Early Marijuana Use Linked to Brain Problems Later in Life

Early use of marijuana maybe more harmful than previously realized.  According to new research, early users of marijuana may face cognitive difficulties compared to those who start using marijuana later in life or not at all.

With the increasingly complex world in which we live, most of us strive to live up to our full cognitive potential… those who’re exposed to marijuana at an early age may actually be causing themselves problems later in life–this despite the widely popular misperception that weed is organic / completely safe.

Specifically, young adults who being smoking marijuana prior to the age of 16 performed worse on cognitive testing when compared to those who’ve never smoked marijuana before or those who starting smoking after the age of 16 says researcher Staci Ann Gruber, PhD, of Harvard Medical School and McLean Hospital, Boston.

Findings from Dr. Gruber’s research was presented on Monday at the annual meeting of the Society for Neuroscience in San Diego.  For years, researchers in the field of psychiatry have speculated a connection between EARLY exposure to marijuana and psychotic disorders.

Does Weed Use Contribute to Cognitive Problems?

Though previous studies have found that early marijuana use can lead to cognitive problems, this is the first study to compare early users to late users.  Gruber also noted:

“Early-onset smokers smoked twice as often and nearly three times as much.”

For her research, Gruber compared 35 chronic marijuana users and compared them to 28 healthy volunteers.  2o of the chronic marijuana users started smoking prior to age 16 while the remaining 15 started afterwards.

The cognitive testing was evaluated using the Wisconsin Card Sorting Task which is a measure of one’s executive function.  Executive function includes involves tasks such as abstract thinking, planning, and decision-making.

The healthy volunteer group outperformed both groups of chronic marijuana users on several measures.  Early-onset smokers did worse than late-onset marijuana smokers in terms of making significantly more errors.

Francis Jensen, MD, speculates that marijuana exposure ‘is somehow modifying the way that part of the brain [the prefrontal cortex, involved in executive function tasks] is developing.”  The prefrontal cortex is one of the last areas of the brain to fully develop which may make teens particularly susceptible.

Early Marijuana Use and Educational Achievement?

In other related news, New Zealand researchers recently published a meta-analysis based on 3 Australian cohort studies involving 6000 participants which looked at educational outcomes following different ages of marijuana use [2].

The New Zealand researchers found that there is a robust association between age of onset of cannabis use and subsequent educational achievement.  Educational attainment was highest for those who had not used cannabis by age 18 and lowest for those who did use cannabis prior to age 15.  Oddly, the researchers noted that the data suggests that there’s a greater detrimental effect of cannabis use on university enrollment in males than females.

From the Study Authors:

“Pooled estimates suggested that early use of cannabis may contribute up to 17% of the rate of failure to obtain the educational milestones of high school completion, university enrolment and degree attainment.”


  1. WebMD
  2. Drug Alcohol Depend. 2010 Aug 1;110(3):247-53. Epub 2010 Apr 24.

22 thoughts on “Early Marijuana Use Linked to Brain Problems Later in Life

  • March 24, 2012 at 1:03 pm

    Nice article Jarrett.  “Probably” not a good idea for children under 16 to use marijuana?! What?!? In no uncertain terms should a CHILD or developing teenager use drugs/tobacco/alcohol.  Legal or not in a perfect world it’s medical/recreational use should be reserved for legal adults.  I know I know that’s not reality.  Bottom line the vast majority of all hard drug users & addicts begin with weed.  They get it from a dealer usually.  Who knows what’s in it, where it’s from, etc. In recent months a local teen was murdered by a stoned friend who he’d been smoking “pot” with. Well well well, wouldn’t ya know it was laced with something.  Grieving family, life lost, devastated teen on trial all for a “harmless” high.  In response to those comments about happy meals being worse for you than marijuana.  I agree, however we aren’t comparing apples to apples here.
    Most don’t smoke joints they rolled from the plant the grew in their organic garden.  Gotta go with Nancy Reagan here, JUST SAY NO.  Unless you are an adult with medicinal needs who can get it legally and safely, then go for it.  

  • November 23, 2010 at 12:33 pm

    Our government believes that Cannabis is a dangerous drug,that is why it is a schedule 1 drug.In fact they believe it is so dangerous that they are willing to bust into your house shoot your dogs if need be, trash your house,arrest you ,give you a criminal record, break apart your family because you should not be using such a dangerous drug, it’s for your own good you know.

    The government has no say in any transaction between me and a plant.

  • November 22, 2010 at 6:39 pm

    Unless there is a lot more information about this study that hasn’t been included in any of the news reports, I don’t see how it tells us anything about the effects of early marijuana use. All 35 non-control test subjects were current chronic marijuana users. The study doesn’t begin to differentiate between cognitive problems caused by current use and those that might be caused by early use. A more useful study would look at the same people after they had abstained from using cannabis for a month. Earlier studies have shown no difference between heavy, chronic marijuana users and a control group after a month’s break.

    As for the implication that early use “causes” heavy later use, where’s the evidence? If you frame this in terms of certain people being greater risk-takers than others, that explains both heavy early use and heavy current use. One might conjecture that risk-takers would start earlier and consume more throughout their lives.

    I have seen nothing in the reporting of this study that indicates evidence of “brain damage”. People who smoke 6 to 14 grams of marijuana a week, smoking 6 to 22 times a week, would never be as clear-headed as people who don’t smoke or who smoke in moderation. Give them a month without the weed and the results would be much different.

  • November 22, 2010 at 6:25 pm

    “As a nurse with 30years experience I saw too many people die too young who ahd decided to put poisons into their system. Wasn’t ever a painless death either!”

    What has that got to do with cannabis? In 5,000 years of recorded use, cannabis has never killed a single human being. As for “poisons”, cannabis is less toxic than water. You would have to smoke 1,500 pounds of cannabis in fifteen minutes to get a fatal dose.

  • November 22, 2010 at 11:15 am

    Hm. Lots of people getting very defensive makes it impossible to have a healthy debate, I think. If this was the McDonalds Happy Meal debate all over again, I wouldn’t put words like somehow in all caps to prove a point.

    At the end of the day, yes, many seriously ill people do indeed report feeling less nauseous after chemotherapy if they smoke medical grade marijuana (pretend medical grade is in caps if you like). I live in Colorado where it’s legal to use marihuana medicinally with a license as long as you pretend you get migraines. I know that prior to legalization across the board, medicinal users were an average of over 60 years old, and now they are in their 20s. Obviously, pain is a crisis/epidemic in my generation (let’s pretend that’s italics for sarcasm). Nonetheless, the intelligent choice here was legalization because there are plenty of taxes to be collected, plus the revenue from the cards sold by state is quite high I hear. It is unbecoming of intelligent people to pretend that we want to smoke medicinally. You don’t all need studies saying it’s so good for you. Realistically, we all know people who smoke a lot of weed and have rotted their teeth out, suffered from depression, gained crazy weight, and act like total losers. Those are the addicts. Similarly, we know people who smoke just before bed to get to sleep and who hold steady jobs and live good lives. We know non-smokers who are terrible at life and those who smoke once a year who are fine. It affects people very differently, and the reasons why people use it are different and indicative of their needs in life. What is irresponsible is to say weed is never harmful or addictive, because this is simply untrue and encourages continued use by people who can’t get a grip on their lives because of it.

    Much like the Happy Meals in San Francisco, I think we really don’t get to decide for anyone else what they should put in their bodies, but then the consequences of those choices are also their own. Cigarette smokers in the US pay more for health insurance for a reason. If, in the future, there are documented adverse affects from smoking weed recreationally, then will weed smokers foot those bills or should a single payer system manage those costs?

    • November 22, 2010 at 5:14 pm

      Nancy, you sound very intellgent when you belittle people’s medical problems. I am a Naval Architect and cancer survivor. I ride my bicycle 15 miles a day. I also vaporize 2 grams of what you consider to be “pretend medical grade” cannabis everyday. I was able to curb my “preted prescriptions pills” with the use of cannabis, curbing my “pretend” migranes from radiation. My job entails extreme mathmatics, canabis helps with absract mathmatics. I owe my health, defeat of cancer, my 120k salary, and my life to cannabis. You sound so narrow-minded I feel sorry for you. Cannabis has never killed anyone, happy-meals and tobacco have.

      p.s. happy meals do not grow out of the ground.
      p.p.s. you do not have to smoke cannabis to ingest it.

      • November 22, 2010 at 5:50 pm

        Hey everyone, let’s keep in mind that the original news story did not address the issue of medicinal marijuana usage which is a completely separate issue.

        Like many other studies, there are several methodological limitations including sample size and other factors.

        The crux of this research is that it basically suggests that it’s probably not a good idea for children to smoke marijuana prior to the age of sixteen.

        • November 25, 2010 at 10:12 am

          That’s the problem Jarret, this “research”, “suggests” “that it’s probably not a good idea for children to smoke marijuana prior to the age of sixteen”, without any real medical evidence. In other words, it’s nothing more than another dose of tax payer funded, anti-marijuana, fear mongering propaganda.

          “What about the kids” and untruthful/misleading allegations about dangerous driving and employees are the most exploited fear mongering points prohibitionists get on their soap boxes about but when you look at the long history of marijuana use, they simply don’t stand up to honest facts. This type of propaganda is being used to hide the honest truth.

          The government won’t legalize marijuana because timber companies, chemical companies, drug companies, alcohol companies, the oil industry and many other companies with deep pockets (largely the result of their anti-marijuana campaigns), which “contribute” to anti-marijuana politicians, fear competition from superior marijuana/hemp/cannabis products that are safer, more effective, less harmful and far more environmentally sound.

          You’re right, the original story did not address the issue of medicinal marijuana use but it proclaims that research done by “Staci Ann Gruber, PhD, of Harvard Medical School and McLean Hospital, Boston”, SUGGESTS that early marijuana use MAY be harmful, so it invites medical evidence to the contrary. No matter which issues the prohibitionists seek to try and stand on, their platform crumbles in the light of honest facts. Marijuana has been used by kids heavily during the last several decades. Where are all the brain damaged adults that have resulted? They don’t exist! If the government had any real evidence that marijuana caused ANY verifiable harms, they would have presented it long ago and in 2010 they wouldn’t be funding anti-marijuana propaganda disguised as medical research.

          The real crux of this study is a very weak attempt to exploit fears over children in order to support marijuana prohibition, via SPECULATION supported by so called “research”, bought and paid for with your tax dollars. This propaganda, like all the anti-marijuana propaganda that has preceded it since the 1930’s, is being used to enhance the financial interests of those that profit from marijuana prohibition. That’s why marijuana came to be prohibited and that’s what has kept it prohibited but as more and more voters learn the truth and consider their own experiences and/or observations they have made over long periods of time of marijuana consumers, they come to realize they are being duped.

          The bottom line is, there is no credible evidence cited in this story that scientifically supports the claim marijuana use is harmful at any age. It’s well worth debunking propaganda that claims to be medical research and educating as many people as possible about the origins, reasoning and misleading SPECULATIONS behind marijuana prohibition. As always, follow the money and you learn the truth. The folks that profit from marijuana prohibition and their motives paint a clear picture. The laws prohibiting marijuana are NOT a result of any harm from marijuana. They are the result of racism, lies and greed. Read the well documented proof of that and a lot more marijuana TRUTH in these two articles: “WHY IS MARIJUANA ILLEGAL, Pete Guither” and “MARIJUANA AND HEMP THE UNTOLD STORY, Thomas J. Bouril”, click the links to those articles on this webpage:
          Internet Explorer web browser: http://jsknow.angelfire.com/home
          All Other Browsers: http://jsknow.angelfire.com/index.html

          Considering the volumes of well documented evidence proving the many benefits of marijuana, have you ever seen even one government funded “study” exposing even one good thing about marijuana? Probably not and you probably never will until after the voters demand marijuana legalization. Once marijuana is legal you’ll see tons of positive information about marijuana like the many facts cited in the articles linked above.

  • November 22, 2010 at 1:08 am

    Watch this FL man that gets his marijuana from the Federal government destroy all the lies about marijuana consumers being lazy and unproductive. Watch him destroy all the lies about long term heavy marijuana use being harmful. Learn the truth about marijuana: http://www.youtube.com/watch?v=lvzX8aNwxgM

    One man does not prove anything any more than a few kids do but consider this: Marijuana has been used for thousands of years, it is proven safe and effective in both treating and PREVENTING a wide range of ailments, both severe and mild, without even one documented death from the ingredients in marijuana. It has been used as a recreational drug for thousands of years too and it’s far safer than tobacco, alcohol, aspirin, non-aspirin, many Rx drugs, many over the counter drugs and even caffeine, all of which can be deadly and are well documented to kill hundreds of thousands of Americans every year.

    The more voters that learn the truth the better! After they learn the truth about marijuana and the drug war 80% support rationally regulating marijuana instead of prohibiting it. Virtually all the drug war propaganda is nothing but pure lies. Marijuana does not cause aggressive behavior. Marijuana does not cause dangerous driving, Google: MARIJUANA DRIVING STUDY (remember to consider the source and the wording and read several study results). Marijuana does not cause cancer, brain damage or any serious health problems. Marijuana prohibition does not keep kids away from marijuana, illegal dealers don’t ask for ID.

    Remember the so called “study” that said marijuana kills brain cells? It turns out that monkeys were strapped down and force fed exorbitant amounts on marijuana over long periods of time through gas masks. The brain damage they experienced was NOT the effect of marijuana, it was the effect of a lack of oxygen, yet still today you hear people parroting the drug war propaganda lies claiming smoking marijuana kills brain cells and causes brain damage.

    Just look at all the successful people you read about getting arrested for marijuana, common sense should tell the average person, if marijuana did any real harm in any way, it would have shown up long ago just like the harmful effects of alcohol and tobacco have. The government has been trying to prove marijuana is harmful for decades. They started out blatantly lying and after the truth came out they switched to deceptive so called, “studies”. Just look at the wording in this article: “early users of marijuana MAY face cognitive difficulties”, “Gruber compared 35 chronic marijuana users and compared them to 28 HEALTHY volunteers (should we believe all marijuana users are unhealthy, or did they select unhealthy marijuana users?)”, Francis Jensen, MD, SPECULATES that marijuana exposure ‘is SOMEHOW modifying the way that part of the brain [the prefrontal cortex, involved in executive function tasks] is developing.” “The prefrontal cortex is one of the last areas of the brain to fully develop which MAY make teens particularly susceptible. This is not the wording of scientific fact, it is the wording used in misleading, fear mongering propaganda.

    If you want a good look at how far the government will go to promote its illegal anti-marijuana drug war message, read this: http://www.salon.com/news/feature/2000/03/31/magazines
    Several studies have concluded that ingredients in marijuana counter the carcinogens that are produced from burning marijuana. One study I read said that there has never been even one documented case of marijuana causing cancer and that tobacco smokers that also used marijuana had less instances on cancer than those that smoked tobacco only.

    After thousands of years of use and over 15000 documented marijuana studies, don’t you think the facts are well known by now? Many government studies have cited the relative safety of marijuana but rather than base rational marijuana policy in science and facts, our government ignores science and facts and promotes lies and fear mongering. On March 22, 1972 the Richard Nixon-appointed, 13-member National Commission on Marijuana and Drug Abuse recommended the decriminalization of marijuana, concluding, “[Marijuana’s] relative potential for harm to the vast majority of individual users and its actual impact on society does not justify a social policy designed to seek out and firmly punish those who use it.” Richard Nixon chose to ignore the advice of this well qualified commission and start the modern escalation of criminalizing marijuana consumers. The lies he promoted have done much harm but they served his selfish motives and got him re-elected based largely on him starting the “war on drugs”, which is actually a violent unconstitutional war against nonviolent citizens, which are no threat to their selves or society.

    In 1988, after reviewing all scientific evidence brought forth in a lawsuit against the government’s prohibition of medical marijuana, the DEA’s own administrative law judge (Judge Francis Young) wrote:

    I believe the study cited in this article is the same one I read a few days ago and have seen articles about plastered all over the internet, if so, it was funded by the National Institute on Drug Abuse (NIDA), which is well known for twisting the facts to promote marijuana prohibition. You simply can’t put trust in a so called “ study” that is funded by a government agency that depends on marijuana prohibition for much of its funding. It’s also worth noting that New Zealand research was cited as “evidence”. Read the similarities between US and New Zealand drug policies and their detrimental effects (especially on the young) here: http://www.alternet.org/drugs/90295/

    If you really want to know what’s behind all the anti-marijuana propaganda just look at the history of marijuana prohibition, then it will all make sense. The laws prohibiting marijuana are NOT a result of any harm from marijuana. They are the result of racism, lies and greed. Read the well documented proof of that and a lot more marijuana TRUTH in these two articles: “WHY IS MARIJUANA ILLEGAL, Pete Guither” and “MARIJUANA AND HEMP THE UNTOLD STORY, Thomas J. Bouril”, click the links to those articles on this webpage:
    Internet Explorer web browser: http://jsknow.angelfire.com/home
    All Other Browsers: http://jsknow.angelfire.com/index.html

    WELL WORTH READING! Free online book: The Emperor Wears No Clothes

    Cannabis Reduces Infant Mortality
    This is a great example of the information the drug war prohibitionists suppress every way they can. If babies are getting natural cannabis like substances in mother’s breast milk, do you still believe marijuana is harmful at any age?

    • November 22, 2010 at 5:58 am

      BRAVO, JSKnow, BRAVO!!!!
      I’m currently studying CBDs effects on Cancer. Imagine if people knew that it kills Cancer cells but leaves healthy cells alone. Study after study, after study… Or how it benefits people on Chemotherapy.

    • November 23, 2010 at 12:19 pm

      That was such a good comment I’m going to save it ,thanks.

  • November 21, 2010 at 8:53 pm

    Hi Jarret

    I find it interesting that those who do smoke it are coming out and getting defensive. Reminds me of the cigarette smoking debate when people would always quote their grandfather who lived to be 90 and smoked all his life! Too late that many found out it maybe wsan’t a wise choice.

    As a nurse with 30years experience I saw too many people die too young who ahd decided to put poisons into their system. Wasn’t ever a painless death either!

    The neruologists I worked with in the UK were very anti-marijauna use as they saw the effects in their hospital wards. But people will continue to do it and ignore the results. With the choice comes the consequences eh??!!

    Patricia Perth Australia

    • November 23, 2010 at 12:14 pm

      You do understand we are talking about Cannabis ,,right? Your talking about Poison,painful deaths,hospitalization,,,,I hope you are not linking that kind of rubbish with Cannabis,,,if you are please cite some FACTS.

  • November 21, 2010 at 4:59 pm

    Studies like these are invalid. One can not simply grab 35 people who have been smoking cannabis since they were 15 and conclude that since they have a low IQ cannabis is the cause.

  • November 21, 2010 at 11:41 am

    This story is bunk. I’ve been smoking off and on since I was in grade school. I have a 183 IQ, scored 1520 on my SAT, and 32 on my ACT. I’m now an Engineer with a well respected company.

    • November 21, 2010 at 12:35 pm

      Michael, there’s nothing in this story to indicate that someone with a high IQ would be incapable of scoring well on standardized tests of intelligence or completing a university degree in spite of early marijuana use.

      One study published in the Canadian Medical Association Journal, found the following association between marijuana use and IQ test scores:

      Current marijuana use was significantly correlated (p < 0.05) in a dose- related fashion with a decline in IQ over the ages studied. The comparison of the IQ difference scores showed an average decrease of 4.1 points in current heavy users (p < 0.05) compared to gains in IQ points for light current users (5.8), former users (3.5) and non-users (2.6).

      In terms of the long-term effects of marijuana on tasks such as working memory, studies have found conflicting results. With respect to the second study regarding the association between cannabis use and educational attainment, some researchers offer theories such as the common amotivational syndrome commonly referred to with marijuana use or the peer groups that marijuana users associate with.

      Previous research has found that early marijuana use is associated with an adverse impact on verbal IQ though the researchers are uncertain of the cause.

      • November 21, 2010 at 4:46 pm

        The problem I find is, the subjects weren’t tested prior to them smoking. Therefore, it makes it impossible to say that Marijuana was the cause. Given enough time, I could probably name 35 subjects that contradict the study. Steve Jobs, Carl Sagan, George Soros, (I believe) were all admitted smokers, amongst others, like former Presidents and such. From them, I would conclude that Marijuana gives a boost of creativity and intellect. The study doesn’t seem like it was well thought out, and doesn’t follow basic scientific methods. Maybe, I read into the article in the wrong contex? Otherwise, I truly enjoy your articles.

        • November 23, 2010 at 9:14 am

          Chances are those kids who started smoking earlier in life, started smoking because they were unhappy or in pain. This could be a result of childhood neglect, child abuse, or a naturally low IQ leading to poor self-esteem. Most likely the smoking eased their discomfort during the naturally turbulent teenage years, helping them accomplish more than they would have if they lived in a state of untreated depression. Those kids were destined to perform poorly in life anyway. Sad but true.

      • September 24, 2011 at 10:36 pm

        I didn’t smoke pot till Vietnam and it saved my life => I’m a yyoung 66 now !! Later in life, during a family crisis and I had cut off my pot supplier, I tried the “accepted drug” alcohol and, within 2 years, I promptly lost my wife, child, house, Mercedes, much work, etc. so, after 6 years of loss from abusive drinking, I went back to pot and not only have I not had a drink in 9 years but everything else is going GREAT as well … including being financially secure !!!! I don’t think anybody should do ANY substance, including nicotine, booze, pot, coke, heroin, speed, downs, LSD, etc till you’re 18 cuz you have to know which end is which and then, which of those “ends” is “up” before you start toying with interchanging them !!!! Drugs don’t “kill” people, people”kill” people … including their spirit !!!! It’s personal responsibility … so stop “blaming” substances cuz that’s just a cop-out !!

    • November 21, 2010 at 1:04 pm

      Prior to accepting the results…
      Read the study.
      Sample size of ONLY 40 (!) cannabis users. Talk about a flawed experiment.

      The kids who were smoking before age 16 were in all likelihood not going to be Valedictorian, judging from how they smoked an obscene amount on average.

      “I want to make marijuana seem harmful again! I think I’ll go to a run-down urban area, grab an average-sized classroom of kids with little parental guidance, and try to prove that they can’t think properly because they use cannabis.”

      I can’t wait until our governments will let us pursue honest and well-funded scientific experiments instead of pushing the fear card to advance their status quo agenda.

      • November 21, 2010 at 2:44 pm

        Hi Mcyamo, thanks for sharing your thoughts. In point of fact, it was 35 cannabis users not 40 as you suggest.

        I realize that this is a contentious and polarizing issue. On the other hand, I can’t imagine that even ardent proponents of marijuana legalization would complain that not enough kids start smoking marijuana early enough or suggest that they should start smoking before the age of 15.

    • May 8, 2012 at 5:10 pm

      It doubtful that you are as smart as claimed, or you wouldn’t care about “well respected company or capitalize Engineer. A highly intelligent person would know how to properly relate to a scientific study, what it shows, no more no less and wouldn’t write it off as bunk. It’s possible you have a resistance to the effects of THC. Pot has been historically seen for what it is, a dubious drug overall, thus Western Civiiization grew under the use of wine or beer, it would have died long ago if pot was the recreational drug of choice.
      You also may have been even smarter had you not smoked dope. You might have broke the record!


Leave a Reply

Your email address will not be published. Required fields are marked *