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. David Sherefkin

    There is no merit to the headline of this article ,No links to the study have been made available.
    This is a typical example of the insatiable need to publish quickly rather then accurately ,
    Articles like this one only help to reinforce ignorance and sub-critical thinking ,
    Marijuana has an effect on the brain just like cigarettes & chocolates do , so what is the argument ?
    What are the exact negative effects on the brain ? Lower IQ ? and that claim is based on what research ?

    April 16, 2014 at 09:23 | Report abuse | Reply
    • lukemace1

      I was about to post the same exact thing, good old CNN propaganda for us. It bothers me that they are that ignorant to have a generic interview in the first stage of testing, and they just assume for us that it is "damage". What if it helps us cope better emotionally?

      April 16, 2014 at 09:48 | Report abuse |
    • sm5574

      There is a link to the study in the second paragraph. I will not speculate as to why you may have missed it.

      April 16, 2014 at 10:12 | Report abuse |
    • stupid

      Studies have also shown that reading books a lot can cause "their brains rewire and new connections are formed".

      So that must be a bad thing right?

      April 16, 2014 at 10:13 | Report abuse |
    • steve

      Important – Did they wait for the effects of the marijanua to leave the blood stream or where they still partially stoned?

      April 16, 2014 at 10:15 | Report abuse |
    • steve

      Ok, read the study, they only refrained the day of the study for the effects to leave, thats not enough. Should give them a couple days.

      April 16, 2014 at 10:18 | Report abuse |
    • Chuck

      This is a news site, not a science journal. Be realistic about your expectations.

      April 16, 2014 at 10:24 | Report abuse |
    • mapedog1

      RIght? I marijuana reduces anxiety, and anxiety impedes mental function, you are improving function through usage. I like that they just throw strokes in there. Smoking raises blood pressure, which can lead to strokes. Throw anything that raises blood pressure onto the list then.; skydivers are all headed for strokes I guess.

      April 16, 2014 at 10:46 | Report abuse |
    • areyousaying

      Spot on. What are these "abnormalities" Are they worse than those from consumin he more dangerous, more addictive, Jesus and lobbyis approved harder drug alcohol?

      Did the big alcohol lobby buy off the results.

      April 16, 2014 at 10:53 | Report abuse |
    • Bob

      I think the study author, the "journalist" who wrote the article and the readers are all high.

      April 16, 2014 at 10:56 | Report abuse |
    • Bill K

      First, what about the changes to your body from alcohol use? And who funded this study? It just seems that when you see articles like this, there is an agenda hidden in there somewhere.

      April 16, 2014 at 10:57 | Report abuse |
    • Weston

      I smoked pot for 9 years from the age of 16-25. I wish I could say I felt no changes to my brain, but that's not true. I DO believe my IQ is lower now than it was back then. I have had vascular problems (though not a stroke), I also have two uncles in their 50s who have smoked pot their entire adult lives and I have no doubt whatsoever that their severe mental issues (One is a diagnosed schizophrenic) are directly related to their pot use.

      The one thing you can guarantee about pot users, is that 95% are completely dishonest about there pot use and how it affects them. Thing is, due to THC's fat solubility, the long term effects happen too slowly for the pot user to be aware of. I know that's how it was for me, and no one can tell me otherwise.

      I commend those doing this work. One day when these users stop using and get honest with themselves they might begin to appreciate a better understanding of what they did to themselves.

      April 16, 2014 at 11:07 | Report abuse |
    • Bill K

      Just look at how the main article was written. It is full of "I think", "He said", and so on. This is not the kind of article that I would ever put much credence in. Not very scientific at all.

      April 16, 2014 at 11:13 | Report abuse |
    • Paul

      The key point is the following quote from the article:

      "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."

      Thus the conclusion "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" is irrational and ridiculous since no negative effects were found. Funding for scientific research should be limited to people capable of putting aside their biases and thinking rationally.

      April 16, 2014 at 12:16 | Report abuse |
  2. NameOrder

    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.

    That is the only line in the whole article that should concern anyone with a brain and who cares about civil liberties. Obviously the good Dr. is getting some slack from the big Pharm bill payers. Just before the BIG 420 Holiday. Great article Dr.

    April 16, 2014 at 09:32 | Report abuse | Reply
    • The REAL Truth...

      Perhaps they should now repeat the study, and replace pot with alcohol and then COMPARE the results.. should be very interesting.. I'd bet the 2nd study shows more DETRIMENTAL effects from alcohol.

      April 16, 2014 at 10:59 | Report abuse |
  3. Michael, Chapel Hill

    Opinions expressed by US experts are highly biased.So is the case with marijuana. You can find some expert somewhere who may tell that marijuana is good. However, many scientists in various parts of the world has found that marijuana use can trigger lots of medical problems.

    April 16, 2014 at 09:48 | Report abuse | Reply
    • zack

      so does a mcdouble and a large fry and coke. Are those illegal? Do i need to get a card from my doctor to get my dose of fat grease? Hell no .99 cent and you got yourself a heart attack.

      April 16, 2014 at 10:07 | Report abuse |
    • Raul

      Citation please. (Just because you say it doesn't make it true. (Darn interwebs...))

      April 16, 2014 at 10:28 | Report abuse |
    • helicohunter

      Clearly, you don't know how science works in the U.S. Research on Marijuana is not funded by drug companies. Most research is funded by the NIH, and there is NO pressure to get results that favor one conclusion vs. another. University scientists are paid to find the truth. If they fabricate data, they lose their careers. If they misinterpret data, it will be caught be journal reviewers or other scientists. The Journal of Neuroscience is a respectable journal. You can bet that their methods and results were scrutinized by other researchers who don't have skin in the game.

      April 16, 2014 at 11:11 | Report abuse |
  4. Sam R.

    1. Who smokes joints any more?
    2. So glad money is being spent on useless studies like this, maybe try looking into something that is actually harmful and stop publishing this garbage for the press you'll get from the contrarian "results."

    April 16, 2014 at 09:49 | Report abuse | Reply
  5. JuneBug

    Aging has been incontrovertibly demonstrated to be related to change in brain structure. Lets ban it.

    April 16, 2014 at 09:58 | Report abuse | Reply
  6. zack

    lol people that believe this are just ignorant. Its a fact that alcohol and cigs are way worse and ADDICTIVE. But thats alright. If we could easily grow tobacco and make alcohol in our basements they would be illegal too cuz the gov couldnt make money off it. Also funny that weed is LEGAL in our nations capital.

    April 16, 2014 at 10:03 | Report abuse | Reply
    • Dylankoufax

      Zack, pot is legal in Washington State, not D.C. Those are two completely different places.

      April 16, 2014 at 10:13 | Report abuse |
    • Tom

      And do you need more proof that marijuana is damaging to your brain than the capital of this country?

      April 16, 2014 at 10:17 | Report abuse |
    • zack

      you're right they are two completely different places. Thats the only thing you're right about. Look up the pot laws for dc. And next time know what your talking about.

      April 16, 2014 at 10:28 | Report abuse |
    • Fred Evil

      Actually medical marijuana is legal in DC.

      April 16, 2014 at 10:29 | Report abuse |
    • zack

      you cannot be arrested for possession up to an ounce in dc. its a $25 dollar fine which is just another scam. ill give you the benefit of the doubt, the law hasn't taken affect yet i don't believe.

      April 16, 2014 at 10:37 | Report abuse |
    • zack

      Its "decriminalized" not "legal".. in other words its a chevy silverado not a gmc sierra.

      April 16, 2014 at 10:39 | Report abuse |
    • helicohunter

      Your comparisons are irrelevant. This isn't about what is more addictive. Different drugs have different effects on the body. Cigarettes are very damaging to the lungs and blood vessels, but don't alter brain structure. Alcohol is damaging to the liver. It definitely affects brain function, but doesn't alter brain structure. Claiming that marijuana can't hurt the brain or body just because other substances also hurt the brain or body is a stupid argument. That's like saying that meth must be safe because heroine is known to be unsafe.

      April 16, 2014 at 11:19 | Report abuse |
  7. John

    "Casual marijuana use may damage your brain" What's your point? Alcohol use is PROVEN to cause brain, and liver damage..

    April 16, 2014 at 10:07 | Report abuse | Reply
  8. michael de rigueur

    Noncents, I'ev ben smokig far yers an I fine

    April 16, 2014 at 10:08 | Report abuse | Reply
    • Phil Costastine

      Classic, made me laugh out loud!

      April 16, 2014 at 10:27 | Report abuse |
    • Krstl


      April 16, 2014 at 10:51 | Report abuse |
  9. johnsonJohnson

    This article brought to you by every major pharmaceutical company that has something to lose. Please keep taking our harmful drugs that cost 300% higher than pot. Then take another one of our drugs to counter the harmful side effects the first drug causes!

    Big Pharm

    April 16, 2014 at 10:10 | Report abuse | Reply
    • Chuck

      Casual pot smokers and medical pot are not the same quality nor is there any causal and significant reason for casual pot smoking. So what is your point?

      April 16, 2014 at 10:28 | Report abuse |
    • Timmy Suckle

      I kissed my way up to CEO at a health insurance company. Now I take over $1,000,000 of your health care dollars for NO VALUE ADDED to your health care. And that’s just me. Now think about how many other CEOs, VPs, Directors, Managers, etc. are at my company alone. Now multiply that by thousands of others at hundreds of other health insurance companies. From 10 to 25% of your health care dollars go towards administration that adds NO VALUE to your health care. But my company’s PAC dollars will continue to fool you little people into thinking that a single payer system will be bad. Little people like you are so easy to fool. Little people also don’t realize that a single payer system is the ONLY system that would allow little people (as an entire country) to negotiate better health care prices. Little people don’t realize that the Medical Cartels already know that. And that is the reason why the Medical Cartels spend so much PAC money from the hospitals and doctors lobbying against a single payer system. Some little people say that a single payer system would cost you little people more. But if that were true, then wouldn’t the hospitals and doctors WANT that extra money? Yes they would. So why do the Medical Cartels lobby against a single payer system? It’s because the Medical Cartels know it would allow little people to negotiate better health care prices. And that’s what the Medical Cartels are afraid of. Period.
      But us big wigs at insurance companies, hospitals, and pharmacy companies don’t ever need to worry about health care no matter what it costs. We get our health care paid for one way or another by you little people. And we get the little people that work at our companies to contribute to our PACs. And us big wigs say it’s to protect the little peoples’ jobs. But in reality it would be in the little peoples’ best interest to NOT contribute to the PAC. Again, little people are so easily fooled. I won’t ever have to worry about losing my job with so many little people being brain washed by the Medical Cartels’ PAC money. Not only that, the Medical Cartels’ PAC money is used to elect so many republicans that will never allow a single payer system. Republicans have always fought against any meaningful health care reform. But that’s what our Medical Cartels’ PACs pay them for. Politicians can be bought so easily.
      Pretty soon the only people that will be able to afford health care is us big wigs. And that’s the way it should be. We don’t want you little people using up the resources when we need them. And once again, I thank you little people for capping my SS tax at the $117,000 level. Now I only pay 1.17% SS tax and you little people pay 6.2%. Also, thank you for extending my tax breaks. I’m using the extra money on my vacation houses.

      April 16, 2014 at 11:04 | Report abuse |
  10. CNN Propaganda Police

    I wonder who's paying CNN's bills this time. Last August, they posted this story from Dr. Gupta which was very pro-marijuana (http://www.cnn.com/2013/08/08/health/gupta-changed-mind-marijuana/). Today they post this unsourced garbage.

    April 16, 2014 at 10:11 | Report abuse | Reply
  11. boo radley

    Dr Gupta is known for his opposition to Marijuana and it shows in this article. If he wants to keep his credibility he should limit his comments to actual facts before drawing conclusions. Pot may well have some undesirable effects. Which should be studied and vetted before making blanket statements and conclusions. Of more concern to me would be studies and warnings about the thousands of industrial chemicals particularly the endocrine disruptors that are known to affect developing reproductive systems and significantly increase the risk of cancer.

    April 16, 2014 at 10:12 | Report abuse | Reply
    • jbcal2012

      Sanjay Gupta is not opposed to marijuana, he is for it. I don't know where you get your information. He didn't write this article.

      April 16, 2014 at 10:34 | Report abuse |
  12. claygooding

    The first thing I noticed,,besides the money that bought the research,is that they don't claim it is damaging the brain,,it is restructuring the brain,,is it for better or worse? Naturally NIDA and the DEA hope it is for the worse,,do we wait for another 50 years(that is how long NIDA has searched for actual harm from marijuana use)for government funded science to prove it "may" be harmful,,like it "may" restructure your brain?
    I wonder If all the college students for the last 50 years that used cannabis were harmed,,like Carl Sagan,Richard Branson,the last 4 Presidents and 80% of Congress?

    April 16, 2014 at 10:12 | Report abuse | Reply
    • Frank

      ...last 4 Presidents and 80% of Congress.

      That is all the evidence I need. All the lies, corruption, wasteful spending, lost lives of americans due to this group we definetely need to remove weed from our country!!!!!

      April 16, 2014 at 10:51 | Report abuse |
    • claygooding

      I did not mention them as a good reference but to the hypocrisy within our government,,every legislator that has smoked marijuana knows first hand knowledge that it is not the dangerous drug the DEA/NIDA claims it is yet they continue paying law enforcement grants for arresting and ruining young peoples live for the same thing they did in their youth.

      April 16, 2014 at 13:02 | Report abuse |
  13. PigBenis

    Sounds like a crock. They shouldn't publish these finding by doing one study on a few people. This article is a waste of inter-web space. I'm not a pot smoker but I am totally pro legalization. I know people that smoke who have great jobs and are very sharp.

    April 16, 2014 at 10:12 | Report abuse | Reply
  14. palintwit

    How about studying tea party patriots and the effects of guzzling Everclear from mason jars? Or the long term effects of being locked in a room full of squeaky balloons while listening to Sarah Palin's speeches?

    April 16, 2014 at 10:13 | Report abuse | Reply
    • Meyer C. Dhoates

      I would be rolling on the floor from laughing, but I don't want to get my clothes dirty. TOO FUNNY!!!

      April 16, 2014 at 10:49 | Report abuse |
  15. brad

    While the research is fine and information is generally a good thing (provided that it is accurate in its findings), I guess what I would like to see is who funded the research... Follow the money and we will see what agenda is in play

    April 16, 2014 at 10:14 | Report abuse | Reply
  16. thesaj

    Failed study. Study took those who smoke pot and compared to those who don't. Then noted that there were differences in the brains. Concluded, differences were due to pot.

    Second hypothesis, there are differences in the brains, and those who smoke pot, are doing so because it in fact compensates those differences (be it ADHD, depression, etc). That the pot may be no more than a treatment, no different than those patients prescribed Ritalin and Zoloft.

    April 16, 2014 at 10:19 | Report abuse | Reply
  17. Farrok

    Now if this article were true there would be millions and millions of dead and dying Americans as most of America has tried or used Pot occasionally.

    You would think Skid Row would be teeming and full of potheads? I have never seen a pothead living in Skid Row. Plus you ask any Neurologist and they will repot that this article is nothing but a complete lie.

    My question to all who read this where are the Dead from this Poison? You would think the morgues would be full after a Saturday night? Where are they?

    April 16, 2014 at 10:20 | Report abuse | Reply
    • helicohunter

      Just because marijuana doesn't kill you doesn't mean that it doesn't cause harm. People weren't dying due to lead poisoning back when lead was added to gasoline, but plenty of children had lower IQs and other damage because of it. I'm sure there were plenty of gas station attendants and oil company execs claiming that it was perfectly safe, but when enough research was done, the negative effects of leaded gasoline became very clear. There really haven't been many good studies done on marijuana use. Now that it has been legalized or decriminalized in many areas, more studies will be done. Other scientists will repeat this study using more patients or different patient populations. If they all get the same result as this study, then the conclusions of this study will be valid. If they get different results, then different conclusions will be drawn. Science isn't about any one study- it's about hundreds or thousands of studies.

      April 16, 2014 at 11:33 | Report abuse |
  18. tetch

    Clearly jail time is healthier than marijuana use

    April 16, 2014 at 10:22 | Report abuse | Reply
  19. oneSTARman

    Long term Pot use makes people less evil

    April 16, 2014 at 10:23 | Report abuse | Reply
  20. Charles

    Personally I didn't find the article convincing. It never really addressed the question of whether the alleged changes were harmful or not. I know way to many high achieving marijuana users in many different fields, including fields that require sharp minds. Frankly this reminds me of the phony ads I heard back in he sixties. The damage of this kind of agenda driven article is that kids hear this, try pot and don't see any downside and then assume that warnings about really dangerous drugs are bogus too. It just muddles the message. By the way, 1968 called and wants it's bell bottoms back.

    April 16, 2014 at 10:24 | Report abuse | Reply
  21. It'sTooLateNow

    Study-Author –> fails to report wether brain changes in study "that may have long
    term effects for later in life,"
    that were noted in the area of the brain thought to process emotion and task-reward realization,
    Were Positive Or Negative !!? (probably – they Dont Know That!!)
    EnJoY changing your brain while your still alive!!

    April 16, 2014 at 10:26 | Report abuse | Reply
  22. idlehands211

    They still called it an illegal drug...

    April 16, 2014 at 10:27 | Report abuse | Reply
    • Fred Evil

      Not in 40% of US state they don't.
      You must be referring to the defunct DEA and ONDCP who cling to Nixon's destructive and counterproductive mandate.

      April 16, 2014 at 10:28 | Report abuse |
  23. Fred Evil

    Crap headline CNN, and you know it. Just stirring the pot...so to speak.
    And I don;'t smoke joints, I vape, so am I safe now?

    April 16, 2014 at 10:27 | Report abuse | Reply
  24. Jay in Austin

    This "article" sounds like the writer was drunk and couldn't think of anything to write about. Probably just another case of somebody's brain getting changed and damaged by ... alcohol.

    April 16, 2014 at 10:30 | Report abuse | Reply
  25. Morpho

    The brain is plastic, affects and changes to it can be observed by a whole spectrum of what it experiences. This is how we learn, e.g. "synaptic pruning." You don't even have to ingest anything, a _picture_ of something you care about will register in fMRIs. Also placebos – pills that look like medicine but aren't – can have an effect on the brain and our perceptions. The claims made about how marijuana "changes" our brains implies that it's pathological, it makes us "sick." They said that about LSD in the 60s, that it "changes chromosomes" So does water. Let's not get too carried away about "sick in the head," okay Doc Gupta? Because rhetorical junk science like this has been misused as an excuse for genocide, among other things.

    April 16, 2014 at 10:31 | Report abuse | Reply
  26. compositor13@aol.com

    Thanks for the BS CNN. I've had my laugh for the day. When you talk out of both sides of your mouth, some of us notice. If you won't take a stand...how about you just take a seat!

    Big Hug.

    April 16, 2014 at 10:33 | Report abuse | Reply
  27. Farrok

    Here is a joker in the deck: Now if a person who is afflicted with Schizophrenia takes a MRI of their brain the images show their brain to be completely normal in all aspects! But that individual will be totally insane talking world salad, babbling and delusional?

    The essence is that this study is a complete fraud and reveals nothing at all. The general population of America has been using Marijuana for over 65 years+ if there were any serious problems they would have appeared by now.

    April 16, 2014 at 10:34 | Report abuse | Reply
  28. james

    Well that leaves me out, I don't smoke casually.

    April 16, 2014 at 10:34 | Report abuse | Reply
  29. citizenUSA

    This is why continual smoking is the recommended method.

    April 16, 2014 at 10:38 | Report abuse | Reply
  30. Phil Costastine

    Oh boy, the pro-MJ folks are all up in arms now CNN!

    For those spouting about the negative effects of alcohol and cigarettes, where in this article do they compare them to MJ? The doctors(ya know, the one's with medical degrees whom have spent years and years earning those degrees) in this study aren't articulating that MJ is going to kill you; they merely are observing and noting the changes in brain structure and development, particularly amongst younger users.

    April 16, 2014 at 10:38 | Report abuse | Reply
    • Bayside Lass

      Thank you Phil, couldn't have said it better myself.
      I get so tired of people comparing marijuana to alcohol. We are not discussing which is better or worse, this has nothing to do with any other drug, this is about marijuana.
      I also agree with Glen. I too smoked it in the 70s, and its not the same today. Carries lots more toxins thanks to cartels growing it. So not only do you have possible brain changes, but your lungs get a good dose of toxins from pesticides and herbicides.

      And I 'm so glad that most of you smokers don't have mental health issues. But for my son who started smoking with friends after school, he lost everything and is now conserved by the state, this article revels his reality. Brain changes, loss of IQ, lack of executive function, no goals, unable to concentrate or grasp new ideas. I have 4 kids Humboldt County grown, and only one with mental illness. Then one who smoked and continues to smoke. For him, it is dangerous. He becomes paranoid and psychotic. So although some people(brains) can handle it, there are others that suffer serious side effects. Its not user friendly to all. Which is all the study was pointing out. The is danger for young user.

      To Farrok,
      Have you looked at our news lately? The economy, job situation? Maybe you are correct that America has been smoking for 65 years now. ( But I say most of what you spouted is inaccurate and you need to read more). That could explain why the country is so messed up and about to collapse. You sound so much like my pot head son................have you had a brain scan lately?

      April 16, 2014 at 11:22 | Report abuse |
    • Fred Evil

      "We are not discussing which is better or worse, this has nothing to do with any other drug, this is about marijuana."
      Which necessitates a discussion of comparable substances. Alcohol is not directly comparable, as it is demonstrably MORE dangerous than cannabis, yet cannabis remains illegal.
      Is cannabis totally safe? Probably not, but water can kill you, aspirin is more lethal than cannabis. So is cannabis worth being prohibited? Almost certainly NOT.
      But it's good to have actual SCIENTIFIC studies being performed, instead of having to depend upon the DEA or ONDCP for their rhetoric explaining how EVIL cannabis is.

      April 16, 2014 at 17:16 | Report abuse |
    • Bobby C

      I have used cannabis on and off for about 40 years. In that time I have married, raised 3 children, owned and operated 3 business's and bought and sold 5 homes. I have done all the things non smokers do, paid my taxes, paid my bills and took care of my family. Is pot harmless? Most likely not. Is it a safer alternative to alcohol? Most definitely yes. If i smoke some pot on a Sunday nite, no matter how much or how little, come Monday morning I am up on time and ready to go. If I have more than two drinks on a Sunday night, come Monday morning I am lethargic, head hurts, possibly nauseous and am definitely not at my best. I don't go jumping in my car when I'm high. I don't go looking for confrontation when I'm high. I don't do stupid things when I'm high. I can't say the same thing when I have had a few drinks. I think , no matter what the articles focus is, that it is always fair to compare cannabis to alcohol. There is no question that it is safer and less toxic

      January 12, 2015 at 17:11 | Report abuse |
  31. Jodo

    This is not a study. It is an insult. You can drawn any conclusion that you like when your cohort consists of 20 people.

    This "study", and I use that term loosely, needs to be put in perspective. What does alcohol, tobacco, oxycodone etc. do to the brain? The most readily available drug on the planet, Tylenol, causes liver toxicity and death. Cannabis does not.

    April 16, 2014 at 10:42 | Report abuse | Reply
    • Two hi too Reed

      See above. I'm assuming you're a medical professional, specifically a physician of some sort, to come to your profound conclusion(s).

      April 16, 2014 at 11:06 | Report abuse |
  32. Porky O'Rourke

    If this study was accurate, I would be in a mental ward instead of being a successful computer programmer for 30 years.

    April 16, 2014 at 10:42 | Report abuse | Reply
  33. steve

    LOL, pure B.S., no horns, no tail, no Moooo in the middle, just pure crap.

    April 16, 2014 at 10:43 | Report abuse | Reply
  34. MICK

    In other news, alcohol and cigarettes are proven to actually KILL YOU but will still remain highly legal and available. Go figure.

    April 16, 2014 at 10:47 | Report abuse | Reply
  35. Sleeps


    April 16, 2014 at 10:47 | Report abuse | Reply
  36. Glenn

    The common response to these articles -- DENIAL .... DENIAL .. Without doing any scientific study - no fancy letters behind my name– just plain observation – FIRST- Todays pot Cannot be compared to the "quality or strength" of the dope I purchased 30 years ago...no comparison... Second - Based on my own teenage son and alot of his pot smoking friends - Lazy , Absolutely no ambition to do anything (maybe watch tv and play xbox) very slow to comprehend anything new or somewhat difficult , extremely forgetfull etc etc... Sorry – dont need a scientific report to be able to face the truth... way easier to deny it and just pass the pipe... Now – I have 2 daughters -one older and one younger than my son-neither has ever smoked dope... Both did/are doing excellent in school –straight A's – occasional B ... younger daughter works-has her own car she paid for (son does not –own an xbox tho) and older daughter owns her own home , car etc –put herself thru college -is currently a teacher at same school she graduated from etc etc etc... UUUMMM DAAA –get the point ....

    April 16, 2014 at 10:47 | Report abuse | Reply
  37. srcactus

    Mock the report to in the hope of acceptance of continued use?


    April 16, 2014 at 10:52 | Report abuse | Reply
  38. Responsible Pot Smoker

    I'm 49, and have been smoking pot for the last 20 years. I rank in the 98th percentile of Lumosity users in my age bracket (45-49). Now that's some analysis I'd be interested in seeing.

    April 16, 2014 at 10:54 | Report abuse | Reply
  39. Joe

    The only reason people don't think there is an effect is the brain cells die, what are they going to notice? They get dumber and dumber and so on. The rest of us notice and most are waaaaay too tolerant of the stupid.

    April 16, 2014 at 10:54 | Report abuse | Reply
    • Bobby C

      See now this is totally false! There is no proof that cannabis causes brain cell death. The same can not be said about alcohol though. It is a proven fact that alcohol causes BRAIN DAMAGE...not just changes in the brain but actual damage. I'm not saying that pot is harmless but it's not as though people just started using it last Tuesday. For the vast majority of users it causes very few (if any) problems either socially or medically. Yes, there are some who can not or should not use it because it causes problems for them for one reason or another. The same could be said for many legal drugs or for peanuts for that matter. Should peanuts be banned because they kill or injure some people?

      January 12, 2015 at 17:29 | Report abuse |
  40. Thomas

    For one how do we know these kids were telling the truth, they were being paid to be part of the study. For two how can it be proven pot was what was causing the changes in their brains, I'm sure the kids tested that said they casually smoked had already been smoking pot for a while. I'm sure that most of the kids saying they didn't smoke pot had used it before. How much alcohol had these kids been drinking, what kind of other drugs were these kids taking. There are a lot of other things more damaging that we could be spending time and money researching like the effects of trauma on the brain. The people with minds will see through it, while the ones who can't think for their selves will buy into it.

    April 16, 2014 at 10:54 | Report abuse | Reply
  41. helicohunter

    You don't get a study published in the Journal of Neuroscience unless the data are really good and proper controls were used. This is REAL science, not anecdotal evidence from cannabis users. In the past, it was hard to do good scientific studies because marijuana was so tightly controlled and people were afraid to even admit that they used it for fear of arrest. Now that the laws have been loosened, more studies will be done, and they will involve more people.

    April 16, 2014 at 10:56 | Report abuse | Reply
    • Responsible Pot Smoker

      I'm sure there's some scholarly research on the safety of Agent Orange, DDT, PCBs, PFCs, BPA, GMOs, etc., but I still don't drink bottled water, or eat GMO food.

      April 16, 2014 at 11:15 | Report abuse |
  42. TheSadTruth

    ANY substance that alters brain behavior is a type of poison. That includes alcohol and just about any narcotic. E was supposedly a "no cost" drug, until later it was discovered that taking it wrung out the dopamine from a user's brain, leaving them permanently depressed.

    To pretend that pot has NO effects is pathetic denial.

    April 16, 2014 at 10:57 | Report abuse | Reply
  43. Doctor R

    Ironically, legalizing pot might just be the best way to protect adolescents from using it. As any high school teacher can attest, it is easier for teens to get pot than alcohol. The reason is that because pot is illegal ,there are no controls on whom it can be sold to. People have the mistaken belief that society can make stricter and stricter prohibitions, the final one being illegality, in order to control drugs. The reality is that making something illegal means that the substance is completely out of control unless an arrest is made. To control pot, we need to legalize it to control who can sell it, what strength it can have, it's purity, it's price, where and when it can be sold, and to whom it can be sold. Ironically, legalization allows society more control, and therefore some hope of preventing some teens from getting it.

    The current illegality of pot means that no one can control it-except criminals. If we want to prevent teens from smoking pot, legalize it, and place it under social control. Any other policy opens the doors to gangs, drug dealers and criminals to provide drugs to children.

    April 16, 2014 at 10:58 | Report abuse | Reply
  44. Jon

    So... how do these changes in brain structure compare to those caused by, say, casual alcohol or nicotine use?

    April 16, 2014 at 10:59 | Report abuse | Reply
  45. Grumpster

    I would bet that religious indoctrination also causes brain changes...and changes that are far worse for society as a whole.

    April 16, 2014 at 10:59 | Report abuse | Reply
  46. Gregg

    I think its odd that your not going to or ever will get everyone to agree that casually smoking pot is not going to affect your health in some way.

    April 16, 2014 at 10:59 | Report abuse | Reply
    • zack

      everything affects your health in some way.

      April 16, 2014 at 11:04 | Report abuse |
  47. GOP Prayer - GOPers, Read Together and Out Loud With Me

    The GOP Prayer/Mantra/Solution: Dear God...With your loving kindness, help us to turn all the Old, Sick, Poor, Non-white, Non-christian, Female, and Gay people into slaves. Then, with your guidance and compassion, we will whip them until they are Young, Healthy, Rich, White, Christian, Male, and Straight. Or until they are dead. God...Grant us the knowledge to then turn them into Soylent Green to feed the military during the next "unfunded/off-the-books" war. God...Give us the strength during our speeches to repeatedly yell........TAX CUTS FOR THE RICH!!!..........and........GET RID OF SS AND MEDICARE!!!
    In your name we prey (purposely misspelled, or is it?)........Amen

    April 16, 2014 at 11:00 | Report abuse | Reply
  48. oh please

    SOMEONE needs to point out that the average pot smoker doesnt smoke JOINTS- they take hits- they smoke bowls. They dont smoke an ENTIRE JOINT except MAYBE once a month if that- smoking a joint, is getting STONED- ok? Very few experienced pot smokers get THAT wasted- your average pot smoker will smoke a bowl every 3 to 4 hours- an entire joint is excessive- you might as well drink an entire bottle of whiskey- very few people who are experienced smoke an entire joint- those who do end up doing things like cutting off fingers when making sandwiches or forgetting their children

    April 16, 2014 at 11:01 | Report abuse | Reply
  49. R.A. Chapman

    Breaking news, so does alcohol, air pollution, bad news reports, etc......

    April 16, 2014 at 11:01 | Report abuse | Reply
  50. Doctor R

    I just noticed that the program replaces " its" with "it's" in entirely inappropriate ways. Read my previous post to see a program with make grammatical mistakes on purpose. "It's" means " it is". The possessive form is "it's".

    April 16, 2014 at 11:02 | Report abuse | Reply
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Get a behind-the-scenes look at the latest stories from CNN Chief Medical Correspondent, Dr. Sanjay Gupta, Senior Medical Correspondent Elizabeth Cohen and the CNN Medical Unit producers. They'll share news and views on health and medical trends - info that will help you take better care of yourself and the people you love.