April 19, 2014 at 13:15 | Report abuse |
    • Eeyore

      Do any of your studies show that the effects that this study found DON'T occur? I didn't ask you for a study about the "positive effects of marijuana." I asked you to cite studies that show that the effects found in this one don't occur. Can you? Just because there are some effects that are positive does not mean that the effects this study found don't happen. Why don't you get that?

      April 19, 2014 at 17:25 | Report abuse |
    • Eeyore

      What evidence do you have that the study is "based on politics and ideology"?

      April 19, 2014 at 17:25 | Report abuse |
    • Josh

      Eeyore, it seems like you're calling anyone who has an opinion that differs from your a nincompoop. You haven't drawn a real point in any of your posts. It seems like you just don't like pot and you're trying to dismiss anyone who disgrees with the article.

      April 19, 2014 at 18:50 | Report abuse |
    • IJR

      Where in the study does it say "damage"?
      Why did they only use 40 people?
      Why didn't they check the brains when the study started?
      Are the findings actually negative?

      April 20, 2014 at 13:50 | Report abuse |
    • Anna

      Yep. I agree. What I find interesting is the claims of "Only 20 people-Really?!" As though that doesn't count. Or the "what a bogus study, it only includes this or that and not this and that" As though that matters. Perhaps some of these people who are picky about the study should do their own studies and post them online because that would actually count as a refutation. They also do not seem to understand studies one bit. It is not only hilarious, but rather sad-and revealing. Cognitive Dissonance.

      April 23, 2014 at 23:43 | Report abuse |
    • Fact Checker

      This study is rife with contradictions to the source material. It appears the the author of this review decided the cite the exact opposite of the findings that they supposedly "quote" here. The Journal of Neuroscience found "These results provide evidence that the cannabinoid system can serve to protect the brain against neurodegeneration." Yes the author is a parrot that is void of critical thinking let alone verifying their own work.

      April 24, 2014 at 14:39 | Report abuse |
    • theemptyone1

      While I agree that the CNN writers are pretty poor and hardly ever get a story right, they did the pot advocates a favor. Poor reporting/incomplete reporting helps the would be debunkers. However, I just looked up the original report and one finding that wasn't reported on here was that the changes they see in the brain are those they see in schizophrenic patients.

      April 25, 2014 at 20:12 | Report abuse |
  4. Jose79845

    The counseling industry backed a study to show why judges need to keep sending fresh meat to their counseling services, what a big surprise.

    April 19, 2014 at 12:24 | Report abuse | Reply
  5. groovecompany

    People who frequently consume marijuana drink a lot less alcohol than people who only occasionally enjoy it. Marijuana is a proven exit drug away from other substances, including alcohol.

    “In the present study, it has been shown that, in the Swedish general population, cannabis use is associated with a higher prevalence of other illicit drug use and hazardous alcohol use. Among cannabis users, frequent cannabis use is associated with a higher prevalence of other illicit drug use and a lower prevalence of hazardous alcohol use when compared to occasional cannabis use… The inverse relationship between the frequency of cannabis use and hazardous drinking has not been reported before to our knowledge… This may indicate that cannabis users and alcohol users are different groups, albeit with a high degree of overlap between groups, with different characteristics and clinical needs.”


    April 19, 2014 at 12:40 | Report abuse | Reply
    • theemptyone1

      Most people I have known of who smoked marijuana were not drinkers first. It never has seemed like a choice. In fact, many people who have never smoked cigarettes or drank alcohol very much are the actual marijuana users.

      April 25, 2014 at 20:08 | Report abuse |
  6. MeMe

    where is the study on alcohol?
    where is the study on prescription drugs?
    why target marijuana?
    and in other countries where marijuana is legal do they have any "studies"?

    April 19, 2014 at 13:09 | Report abuse | Reply
    • Eeyore

      There are plenty of studies on drugs and alcohol. Nobody's "targeting marijuana." It's a study.

      April 19, 2014 at 17:22 | Report abuse |
  7. Ilpalazzo

    It's funny how the study reports back with 'changes' and 'abnormal' and 'increase size' and the media immediately jumps on with the words 'damage' and 'bad'. So if it expands in size (hey btw, been living under a rock? They've been saying 'it expands your mind' ever since the 60s), would bigger brain be bad? I know a lot of people would want bigger muscles, bigger willies, etc, why is a bigger brain bad? Also, it only increased in size, no lesions or actual damage, guys.

    April 19, 2014 at 15:14 | Report abuse | Reply
    • Eeyore

      You really think "expanding your mind" means your brain gets bigger?

      April 19, 2014 at 17:21 | Report abuse |
    • theemptyone1

      The undercurrent of pot using "true believers" is unmistakeable in your comments as many here. There are separate studies about those things. In this case, the subject is how the brain changes. I grew up in the Sixties and I used a bit and I also worked at a famous free clinic helping people who used many substances. I also have an advanced degree in health care that includes neurophysiology. First, marijuana may be fun, but it also is well known to make most people lazy and drops their intelligence and harms at least short term memory in the short term. I think it also causes mental problems for many people the habitual state of denial of deficiencies being a big one, but depression, paranoia and some types of obsessive neurosis as well. This is not to mention weight gain and life and career stagnation. Interestingly, alcohol seems to generally actually propel people, at least up to a point, until they drink too much as a habit. As far as harm to families, spouses, etc., I think marijuana does more harm over a longer period of time and its increased use in our society since the 1960s has resulted in worse family structure and more irresponsibility over all than in alcohol dominant centuries before it. Just look at any culture where marijuana has been used for a long time. What you see is squalor and overwhelming poverty. I have had mechanics that use pot and even dealt with attorneys that used. I'd say that pot usually causes a poor performance no matter what you're doing. Only arguing emotionally seems to gain ground. But not with people who know their stuff. More just to themselves and others like them.

      But this study finds that brains change in structure. That is always a worrying thing because unnatural changes (i.e. not due to normal expression of one's dna) is a precursor to neoplastic changes. Remember how Bob Marley died of brain cancer? How many joints did he smoke a day? But if the area for emotional response enlarges, it may affect how one responds to stimuli, even suppressing other otherwise normal functions through actual overriding of the neural synapses.

      There are many pharmaceuticals that do certain things and very few of them make the affect without some side effects. The discussion always has been whether the potential harm is worth the perceived benefit. In the case of recreational pot, the user is trading some harm for a high. Realizing this is being realistic. Talking about how bad other substances are doesn't make using marijuana better than it is. Try doing activities that produce a "natural high," like hiking and smelling the flowers in spring, or even some adrenalin sports if you're young and fit. Attaining new knowledge is a kind of high, too. Satisfying curiosity is a great high, if you're truly self-directed. I submit that smoking pot, like all the rest of the stuff is what it always was, an escape from reality, a cop-out.

      April 25, 2014 at 19:41 | Report abuse |
    • theemptyone1

      I read the original paper and it says that the changes seen in the MRI studies of the pot users were similar to those seen in schizophrenia.

      April 25, 2014 at 20:21 | Report abuse |
  8. stel1776

    Of course they conveniently leave out a few details. For one the 'abnormalities ' they found in the cannabis users were two areas of the brain with greater size and neural density. This usually is not a bad thing. They also never claimed that cannabis caused this. If we are going to discuss popular substances which have an adverse effect on the brain, it would make much more sense to talk about alcohol, which has been proven to cause brain damage. Cannabis on the other hand, despite decades of study has not been shown to cause brain damage in adult users. In fact, the U.S. government has a patent on the cannabinoids found in cannabis for protecting the brain:

    "This new found property makes cannabinoids useful in the treatment and prophylaxis of wide variety of oxidation associated diseases, such as ischemic, age-related, inflammatory and autoimmune diseases. The cannabinoids are found to have particular application as neuroprotectants, for example in limiting neurological damage following ischemic insults, such as stroke and trauma, or in the treatment of neurodegenerative diseases, such as Alzheimer's disease, Parkinson's disease and HIV dementia."
    Patent 6630507 – Cannabinoids as antioxidants and neuroprotectants. Filing date: Apr 21, 1999.

    April 19, 2014 at 16:40 | Report abuse | Reply
    • theemptyone1

      What?! Changes in the brain that aren't genetically driven are potentially very dangerous. A neoplasm is a new growth in the brain and sometimes they become cancerous. If you have a part of the brain that grows in size, it could easily cause horrible headaches (migranes). If one brain function becomes exaggerated, couldn't that suppress other functions by overwhelming the synapse of other neural tracts? I have an education in neurophysiology and I can see the dangers in a moment.

      You children are going to have to realize that marijuana using is going to have some risks. It doesn't matter that other substances do too.

      April 25, 2014 at 19:46 | Report abuse |
    • theemptyone1

      Also, the claims you are making about ischemia and such are ridiculous on their face. Pot smoking increases CO2 in the lungs and blood stream. There is no way in H that this could result in reducing ischemia or do anything but harm the circulation and heart. I just read an article about how marijuana causes those very problems, in fact.

      April 25, 2014 at 19:50 | Report abuse |
  9. Greeshma

    Eeyore & FamilyDoc2 – U BOTH ARE TRULY RIDICULOUS!!!!!!!

    April 20, 2014 at 03:36 | Report abuse | Reply
  10. Kevin Hunt

    The headline of this article is misleading.
    A teen who consumes alcohol is likely to have reduced brain tissue health, but a teen who uses marijuana is not, according to a new study.

    “Researchers scanned the brains of 92 adolescents, ages 16 to 20, before and after an 18-month period. During that year and a half, half of the teens - who already had extensive alcohol and marijuana-use histories - continued to use marijuana and alcohol in varying amounts. The other half abstained or kept consumption minimal, as they had throughout adolescence.

    However, the level of marijuana use - up to nine times a week during the 18 months - was not linked to a change in brain tissue health.
    The study was conducted by researchers at UC San Diego and was published in the April issue of the journal Alcoholism: Clinical & Experimental Research.”

    April 20, 2014 at 10:48 | Report abuse | Reply
  11. GoodGrief

    "Don't do it early–prior to age 16. That's what our data suggests, that regular use of marijuana prior to age 16 is associated with greater difficulty of tasks requiring judgment, planning and inhibitory function as well as changes in brain function and white matter microstructure relative to those who start later." Excuse me but none of the subjects were younger than 18. How can her data have anything to say about use prior to that? I smell a rat

    April 20, 2014 at 11:45 | Report abuse | Reply
  12. Yahshva

    That is funny, I read the entire report and not one word was said about "Brain Damage".

    But it did say things like:

    "Both gray matter density and average volume were increased in marijuana participants..."

    Sounds to me like the "abnormalities" they talk about may indeed be good abnormalities.

    According to this study, they couldn't really tell if the causation was marijuana according to the following excerpt:

    "Because this is a cross-sectional study, causation cannot be determined...Early exposure to alcohol may have
    also affected brain structure"

    So with the above information we learn that the entire study was a sham, and a waste of time.

    What I notice is that I have read the entire report and not one word was ever spoken about "Brain Damage" yet the news agencies just pile it on.

    Sheeple work at its finest.
    Actually Marijuana is mentioned in the bible by name:

    1980, etymologists at Hebrew University in Jerusalem confirmed that cannabis is mentioned in the Bible by name, Kineboisin (Also spelled Kannabosm), in a list of measured ingredients for "an oil of holy ointment, an ointment compounded after the art of apothecary to be smeared on the head. The word was mistranslated in King James version as `calamus' – Exodus 30:23 (Latimer 1988).

    The above means it was in the oil they used to rub on their skin, it was in the bread they ate called the Lord's Supper, and it was in the incense that was burned in the temples.

    Marijuana is the Tree-Of-Life talked about in the bible, indeed it was a real tree that grew from the ground:

    Gen 2:9 And out of the ground made the LORD God to grow every tree, the tree of life was also growing in the garden...

    The above reveals that the Tree-Of-Life is indeed a real tree that grows in the ground.

    Rev 22:2 In the middle of its street, and on either side of the ocean, was the tree of life. The foliage of the tree are for the healing of the nations.

    We are living in a day when the Tree-Of-Life (what the world calls marijuana) is healing everything it comes in contact with.

    The ONLY thing dangerous about marijuana are the cops who shoot people for having it:

    Number of American deaths per year that result directly or primarily from the following selected causes nationwide, according to World Almanacs, Life Insurance Actuarial (death) Rates, and the last 20 years of U.S. Surgeon Generals' reports.

    TOBACCO – 340,000 to 450,000

    ALCOHOL (Not including 50% of all highway deaths and 65% of all murders) – 150,000+

    ASPIRIN (Including deliberate overdose) – 180 to 1,000+

    CAFFEINE (From stress, ulcers, and triggering irregular heartbeats, etc.) – 1,000 to 10,000

    "LEGAL" DRUG OVERDOSE (Deliberate or accidental) from legal, prescribed or patent medicines and/or mixing with alcohol – e.g. Valium/alcohol – 14,000 to 27,000

    ILLICIT DRUG OVERDOSE – (Deliberate or accidental) from all illegal drugs – 3,800 to 5,200


    (**Marijuana users also have the same or LOWER incidence of murders and highway deaths and accidents than the general NON-marijuana using population as a whole.** Cancer Study, UCLA; U.S. Funded ($6 million), First & Second Jamaican Studies, 1968 to 1974; Costa Rican Studies, 1980 to 1982; et al. LOWEST TOXICITY 100% of the studies done at dozens of American universities and research facilities show pot toxicity does not exist. Medical history does not record anyone dying from an overdose of marijuana (UCLA, Harvard, Temple, etc.)

    Accordingly a 1993 study done by the U.S. Department of Transportation came to the same conclusion as the above concerning marijuana and driving safety:

    “Marijuana, administered in a dose of 100 µg THC per kg of whole body weight...did not significantly change mean driving performance as measured...” – U.S Department of Transportation: Marijuana and Actual Driving Performance DOT HS 808 078

    The fact is people who use marijuana reflexes are not affected in a negative way and they become more conscious of safety, sometimes refusing to even drive.

    Marijuana is a plant with a safety record second to none.

    Anyone who would like to dispute these FACTS, point to a credible death that involves marijuana and nothing but marijuana, or hold your tongue.

    April 20, 2014 at 12:30 | Report abuse | Reply
  13. IJR

    Where in the study does it say damage?
    The study is a joke. 40 people is a ridiculously small sample size.
    They did not check the brains when the study began.
    They do not say if the changes in the brain are positive in nature.

    April 20, 2014 at 13:47 | Report abuse | Reply
  14. Benson

    I cannot fathom the necessity to back marijuana in a sense of recreational use, as well as any other manipulating drugs. Pity for those who barely function without.

    April 20, 2014 at 16:30 | Report abuse | Reply
  15. John g

    How people can continue to believe that marihuana use is not harmful to the brain is incomprehensible to me I've seen too many young people destroy their motivation

    April 21, 2014 at 07:58 | Report abuse | Reply
  16. Joe

    Study does not take in other factors of lifestyle and economic status. In addition, some people have low IQ and low motivation and then start to smoke. People with higher IQs are less likely to even be in the study or admit to smoking, because they have more to lose. Check your IQ and the people who did the study, because we arent foolish enough to take the science with your predetermined interpretation of statistics.

    April 21, 2014 at 08:28 | Report abuse | Reply
  17. Ashkan

    I have heard that weed causes less harm to human body than cigarette does. is this right?

    April 21, 2014 at 09:00 | Report abuse | Reply
  18. marc

    no worse than alcohol
    and alcohol is legal

    April 21, 2014 at 17:09 | Report abuse | Reply
  19. Kyle McMullen

    Cannabis promotes embryonic and adult hippocampus neurogenesis.

    J Clin Invest. 2005;115(11):3104–3116. doi:10.1172/JCI25509.

    April 21, 2014 at 17:48 | Report abuse | Reply
  20. Jrad

    The question is: are these changes good, bad, or do they even make a difference? IQ is a pretty crappy measure of intelligence anyway.

    Regardless, the way these researchers are framing it, I'm sure their conclusion will be something along the lines that smoking marijuana is worse than drinking bleach.

    April 21, 2014 at 17:56 | Report abuse | Reply
  21. beastmc

    in ANY study...in a controlled environment with specifc variables, you can easily dictate the findings to lean towards the bias answer you looking for.

    April 21, 2014 at 18:18 | Report abuse | Reply
  22. BrainDoc

    @NERVANALC Twitter feed by board certified neurologist regarding marijuana. I completely disagree with the conclusions put forth by my colleagues. Marijuana is beneficial to the brain and its usage should be promoted. Seeking to loosely associate harm with non-specific brain findings in a very small patient sample size completely undermines this researchers perceived expertise. If unbiased discussion is allowed the tome of available data dictates we promote daily marijuana usage for preventative brain health maintenance and therapeutic usage for most neurologic disease. Those of us in the neurologic community whom continue to ignore the factual neuronal protective properties of this therapy will eventually be antique. Get on board now colleagues, this is a huge advancement waiting to happen for nervous system health with actual disease modifying activity.

    April 21, 2014 at 21:08 | Report abuse | Reply
  23. Hercamus Flaviode

    It gives me great pleasure to see the many measured and testing perspectives taken on reviewing and considering this study and article. I read it and thought – there is NO specific findings listed in this article at all. It smells like a hack job. I read your comments and you folks have delivered so much awesome commentary, research and critical thinking – I was thrilled to know that there are folks like you out there. Thank you! CNN seems to post puffery without half of your journalistic integrity.

    April 21, 2014 at 21:11 | Report abuse | Reply
  24. klark

    112 of anything a week booze. pain killers ,aspirn,candy bars,are gonna mess your whole body up and out of all those I mentioned mj is the only one ive actually seen save lives so get real

    April 22, 2014 at 14:36 | Report abuse | Reply
  25. Cade

    Just an idea, what if people who have mental illness/predisposed are more likely to smoke pot because they care or think less about their health. Healthier and balanced individuals are scared to smoke it because they care about their health. Now if marijuana did nothing at all, one would come to the conclusion marijuana caused those problems, even though people with mental illness already had it. Also i feel like most of the people saying they were never the same again, were the ones also huffing paint, but think all drugs do equal damage lol.

    April 22, 2014 at 16:41 | Report abuse | Reply
    • theemptyone1

      Well, you're on the right track, but different substances cause different effects in different areas, so they're not equal. But abuse is abuse and if you're using something to get high, then you're taking more than your body can metabolize at the time and that is the definition of toxicity and therefore it's abuse. I'll personally take the light buzz I get from an extra glass of wine than the foggy hang-over that pot leaves you with for a day or two afterward. But I read the original article on this study and it says that the changes seen in the MRIs of the user group was similar to those they see in schizophrenia.

      April 25, 2014 at 20:26 | Report abuse |
  26. Diane

    The way this entire article is a play in words! Says abnormalities when smoking wow you dont say... There are also similar abnormalities when we drink or eat cold foods and beverages .. Also just about everything kills brain cells but they never mention brains cells naturally die and regenerate as well 🙂 nor do they mention the the same building blocks we are giving in breast milk are also found in marijuana! Nor does this article includes recent studies that marijuana cures certain forms of cancer!!
    Please stop writing everything off as bad or damaging if
    1. You do not have proper studies done 2. Someone told you its "bad".
    3. Youre just plain assuming it because you dont do it.

    April 22, 2014 at 17:00 | Report abuse | Reply
  27. Ben Hayman


    a damning report on this paper and the scientists involved.

    April 22, 2014 at 18:46 | Report abuse | Reply
  28. MrBadgerToYou

    This is a day late and a dollar short. For whatever reason the powers that be have not allowed much if any study of marijuana for the past 40 years or so. So people have formed their own opinions from anecdotal evidence. We all know people who have been puffing leaf for decades and nothing really happens to them.

    So please, shut up with your late studies.

    April 23, 2014 at 09:14 | Report abuse | Reply
    • Eeyore

      Why? Are you bothered by the findings because they don't jibe with your beliefs? Why shouldn't marijuana use and its effects be the subject of research?

      Afraid they might find out it's not as beneficial and harmless as you'd like to think it is?


      April 23, 2014 at 09:24 | Report abuse |
  29. Rich McCracken

    The study doesn't say what the mainstream news has reported it to say. One of the study's two lead scientists:

    "I think I saw one headline that was 'Marijuana reshapes the brain' and I groaned — that's not what we did," said Dr. Jodi Gilman, 31, author of the now-famous Harvard Medical School/Massachusetts General Hospital study on marijuana's effects, in an interview with PolicyMic.

    I analyze the study and easily prove that the study's data proves the opposite of what they meant to prove.


    April 24, 2014 at 00:20 | Report abuse | Reply
  30. Sylvia Taylor

    Oh, really?! And what does the "study" reveal about alcohoil deaths and marijuana deaths? Alcolhol violence vs marijuana violence. Child and spouse abuse using alcohol vs same abuse using marijuana? I dare say these "studies" and the people that report them are really getting out of hand.

    April 24, 2014 at 14:07 | Report abuse | Reply
    • theemptyone1

      Still, I'd much rather have my car worked on, or my legal case presented by someone who got drunk the night before than someone who got high on pot the night before.

      April 25, 2014 at 19:57 | Report abuse |
  31. Andrew

    I really dont see why this one negative thing, among several others, has to pretend to be such a terrible thing. This article is very broad on what exactly is "brain damaging". 40 people is an incredibly small percentage of people. Mentally marijuana has only been thought of to worsen diseases like Bi-Polar disorder and schizophrenia. How can people like Bill Clinton, Barrack Obama, Willie Nelson, and any older former/current smoker be where they are today if these "brain damaging" effects were actually that serious. I have had several concussions and that puts me at more of a risk for depression, bi-polar disorder, Alzheimer's, and many other mental disorders. As far as I know marijuana cannot do any of that, its even been known to help depression and possibly help prevent Alzheimer's. How could doctors like Dr. Sanjay Gupta go on CNN, this same news network, and endorse a plant that would cause any real harm. There are tons of small scale studies like this. If I hand you two apples on or both might be bruised. If I scan the brains' of two stoners they might have abnormalities.

    April 26, 2014 at 00:53 | Report abuse | Reply
  32. mike smith

    This study has been completely DISPROVEN:


    I'd say that CNN should know better but that's why I don't trust them to begin with.

    April 26, 2014 at 20:00 | Report abuse | Reply
    • Eeyore

      You don't know anything about science, do you?

      April 28, 2014 at 22:50 | Report abuse |
  33. edlf2014

    Marijuana user's brains may have been damaged before they began. Maybe like the chicken and the egg.

    April 28, 2014 at 21:50 | Report abuse | Reply
  34. CRobin

    I always thought of Eeyore as a donkey, not a troll.

    May 1, 2014 at 21:21 | Report abuse | Reply
    • Eeyore

      You can call me whatever you want. But when someone calls BS on a study, then he or she ought to be able to explain what's wrong with the study.

      May 1, 2014 at 23:15 | Report abuse |
  35. Krymsun

    No, this study doesn't show marijuana wrecks your brain

    How Bad Is Marijuana for Your Health? What recent press coverage gets wrong.
    "Reporters overstated the findings, mischaracterized the study, and failed to mention previous research done on pot smoking and health."
    A press release from the Society for Neuroscience trumpeted the Gilman study’s importance because it looked at casual users rather than regular pot smokers, who form the basis of most marijuana studies. That claim is dubious in the extreme. The subjects averaged 3.83 days of smoking and 11.2 total joints per week. Characterizing these people as casual pot smokers was a great media hook, but it defied common sense.. Just two years ago, for example, Janna Cousijn and colleagues published a study on a group that she called “heavy” marijuana users. In the average week, they smoked 3 grams of cannabis – approximately 2 grams less than Gilman’s casual smokers.

    How a Marijuana Study Can Poke Holes in Your Brain
    "The main problems with the study, according to people who have pushed back, is its small sample size (20 college students), its definition of “casual” (the average study participant smoked 11 joints a week), the fact that most of the weed smokers were also drinkers, and the fact that only one MRI scan was done for each participant, which is not ideal."
    Lior Pachter, a University of California, Berkeley computational biologist, has done what is most likely the most thorough review of the paper, and concluded by calling it "quite possibly the worst paper I've read all year."
    Jacob Sullum wrote a piece for Reason called “Study of Pot Smokers’ Brains Shows that MRIs Cause Bad Science Reporting.” But Sullum also misses the mark a bit. MRIs and studies like this don’t cause bad science reporting; misleading sources cause bad stories. And correlation not equaling causation is a cardinal rule of science – one that was missed here – but so is bad data in, bad data out.

    May 1, 2014 at 22:00 | Report abuse | Reply
  36. J123

    Here is an article about underage drinking.


    So – beat up on pot BUT – kids have been boozing for decades.....

    May 12, 2014 at 18:51 | Report abuse | Reply
  37. Tam

    I could be part of a study. I grew up with good grades in school, B's and above usually (wasn't very good at history until college). I was involved in sports my whole life. Track & Field, swim team, softball. I excelled at math and science. I married by the time I was 20, had 4 children by the time I was 27. All healthy. Continued my education throughout those years. I've always had a job of a clerical nature up to manager level. I've never liked alcohol. (mostly the taste and the dizzy feel from the affects) I have never had a moving violation ticket, or any other mischief with the law. I have raised those 4 children into fine adults, and now I am a grandmother 4 times over. I still work. I still stay active. I still earn and save money just like everyone else. However, I have smoked marijuana since I was in my early teens. I have not suffered a stroke. I don't shy away from tasks. I don't forget to do things. I don't go out and commit crimes if I run out of marijuana. What I am saying, is that everyone is different and just by testing a few out of thousands won't get you the answers you seek. Arguing with each other won't help you figure out who's right or wrong. No one is right or wrong, they are just different. I've been "drunk" before and "high" before. I can't function when I am drunk. I can't form words right, I can't see straight, definitely can't drive. When I am "high". I can do all of those things and complex math problems too. So, short of "all smoking is bad on the lungs", I don't believe THC is that bad. just my input.

    May 31, 2014 at 08:04 | Report abuse | Reply
  38. Jake

    Really? How many times does this have to be proven wrong? And don‘t say "Oh, they just did". All of these news outlets are just trying to make people afraid of cannibis. Cannibis has shown its self to have a huge number of health benefits. Just to list a few(and you can look this up yourself too) a cure for over 5 cancers, kills brain tumors, stimulates the growth of brain cells, painkiller, and anti-anxiety. Again, if it sounds to far fetched, do your research. Oh, one of my favorite qoutes, A NEW STUDY SAYS, WE CAN MAKE YOU BELIEVE ANYTHING BY SAYING A NEW STUDY.

    June 7, 2014 at 11:24 | Report abuse | Reply
  39. mother

    As a mom of a child who has smoked since she was 13,I have to say she's a 4.0 honor student in her senior year of college. Her goals are very high and she will be getting her doctorate in behavioral science.. I will add I didn't know until she was 18 that she was smoking.
    It doesn't always make you a couch potato with no goals.

    June 10, 2014 at 09:01 | Report abuse | Reply
  40. oneillsg7

    Is it me or did Fox News write this article?

    "According to the National Survey on Drug Use and Health, in 2012 nearly 19 million Americans used marijuana. It's the most-used illegal drug in the country and use is increasing among teenagers and young adults."

    You mean illegal in 48 of 50 states?

    Brain scans mean almost nothing, especially in an area of the brain that very little is unknown about, such as the amygdala. This article is a joke.

    June 11, 2014 at 17:15 | Report abuse | Reply
  41. bunny

    as the mother of a 19 year old son who is ADDICTED to marijuana. i can tell you 1st hand it is ruining our lives. we have tried everything in our power to help him and advise him. he has become violent , threatening, spiteful, secretive and his memory has become so distorted. in the UK our children are classified as adults at the age of 18, so our hands are tied in what we can do to show him what's happening. he has told us to our faces family means nothing to him.i wish for once someone would stand up and say yes it's addictive! i's OK for people to have there opinion but until you have walked in the shoes of a family member. you can not imagine how awful it is. my son grew up in a loving home with a large family and safety net. There were no traumatic events so no excuses

    June 25, 2014 at 05:39 | Report abuse | Reply
  42. guest

    Once you start comparing smoking marijuana to smoking cigarettes, drinking alcohol etc. you have already lost the argument. Smoking ANYTHING is harmful, you are burning a substance and putting it into your lungs. Smoke is ALWAYS unhealthy. It's not rocket science.

    As for the brain matter, I've known of individuals that have had brain cancer, all pot smokers/ingesters...but let's legalize it over the entire U.S. to get this rebellion out of the childrens system so they can see how truly bad it is, like people had to learn with smoking after it was glamorized in the 50s. Their life, their right to destroy their bodies, everyone eats processed garbage anyhow. Time will tell.

    July 19, 2014 at 08:47 | Report abuse | Reply
  43. DG Futurist

    Wrote Ten Startling New Facts About Brain Damage and Marijuana after a decade of study as a scientist. I could hardly keep them in stock, and they were read so many times in book stores that they became too durty to sell. Most people who bought book realized that hash smokers in Middle East ARE brain damaged and it isn't their drinking water. It is smoking a substance with over 403 substances in it that makes it like alcohol and alcohol that are both dangerous to growing brains

    August 19, 2014 at 18:31 | Report abuse | Reply
  44. Bob


    The roots of the marijuana-kills-brain-cells myth are deep despite the lack of credible evidence. The original study supporting this notion is questionable at best and recent research suggests exactly the opposite.

    In 2005, a study showed cannabinoids' ability to promote neurogenesis in the adult hippocampus, the brain region responsible for many important brain functions including mood and memory. The authors also cited anti-anxiety and anti-depressant effects that accompany the neurogenesis. This explains why people across California, Colorado, Washington and other marijuana-friendly states often turn to the herb for a mood-boost instead of pharmaceutical drugs. It also supports research that marijuana helps improve cognitive function in bipolar disorder patients. This brings us to our next fact....

    September 4, 2014 at 16:35 | Report abuse | Reply
    • Coach Red

      Anti-MJ groups will try ANYTHING to continue the propaganda. OMG I even saw one article where a SCIENTIST stated that you hallucinate from MJ!! A SCIENTIST!! The pharmaceutical industry has some VERY VERY deep pockets! They have bought out many politicians already and continue with organizations that people tend to listen to because they USED to be there for the citizens, but not any longer. If the world were to discover how damaging pharmaceuticals are compared to MJ and how many things can be alleviated with the use of MJ WITHOUT all of the side-effects and MORE pharmaceuticals needed to help with the side-effects, the pharm companies would SHRINK immeasurably and they know it. THIS has them scared. You will really see them come out of the woodwork with 'studies' now, their livelihood is at stake!

      November 2, 2014 at 13:13 | Report abuse |
  45. John Doe

    How do they get stats about the regular use of marijuana prior to age 16? Clearly it would be illegal to subject minors smoke, and do you think any minor who isn't an absolute idiot to begin with would admit to smoking on even a weekly basis?

    September 4, 2014 at 19:25 | Report abuse | Reply
  46. Stacey

    Is it difficult to study a person for 90 days without smoking pot and then study them for another 90 days smoking pot? Why study someone that doesn't smoke pot? I don't get that.

    October 4, 2014 at 09:53 | Report abuse | Reply
  47. Peter


    This 2001 study says that marijuana does not affect performance on cognitive tasks related to intelligence...but it could affect different areas of the brain differently. Some people might be sensitive to drugs that affect the CNS but it could also be attributed to different factors both related to and independent of the marijuana.

    I used to smoke marihuana habitually and I felt as though it did cause minor cognitive impairments...but I also think it causes a great deal of anxiety because it makes you aware of things you would not otherwise notice. On top of that, I think it can reduce motivation and energy in the long run. What's better than sitting in front of the TV and binge watching Southpark stoned out of your mind?

    October 9, 2014 at 11:06 | Report abuse | Reply
  48. Noelle Silva

    Yeah maan....joints. It'd doubt they'd find any problem if they switched it to smoking out of a pipe!

    November 10, 2014 at 23:14 | Report abuse | Reply
  49. serkeara

    recent research from The University of Texas have shown that the weed likely to reduce grey matter in brain cells which related to addiction, but it also shown that these reduction didn't effect user capabilities. Moreover, weed also enhance brain connectivity.I suggest you to read this research for your information: http://prescriptionfact.com/does-weed-kill-brain-cells/

    December 12, 2014 at 10:02 | Report abuse | Reply
  50. Fatman420

    Who smokes joints anymore?

    January 1, 2015 at 06:58 | Report abuse | Reply
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