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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 (757 Responses)
  1. Smartest Man

    It should be decriminalized, but you should be fined if it is in your possession and you are under the age of 25.

    April 16, 2014 at 11:54 | Report abuse | Reply
    • Thomas

      Why 25? You can go to war and buy cigs at 18, you can buy alcohol at 21. So why 25 for pot?

      April 16, 2014 at 11:59 | Report abuse |
    • Julie Rambow

      This is for Thomas....25 is when your brain is finished developing in the frontal lobe and this area is responsible for understanding consequences.

      April 16, 2014 at 12:18 | Report abuse |
    • Thomas

      So it's alright to put 18 yr olds in traumatic situations like war, or let them smoke cigs, and it's alright to let 21 yr olds drink alcohol all before their brains are fully equipped to understand consequences, but pot is different so not until they are 25. Sounds logical to me.

      April 16, 2014 at 12:22 | Report abuse |
    • shane

      I would suspect alcohol is just as bad if not worse in permanent adverse effects to the brain....Maybe we should re-evaluate the drinking age then? Or we could just let young adults make their own decisions. We certainly have no problem thrusting them into the battlefield at age 18 before the brain is fully developed.

      April 16, 2014 at 12:23 | Report abuse |
    • Sean

      So am I understanding this correctly? You started the study to test the colloquial hypothesis that pot is 'bad?' shouldn't you maybe try coming at it from a more neutral standpoint? I mean, I understand that to run a test on something you have to have a hypothesis to begin with, but this wasn't a hypothesis. Its just something people say. Also, doctors have been saying for YEARS that MJ stunts brain development in young people, this is not new information. Can you run the study with people in their 40's? I'd like to see that data.

      April 16, 2014 at 12:27 | Report abuse |
    • blueangel2992

      This is to thomas not you Smartest man,
      Did you read the article?
      It clearly stated that marijuana use is detrimental to the maturing brain which is from birth to about 25 years of age.

      April 16, 2014 at 12:32 | Report abuse |
    • Thomas

      Blueangel, where does the article say it is detrimental? Did you read it? It says pot changes the brain and they don't know if harmful or not.

      April 16, 2014 at 12:44 | Report abuse |
    • goldenwhitespirit

      My question is this – why didn't they do this study on adults who smoked from the time they were teens and see how their brains and lives are compared to those who didn't? I smoked almost daily for over 20 years beginning when I was about 16. I quite cold turkey at the age of 39. I just didn't care to smoke anymore – my life changed after ending an abusive relationship. However, some things in the above article ring true in my case. Although I've never had my brain scanned for this reason (I had an MRI this last year and everything looked normal for what they were looking for), I am not an emotional person nor am I motivated by monetary rewards. I consider myself a "free thinker" and am not easily influenced by media, commercials or propaganda. My joys in life come from being able to provide for my family and seeing those I love – my kids, friends and family do well in their lives. Is that a bad thing? I am not money motivated at all so I guess that's why I'm not easily influenced or controlled. Maybe that's why marijuana is a bad thing to those who "run" society.

      April 16, 2014 at 12:54 | Report abuse |
  2. Buddha

    People have died from comsuming too much water. We should outlaw it.

    April 16, 2014 at 11:57 | Report abuse | Reply
    • sumguy2006

      You need water to live Einstein.

      April 16, 2014 at 11:59 | Report abuse |
    • MM

      "You need water to live Einstein."

      Wow, nothing gets past you, Captain Obvious.

      April 16, 2014 at 12:02 | Report abuse |
    • tjp44

      you need water for your bong or bubbler.....!

      April 16, 2014 at 12:42 | Report abuse |
  3. mikes

    "You are old, father William," the young man said,
    "And your hair has become very white;
    And yet you incessantly stand on your head —
    Do you think, at your age, it is right?"

    "In my youth," father William replied to his son,
    "I feared it would injure the brain;
    But now that I'm perfectly sure I have none,
    Why, I do it again and again."

    April 16, 2014 at 11:57 | Report abuse | Reply
  4. DC

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

    She should look at all of the alcohol studies for substance addiction, then. I'm pretty sure this base has been covered.

    April 16, 2014 at 11:58 | Report abuse | Reply
  5. Spendlove

    Strange, CNN is now reporting on articles that Fox News is making a big deal of. Though guess I'm not surprised considering CNN has been full of mostly opinion pieces of late.

    April 16, 2014 at 11:59 | Report abuse | Reply
    • sumguy2006

      A study published in the Journal of Neuroscience is not an "opinion piece"

      April 16, 2014 at 12:02 | Report abuse |
    • Erik

      It's very typical of Fox.. I'm sure they'll distort & sensationalize the truth with this issue too. These writers and producers are the same ones chain smoking their cigarettes before spraying that air freshener to hide the fact, and drinking their bottle of whiskey per night habit then hiding it in cheap cologne. ...Remember these are/were the"Pot's an abomination sent from the devil" folks. (ughs & groans)

      April 16, 2014 at 12:38 | Report abuse |
  6. the_dude

    Well I am safe because I only smoke bong rips not joints. Whew!

    April 16, 2014 at 12:00 | Report abuse | Reply
  7. sumguy2006

    This is not a news flash for anyone who had a few "stoners" in their high school.

    April 16, 2014 at 12:00 | Report abuse | Reply
    • stoney

      I was a toner on sigh hchool and my drain was not bamaged

      April 16, 2014 at 12:19 | Report abuse |
    • lucas

      I was one of those "stoners" in high school and graduated in the top 10 of my class with a 3.5 GPA. It's all individual; no drug affects everyone in the same fashion.

      April 16, 2014 at 12:24 | Report abuse |
    • swyrlpr

      I had a 2.5 GPA in HS before I started using MJ.

      I had a 3.2 GPA in college after I started using MJ.

      It's clear that I became less intelligent as a result of MJ.

      April 16, 2014 at 12:57 | Report abuse |
  8. Cruz

    8th a day keeps the doctor away.....

    April 16, 2014 at 12:02 | Report abuse | Reply
    • Mary Jane

      Awesome. Agreed.

      April 16, 2014 at 12:15 | Report abuse |
  9. HURC

    Big pharna is going to be pumping out bs studies like this for a long time to come (40 people really....absolutely no scientific relevance at all).

    April 16, 2014 at 12:03 | Report abuse | Reply
    • NOReally

      Yeah...keep telling yourself that. It couldnt possibly be true.

      April 16, 2014 at 12:18 | Report abuse |
    • tjp44

      it's rarely true.......

      April 16, 2014 at 12:43 | Report abuse |
    • to HURC:

      Why don't you pull the paper and read who funded the study? Pharmaceutical companies don't fund science like this. These researchers used MRI scans to measure volume and blood flow. Scanning 40 patients (20 per group) is a pretty big study and if the statistics indicate significance taking into account the mean values, standard deviations and sample size, it's good. Get a clue before you spew out your standard unfounded rhetoric: "the evil pharmaceutical companies". Just so you know, companies already market pure THC and other cannabinoids for research use. That HELPs your stoner cause, not hurts it. Comments like yours actually support the results of this study if you are/were a stoner.

      – a scientist

      April 16, 2014 at 12:47 | Report abuse |
  10. craigbhill

    Marijuana, which i first tried when i was 18 and did not use all that much until i was 23, has always made the neurons of my brain pulse faster, thoughts becoming clearer, not cloudier, as the THC slows down observations allowing me to explore them in much greater depth than in the everyday, superficial, shallow world. For me, it is a great tool for understanding the world much better than without it. The effect is not cartoonish as always depicted, allowing me long hours of fully awake conversation, not the "Hey, man" babble as if lobotomized it is criticized for inducing.

    April 16, 2014 at 12:05 | Report abuse | Reply
    • Jake Billington

      The stuff makes you a witless dullard. Try and get some feedback from sober acquaintances (if you have any) about how you act and behave when you're on the stuff.

      April 16, 2014 at 12:23 | Report abuse |
    • lucas

      Same, I agree 100%

      April 16, 2014 at 12:25 | Report abuse |
    • shane

      It adds to your quality of life, I am happy for you craigbhill. Don't listen to sheeple like Jake who are just angry at the world. Heck, he is probably a paid troll for the anti-cannabis/pharma industry.

      April 16, 2014 at 12:37 | Report abuse |
    • Jake Billington

      The world is too beautiful to be mad at, and life is too full of opportunities to be bitter. If you can't see that while sober, you're doing it wrong.

      April 16, 2014 at 12:45 | Report abuse |
    • tjp44

      yes, it's not like we all hang with Jake......most of the time, no one even knows wheter you did or did not......so jake, climb off Mount Pretentious

      April 16, 2014 at 12:46 | Report abuse |
    • Jake Billington

      That's right, hide the shame and fear of what you've done to yourselves behind defensiveness. No matter how much you wish it to be so, cannabis is not good for you. No matter what drug induced lies and delusions you tell yourselves and revel in, you cannot reach your full potential by wasting away your brain cells. You cannot make believe the consequences away.

      April 16, 2014 at 12:53 | Report abuse |
    • for craigbhill

      Try mindfulness in which you purposefully think only what what is around you right now. Filter out the gibberish and thoughts of the past and future. This is another way you can think clearly and it's free and legal.

      I think Jake does have an excellent point about asking your sober associates about your behavior when high. I've observed many people when high and they do behave differently. Some are already stupid people who become even stupider and some become activated. I don't think this phenomenon is as obvious as comparing a drunk person ("I'm fine to drive home") with the sober observer who sees weaving, hears slurring and doesn't want to get in the car with that person driving. If people want to use at home without driving anywhere and no kids around, that's probably ok. Showing up for work high is not ok.

      April 16, 2014 at 12:54 | Report abuse |
  11. larry

    40 people tested, 40! Global Warming type numbers.

    Doesn't it seem that if the results were true or even close that hospitals around the world would be seeing these "abnormalities" in ever increasing numbers?

    40 people tested.....

    April 16, 2014 at 12:06 | Report abuse | Reply
    • Mary Jane

      Very good point. A very small sample in our population... Note it did say had no effect on their studies or social lives. This is a boasted reporting piece.

      April 16, 2014 at 12:17 | Report abuse |
    • .

      Larry, there types of scans cost about $2,500 per volunteer. Let me do the math for you. That's $100,000 just for scan time in the magnet alone to do this study. 40 volunteers is a good number and they would only indicate significance (a statistical term) if the p value for a giver brain region was < 0.05.

      These types of scans are not done on typical patients because it a special morphometric scan that takes longer to aquire and process than a typical anatomic scan looking for tumors, stroke, inflammation. The blood flow scans are also mostly done only in research setting because it requires a 3T magnet to get adequate resolution and the expertise to process the data.

      Don't rip what you don't understand.

      April 16, 2014 at 13:00 | Report abuse |
    • Bobby C

      Really? Is that what it "costs" or is that what they charge you for it. My guess is it costs waaaay less then 2500 bucks.

      January 12, 2015 at 18:05 | Report abuse |
  12. phoenixhawaiian

    We already know that ciggarette's kill you, its not even a maybe . so whats the point of this article about MAYBE's?

    April 16, 2014 at 12:07 | Report abuse | Reply
  13. Jason

    This study really says nothing other than more studies are needed which I am all for but for me personally, Mary isn't doing any more damage to my brain that old age isn't taking care of first. Education is the answer not prohibition.

    April 16, 2014 at 12:07 | Report abuse | Reply
  14. Topdogman

    I call total BS on this, very small study group. Also, in my opinion, shouldn't smoke weed until a persons brain has matured – if that makes sense. Worked many jobs w/ 25 and older, dumb as posts sometimes, I'll ask did you smoke weed when you were 12? 13? More often than not they'd say yes. Just saying.

    April 16, 2014 at 12:10 | Report abuse | Reply
  15. glades2

    I've suspected that for years – those I've known since from the late 1960s through 1990s who used marijuana more than once seem to have been left with a diminished cognitive function level, as if they have breaks in their mental state from time to time, similar to those I've known who used LSD and who told me that they were left with mental breaks that will also happen from time to time. The husband of one couple I've known for years once told me of his LSD use during college and to this day (he's in his 60s now) I'll see them and sure enough some times he's of a normal state and others he'll seem to disconnect for a moment and return to normal, almost as if he's having a seizure of some sort, but as he and his wife told me that started after his LSD use decades ago, and again is similar to those I've known who used marijuana, and is why the current CO and WA laws are a disaster in the making – if we worry about an increase in autism diagnosis over the past decade, just wait until regular marijuana users begin to be diagnosed with cognitive disorders – there won't be enough neurologists to handle the caseload..

    April 16, 2014 at 12:11 | Report abuse | Reply
    • Julie Rambow

      The effects are supposed to be minimal to the brain, see other studies on this and make sure they are of course from/screened by a University. It will have some effect but it is easier on the body than other pain blockers which rip up the liver....it has temporary sterilizing effects I believe too. It is still the best choice for migraines....and 1/4 of the price for the meds. I don't think it should be used other than for medicinal though. But I'd worry more about alcoholism before pot, and eating French fries which can actually kill you. (Assuming people don't use pot while driving).

      April 16, 2014 at 12:28 | Report abuse |
    • Bobby C

      So, now, because it's legal, this is what will happen? Why has it not happened already then? Oh, except for your imaginary friend that is.

      January 12, 2015 at 18:08 | Report abuse |
  16. someone

    Very sketchy to say "structural changes" are "bad". Maybe it's not a bad change at all. If they actually understood the brain structures themselves it would be a different story. But they don't. So they say something that sounds scary and people who don't analyze it believe their ridiculous conclusions.

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

      I did notice that the reported only that there were changes, making no comment on the nature of those changes, nor noting what the effects of such changes tended to be. Between that and the small sample size, it's all a bit alarmist.

      April 16, 2014 at 12:42 | Report abuse |
  17. walter

    Oh suck it CNN.
    And when did you hire a fox reporter?

    April 16, 2014 at 12:13 | Report abuse | Reply
    • Mary Jane

      *applause *

      April 16, 2014 at 12:19 | Report abuse |
    • tjp44

      nothing more than a tabloid now....top stories revolve around Cyrus, Kardashian and atheletes coming out as gay........pathetic journalism!

      April 16, 2014 at 12:52 | Report abuse |
  18. William

    What is this article about i forgot. 🙂

    April 16, 2014 at 12:14 | Report abuse | Reply
  19. polly

    OF COURSE it effects the brain. That's WHY people use it.

    April 16, 2014 at 12:14 | Report abuse | Reply
    • tjp44

      classicly beautiful!!!!

      April 16, 2014 at 12:55 | Report abuse |
  20. Sebastian

    This research seems to be limited to 'joint' smockers... those who smocke pot out of a rolling paper that has the same toxicity and carcinogens than tobbacco... what about pipe, bong or vaporizer users.... or Marinol users ???

    April 16, 2014 at 12:14 | Report abuse | Reply
  21. Mary Jane

    These are great responses. Especially the ones that highlight ALCOHOL IS WAY more harmful than marijuana will be any day. we don't allow 16 year olds to drink so we shouldn't allow them to smoke legally. That's why there's an age limit. How I'd alcohol any different? Its way worse and causes way more deaths.

    This is an opinion piece because the style and language is clearly biased. And I'm sure this leaves out a lot of other relevant information that is in the study. People who are ignorant on their views and "facts" on marijuana are misinformed and uneducated on the matter.

    April 16, 2014 at 12:14 | Report abuse | Reply
    • meledir

      The study found that alcohol use was more common among the marijuana users than among the control group, which is not a good start if we're legitimately concerned about alcohol.

      April 16, 2014 at 12:19 | Report abuse |
  22. Yakker

    How Does Marijuana Affect a User’s Life?

    Research shows marijuana may cause problems in daily life or make a person's existing problems worse. Heavy marijuana users generally report lower life satisfaction, poorer mental and physical health, more relationship problems, and less academic and career success compared to non-marijuana-using peers. For example, marijuana use is associated with a higher likelihood of dropping out of school. Several studies also associate workers' marijuana smoking with increased absences, tardiness, accidents, workers' compensation claims, and job turnover.

    http://www.drugabuse.gov/publications/drugfacts/marijuana

    April 16, 2014 at 12:15 | Report abuse | Reply
    • Taalex

      Hmm, it looks like you just copied/pasted the effects of alcohol from Wikipedia, which is perfectly legal BTW.

      April 16, 2014 at 12:34 | Report abuse |
    • tjp44

      yes, MJ use aused me to get my Master's one quarter later....awful!!!!

      April 16, 2014 at 12:38 | Report abuse |
    • swyrlpr

      Those are all interesting correlations affecting users of canabis but those correlations are not proof of causation. The fact is that there are a lot of dumb, lazy people that use drugs and some of those people choose canabis. So did they become dumb and lazy because of marijuana or were they just dumb and lazy before they started using marijuana?

      I would say that generally speaking intelligent and motivated individuals are less likely to use canabis, therefore it stands to reason that non-users would have fewer issues such as those you list.

      April 16, 2014 at 12:44 | Report abuse |
  23. Beth

    So does anti depressants and chemotherapy... among other legal drugs. Im on chemo now. It's worse on my brain than anything I have EVER had..

    April 16, 2014 at 12:16 | Report abuse | Reply
  24. Nicholas Chambers

    Has this study been done on other tobacco products? My hypothesis would be there would be similar results.

    April 16, 2014 at 12:17 | Report abuse | Reply
  25. Dumber than most

    It is amazing how the new scholars have all this research data from recent studies! 90 days of research. WOW Amazing!
    Come and talk to some of us that have used this medicinal cure for 40+ years, DAILY not once a week. They are still awarding patents to me as of last week, I must be really stupid from using this from the time I was 13 years old. My long term implications – I provide solutions to solve real problems daily, where they call me "An Inventor" and award patents.
    Maybe I should go "Practice" more as the doctors do and see what happens in another 30 years.

    Wake up you ignorant idiots!

    April 16, 2014 at 12:17 | Report abuse | Reply
  26. William

    Dr. Sanjay Gupta must be stoned because he can't make up his mind whether marijuana is good for you or marijuana is not good for you.

    April 16, 2014 at 12:21 | Report abuse | Reply
  27. flyin high

    Been smoking for 25+ years on a daily basis. I am not brain damaged. i hold down a full time job, have my own house and 2 cars. basically living the american dream. Cigarettes and alcohol are far more dangerous than pot.

    April 16, 2014 at 12:22 | Report abuse | Reply
  28. Mary Jane

    You are awesome. Keep doing what you're doing. You know how to live your life and youre doing just fine. I hate when government tells us what to do and how to live our lives.

    If you drank daily for 40 years I highly think your cognition and activity would be way different and worse than it is now with your current activity

    April 16, 2014 at 12:23 | Report abuse | Reply
  29. NOReally

    It is amazing how people, when presented with anything contrary to what they want to believe will lash out....statements such as alcohol and tobacco are worse than weed. Really? Who cares what is worse. The fact is, weed is harmful (and so are tobacco and alcohol). The article isnt debating the legallity of anything. It is simply pointing out what non-stoners have known for years....that there must be something wrong with your brain!

    April 16, 2014 at 12:23 | Report abuse | Reply
    • Taalex

      Personally, I lash out because I don't like being hoodwinked. The legality is the ONLY issue, not the effect on one's brain. If legislators and lobbyists were at all concerned with harmful effects on our health, then alcohol, tobacco and about million prescription drugs would also be illegal. Yet, they are not and marijuana is. We don't deny that there is an effect. We just want an explanation to that conundrum.

      April 16, 2014 at 12:42 | Report abuse |
  30. HorseDoctorDVM1

    "Casual marijuana use may damage your brain"?... As my daughter used to say, "Well, DUH!!!" All you had to do is look at how Miley Cyrus turned out to come to that conclusion...

    April 16, 2014 at 12:23 | Report abuse | Reply
    • swyrlpr

      The problem with your statement is that the article doesn't say anywhere that it does "damage". It says the study shows that there are chemical changes in the brain from the use of canabis.

      The real shock is that CNN wasted our time with an article that is the equivelent of reporting that water is wet. Everything we put into our body creates changes in us.

      April 16, 2014 at 13:06 | Report abuse |
  31. matey

    To all you people from Colorado and other pot users: This article say weed does affect your brain. Your trial year is not over yet. Enjoy your highs now because your days of legal POT will be ending after this trial period. When you toke up, remember your brain is being affected and you will get dumber than your present condition. When you get arrested, after Weed becomes illegal again. you can recover and correct your problem while sleeping in a Jail Cell. You have just been warned. So take care of yourself all of you who believe that Marijuana is harmless, you bunch of bongheads.
    However, There still is some benefits for those who have justified medical problems. However, I hope the cure is not worse than your medical problems.

    April 16, 2014 at 12:25 | Report abuse | Reply
    • Epoxide

      One thing is for sure – you're a total moron, stoner or not.

      April 16, 2014 at 12:59 | Report abuse |
    • Bobby C

      And then you woke up!

      January 12, 2015 at 18:15 | Report abuse |
  32. Kal-El

    As Chevy Chase use to say "it causes Dain Bramage"

    April 16, 2014 at 12:26 | Report abuse | Reply
  33. me*

    Really, a study of 20 users/non-users?!

    It doesn't say whether they did preliminary MRI's to see percent change. What if the people had the enlarged areas to begin with?

    April 16, 2014 at 12:26 | Report abuse | Reply
  34. Ollie Tinsley

    Alcohol damages your brain.....

    April 16, 2014 at 12:27 | Report abuse | Reply
  35. Bob

    4/15/14
    Did anyone else watch an interview today of Willie Nelson ? A lot of the interview was specific about his use of marijuana,and he was very open and honest about that use. When asked about how often and how long, his answers were since he was a very young boy,and he cant remember missing a day since then. He feels the use has helped him with his occupation which he considers is songwriting. He is in his 80s and does a show nightly.He quit smoking tobacco because he felt it was harming his health, but said he felt the opposite was true of marijuana, A really good interview by Larry King.

    April 16, 2014 at 12:28 | Report abuse | Reply
  36. Sean

    Also, why should we trust any study on ANY drug done in the United States? We've been lied to for years. i.e. the "gateway" theory, "Reefer Madness" and Nixon disregarding his own commission on the effects of MJ.

    Do the study in Israel. They don't have outrageous restrictions on testing MJ. The only people in the US who can test MJ have to be approved by the government. The government says MJ is bad. So why would they allow anyone who doesn't think its bad to study it? see the Nixon commission again.

    April 16, 2014 at 12:31 | Report abuse | Reply
  37. lool

    This study is such BS. First off. They made these people smoke it. They also said joints. Joints are filtered like water or a vaporizer. Any smoke in the lungs will increase risk of all sorts of things.

    April 16, 2014 at 12:31 | Report abuse | Reply
  38. John Illinois

    Get real people! When you were in high school and saw the people that constantly smoked pot you knew they were worse academically and generally lazy/no motivation....all they worried about was their weed. You do not need a study for this.....you already saw it!

    April 16, 2014 at 12:33 | Report abuse | Reply
    • tjp44

      nice stereotype John! Doctors and Lawyers today are just woried about their pot! get real

      April 16, 2014 at 12:35 | Report abuse |
  39. CaptOutrageous

    It's in the "Zig Zag Rolling Papers"! Same with Tobacco! It's all in the chemicals they use to manufacture the papers. Smoke a pipe or a bong and the results might be different. Smoke cardboard daily and see what happens to the brain......

    April 16, 2014 at 12:33 | Report abuse | Reply
  40. tjp44

    more and more using every day....scare tactics went out in the 60's.....!

    April 16, 2014 at 12:33 | Report abuse | Reply
  41. Esaias

    "Casual marijuana use may damage your brain."

    Duh.

    April 16, 2014 at 12:33 | Report abuse | Reply
  42. Janae

    I am sure, as with any "drug", there are side effects for some people. That in mind, I believe it does more good than harm. There is always going to be someone who disagrees with it and will pick it apart, grasp at straws to make it an issue and regulate the crap out of it because it "may"or "might" do something. I take articles like this with a grain of salt.

    April 16, 2014 at 12:33 | Report abuse | Reply
  43. Inciteful

    CNN has given a lot of exposure to Sanjay Gupta's current position on cannabis use. Now, without qualification or editorial, CNN publishes this story. In my opinion, CNN has an obligation to reconcile these two, seemingly opposing, views. At the very least, CNN should have Dr. Gupta author an article that addresses the findings reported in this article. He doesn't need to defend his recently publicized position, but he should let CNN readers know if this article represents new information that might give him pause.

    April 16, 2014 at 12:35 | Report abuse | Reply
    • Inciteful

      It would be informative if those who have conducted these studies would follow the same protocols with alcohol. Naively, I would suspect that the adverse effects on the brain of recreational drinking would be as dramatic, if not worse, than cannabis.

      April 16, 2014 at 12:40 | Report abuse |
  44. battlin

    Maybe some of us need our neuro receptors rewired!
    I wonder what Carl Sagan or Bill Gates or Steve Jobs would have produced had they not smoked pot. There are plenty of doctors and engineers and scientists that have been smoking for 40 50 60 years. I suggest we study their brains and see what we can gleen from the impact it has had on their concentration and focus. There has been a case study going on for half a century now with a sample substantially larger than 40. I think the evidence is obvious. Don' smoke at 16 and don't smoke 10 joints a day. How about focusing on the medicinal qualities and study that. Lets not let an agenda get in the way of our science or we will be burning modern day Galilleo's at the stake.

    April 16, 2014 at 12:35 | Report abuse | Reply
  45. Thomas

    This is to blueangel, the article says it changes the brain, and they don't know if the changes were harmful, none of the users reported any ill effects in school, family or any other areas. The article does not say it is detrimental.

    April 16, 2014 at 12:36 | Report abuse | Reply
  46. swyrlpr

    Woh, hold the horses and put down the torches and pitchforks. This article is not the original research paper and this article takes some liberties and make implications that go beyond what the study discovered.

    The fact is that any chemical we put in our body is going to "create changes" so an article that states as much is really not telling us anything that we don't already intuitively know. In fact, careful reading makes it clear that the scientists that performed this study do not know if the changes in the brain are an improvement or a detriment to our brains functions.

    This article is premature and a smidge hyperbolic. It's possible that these changes are not detrimental or not so detrimental that they are cause for alarm. There are chemicals we put in our food that we know cause damage to our bodies but that hasn't stopped food manufacturing companies from putting it into their products (Nitrites for example).

    I am well educated and a regular pot smoker myself. I might be so bold as to say that it's possible the changes are for the better as some studies suggest. However, I admit that until more comprehensive research is done, I can only suggest it.

    April 16, 2014 at 12:38 | Report abuse | Reply
  47. Matt

    Excess consumption of alcohol is the 3rd leading lifestyle-related cause of death for the nation, according to the CDC, killing 88,000 people/year. You can begin to drink legally at age 21, be sent to war and killed or maimed at 18, but don't smoke any marijuana!!! It won't kill you, but it "might" effect" the way you think. Yes... makes complete sense.

    April 16, 2014 at 12:39 | Report abuse | Reply
  48. Lonesome Louie

    Explains why liberals think the way they do.

    April 16, 2014 at 12:39 | Report abuse | Reply
    • swyrlpr

      Your declaration demonstrates that lack of critical thinking of conservatives.

      April 16, 2014 at 12:55 | Report abuse |
    • Jake Billington

      It has always struck me as ironic that the same people who tout their academic and intellectual prowess are the same people who ardently defend the use (especially their own use) of marijuana. It's almost like living through the story "The Emperor's New Clothes"

      The question is how long before people start waking up.

      April 16, 2014 at 13:06 | Report abuse |
    • Janae

      Both of your statements suggest to me a separation in humanity, lack of empathy and an allergic reaction to an open mind that having a "party" seems to bring.

      April 16, 2014 at 13:06 | Report abuse |
    • swyrlpr

      Jake Billington, it strikes me that those most critical of marijuana use are often scientifically illiterate and often overstate the conclusions of a study that they believe supports their standpoint.

      Read the article again but pay attention to the last paragraph.

      April 16, 2014 at 13:28 | Report abuse |
  49. Jake Billington

    Now a question... How many of you ardent defenders of Marijuana's virtues go out and fight just as hard against vaccines because of the supposed health risks they pose?

    April 16, 2014 at 12:40 | Report abuse | Reply
    • Janae

      I don't think it matters what issues or how many different issues you feel strongly about, as long as you feel something and stand for what you believe in. The world is in constant conflict on so many issues. Everyone worrying about something. We can't all be on the same page about everything. Tolerance 🙂

      April 16, 2014 at 12:50 | Report abuse |
    • Matt

      Vaccines SAVE lives... sorry, but the myths about vaccines have been debunked.

      April 16, 2014 at 13:55 | Report abuse |
  50. Nathan

    Why is this news? I thought the whole reason people smoked marijuana was to change their brain state. Until we learn more about whether and how mj changes functioning and capability–and until we get better reporting that gives a more complete account of the experimental procedures–we will still be in the dark. I'm pretty sure that many people who support decriminalization and legalization do so on other grounds than the case that mj does nothing to change the brain. I myself am convinced enough by existing science to believe that regular use is a bad idea for me–I want optimal functioning and health. The question is how severe and what kind of negative affects it has, in this case, on under-25s. It's a good question, but we need so much more than what we get here.

    April 16, 2014 at 12:41 | 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.