Marijuana’s Impact On Brain Function “Minimal,” New Study Says

[Editor’s note: This post is excerpted from this week’s forthcoming NORML weekly media advisory. To have NORML’s media advisories delivered straight to your in-box, sign up for NORML’s free e-zine here.] The consumption of cannabis, even long-term, has a “minimal” impact on brain function, according to a systematic literature review just published online by the journal Psychological Medicine.
An international team of investigators from the United Kingdom, Spain, Brazil, Australia, and Switzerland conducted a systematic review of the effects of cannabis on brain structure and function.
Authors wrote, “We reviewed literature reporting neuroimaging studies of chronic or acute cannabis use published up until January 2009. … Sixty-six studies were identified, of which 41 met the inclusion criteria. Thirty-three were functional (SPECT/PET/fMRI) and eight structural (volumetric/DTI) imaging studies. … Only three of the structural imaging studies found differences between users and controls.”
Investigators concluded, “Minimal evidence of major effects of cannabis on brain structure has been reported,” noting that marijuana users and controls perform similarly on cognitive tasks.
According to a 2001 study published in the journal Archives of General Psychiatry, long-term cannabis smokers who abstained from pot for one week “showed virtually no significant differences from control subjects (those who had smoked marijuana less than 50 times in their lives) on a battery of 10 neuropsychological tests.” Investigators added, “Former heavy users, who had consumed little or no cannabis in the three months before testing, [also] showed no significant differences from control subjects on any of these tests on any of the testing days.”

0 thoughts

  1. As a long time smoker, I can only speak of how it affected me. My once, almost photographic memory went down to a fog after three years of daily smoking. Ten years ago I stopped cold turkey after daily smoking for 15 years, and it’s taken daily supplements of fish oil o bring me back to about 75%.
    During this bout with weed, I stopped maturing emotionally and settled for stuff that I didn’t settle for both before and since. It’s like I was stuck in a place in life and didn’t realize it until I was no longer under the influence. I lost a good 15 years of my life, sitting on the couch with my head in a fog.
    I definitely do not miss it.
    Debi Davis

  2. I think that from the looks of it this was a sound experiment. Your comparing the structure of two Brains one that is high versus one that isn’t. If this is true then as we all know well enough Marijuana is nothing but a plant just like Tobacco is but has FAR LESS dangers than Tobacco. With that said, Legalize it already. Geez. Just cause we don’t grow the shit don’t mean we can legalize it and tax it. Politicians need to realize how much revenue this could potentially bring in.

  3. RE: #102 Steven,
    – It’s not really about cannabis vs. tobacco,
    it’s about the right to utilize a God-Given plant,
    whether it’s cannabis, tobacco or basidiomycetes…
    – The method of its administration, when and
    how often it’s partaken of, how it is grown,
    what its fertilized with… are stronger determinants
    of its relative danger(s) / safety…
    – Every factor considered, all of the above ought
    to be allowed, (never prohibited), be taxed and
    regulated if sold / dispensed in a retail-manner;
    – Free for one to grow and utilize for one’s self,
    (personal responsibility applies here…)
    never blame the plant-compounds / plants for
    – Some politicians think it’s a “bad idea” to
    garner revenue from what they see as possibly
    “dangerous”, “addictive” vices, merely because
    of desperate economic-times.
    – HOWEVER, bringing these “vices” ABOVE-GROUND
    allows the “dangers” to be managed more effectively
    and minimized…while availing revenue-streams
    to do so…

  4. Debi,I am not sure where you are coming from. I have smoked marijuana virtually every day for 35 years (I’m 52), have held work as a programmer, technical support technician for a larger manufacturer and an IT manager for a White Plains security and never have had my smoking cause me ANY cognitive issues. You might consider a functional MRI to make sure that your frontal lobes are fully functional. Do you drink? How does that affect your Photographic Memory? Why deny me my vaporizer? I don’t come and spit in your Merlot. Besides, why let a few facts get in the way of your anecdote?

  5. I will find a way to make this plant legal somehow i will not give up the fight i have been smoking a long time now and i know the real deal they are making me go to rehab for it now have not toked in a month i feel no withdraw but my body’s ache’s and pains have returned a nice(alt)to the nasty pills they try to shove in my mouth and i liked the no side effect cept getting hungry sometimes jesus the gov. is just down right evil the only green they know is a stupid piece of paper F*** them i won’t do what they tell me!(rage against the machine:)

  6. This studddy was goo d two weed couse it proves that I am not stuped. I now am over 50 y/o and I smoked cannabis offand on my hole life and I have quit a lott oftimes for work and whem I got kids and my wife sad “stopthatsmoking” I held lots andlots of good jobs and I work good. So sometimes I sreel smoke and sometimes I dint and I isok and have good kids that dint no I abide in it. Thankyou for putting this studdey on my pc and I hop that the govermenit getsit and leves people likeus a lone. Rock on>

  7. my story…
    when i was 11 years old i first tried weed it was pritti tasty you see and now i smoke it evryday through a bong or pipe or jus spliff either way i am high i am in school writing this rite now in ict i smoke tha dutch dutch stuff iz gd shit , i am going to try and get my friend birdy to do weed evry day in his relient robin and i wil race him in mine when i am high and he is high and it will be gd shit and then foyce will come along on a moped and get knocked of coz he is to high to ride it… it will be some quality shit and will be funny as… i am writing this because i am bored as i am going to get my mum high 2nite and feed my lil sis and bruv weed on their b days jus so they can be happy and lil bruva hu isnt even 1 yet weed and am gona make hi mdo a lung and then give the ol wolner boi a spliff on the go and go for a spin down the orad on a pedle and pop when im high and beat birdy in his relient robin. 🙂 bye bye love caz

  8. The biggest risk marijuana carries with it, is getting caught. Legalize the shit already, its just stupid, im in college and i do all my shit, deans list all day. But i get bored as hell and what better thing to do than spark up, i love the shit its the ultimate boredom killer.
    Put plainly, if you smoke marijuana your probably not going to end up going crazy, or turning into a drug addict, or join a gang.
    But you will be perfectly ok with sitting on the couch doing absolutely nothing for hours at a time.
    And you might also get arrested for it
    These are the real only dangers to marijuana.

  9. Well said, Marijuana has very little effect on over all cognition and brain function when normal users are compared to non users. Obviously there are some tendencies to be lazier or more lethargic but for some people that might actually be a good thing. As for some of the e other commenters talking about how Marijuana is a gateway drug and how it makes you want to use other controlled substances is complete garbage. The gateway argument is propagated by conservative people who view marijuana in such a negative light they equate its as tantamount to cocaine, speed, or crack use. Often times these are the same people who have never used marijuana and are ignorant on the subject in general. For more info on marijuana check out .
    All in all marijuana is a positive substance that causes more good than harm out of every controlled substance out there. LEGALIZE IT!!!

  10. Its nice to see so much information on legalization showing up in all forms online. America is closer than ever to seeing the drug war overturned.

    oh they’re sheep, my baaaaaaaaahd

  12. also
    cannabis IS a gateway drug in the sense that, once you start smoking it, you hang around with other smokers
    and people who are usually on HARD drugs usually smoke the ganja cos it helps with comedowns/feels good man and has no effect
    yeah, gateway my arse

  13. Pingback: FitMarker
  14. I disagree with some points and agree with others. After using marijuana for 6 years and then being marijuana free for the past 2 years, I can confidently say that marijuana does, (for some people) make you stupid. Iv done some brief research on the topic of ‘How does marijuana affect the brain’ and have come by some interesting points. People have stated that marijuana has made them smarter; it helps people with ADD to focus better; it makes people think more clearly when high; brings out ‘creativeness’ in some people. These are very good opinions, considering that everybody infact does react differently to this substance. As a user for 6 years, marijuana has truely impacted my brain for the worst. I have ADD, and weed made it worse. I never got good grade before I started using and I still didn’t after I started using. I could never remember any information that was taught to me in school, and I could never remember what i did the day prior to the present! Dont hold me to this, but I have heard that “the state of mind that you are most confortable in, will positively impact your performance in most activities that you do.” Therefore, if you are most comfortable in the ‘high’ state of mind, then you will perform best while you are in that state of mind. It’s a very logical opinion. Here again, everybody is different. If you study high, and take the test high, then you might get good grades. Iv tried it years ago and it did not work for me. Try it for yourself and see the outcome. On another note, marijuana does indeed help you to connect with other people that you normally wouldn’t find yourself connecting with. I dont know if it is due to the fact that two people want to get high and put their thoughts and opinions aside for the 10 min. of smoking or what, but i have definatly found myself in that situation more than once. After being drug free for two years it is safe for ME to say that I have definatly changed for the better. I am smarter now, more open minded and I have the will to WANT to learn. Before, when I use to smoke I had no desire what so ever to learn or do anything that involved education. Lets just say I learned the hard way. Now I am in college, able to read a book and interpret it, able to find out the main idea of a text, and able to do many other things that I wasn’t capable of doing before. Enough about me though, experiment for yourself what using and not using is like, and then analyze the results. You might be amazed, or you might be the same. Give it a shot, you’ve got nothing to lose.

  15. I agree that people react differently to marijuana. I believe that it depends on the person and your mind set. I didn’t do that well in school but i noticed that when i started toking, my grades increased. I would actually pay attention to classes i usually found boring. Doing lame things were less, lame. Going into work i knew what i had to get stuff done and I was more efficient. I would have months where i didn’t smoke and everything became like it was before, boring and tedious. Assignments were less of a drag to do when high, also i was more creative. This is all personal experience so might not be for everyone.
    I have found no harm and the only reason people don’t want to legalize it is cuz of money.
    What is a dollar really? It’s just a piece of paper that the man tricks people into believing it has value, when really it holds no value and is only imaginary just so the gov can keep control.

  16. ALright i have been a chronic smoker for 5 years now and I do know it has effects on me.. i have quit a couple times usually a 2 week period and i can say after this 2 week period i felt more motivated and less distracted.. i kept smoking afterwards of course i like how it makes me feel:) i can also say it is addictive i dont care how many people say its not ive probably smoked more than them beings as i smoke about 4 grams a day everyday. the side affects of the addiction are loss of appetite, (happened everytime i quit)depression, and definatly insomnia. Dont try and argue this with someone who has gone through it many times:) of course i still smoke. im recently goin 6 days sober because of a possesion charge and i have slept for probably 14 or so hours, ya not good. it is addictive it is a drug. im not saying it should be illegal like many have said alchohal and tobacco are both legal and deadly:) i had to post this, im tired of other potheads (me saying “other” because i am one:)literally lying to themselves and other people that its not addictive and that there is no harm. i personally wake up everyday coughing with flem and you people are trying to tell me thats supposedly not bad for you? its something that makes me laugh i dont defend it at all our kids probably shouldnt do it and people just need to realize ITS A DRUG! ps i gaurantee i can take a bigger bong rip than the person whos gonna try and argue with me saying pots good:)

  17. Most of you have missed an important point. The study finds no differences in subjects after the have quit using for a week. Those who use regularly may never reach this one week abstinence period are living with some effects of marijuana on a daily basis. The most significant effect will be a reduced ability to learn and remember. While this may not be an issue if you smoke occasionally, if you smoke daily for months or years, your learning over time will be significantly delayed compared to non-users. Our learning as teens is obviously very important. Missing months of years of school will have a serious impact on later achievement. Even for adults, failure to learn for years at at time will affect their quality of life compared to their non-using peers.

  18. legalize it, ciggerets are alot worse. Zero people a year die from marijuana, billions die from ciggs

  19. i have been smoking almost everyday for about 2 years now. I go to a collage prep school and get a’s and b’s in all my classes. Getting good grades has never been hard for me even no i despise school and all that it stands for i get good grades anyway to keep my parents for bitching at me for smoking pot. all and all weed enhances my creativity and it enhances my awareness. I notice how fucked up everything is and question it instead of just sitting idly by and just except things for the way they are. I think pot is natures way of telling us get up look around you what’s wrong here? For starters were wasting millions on a war on drugs , while millions are starving in the streets. Weed is the problem ,we are.

  20. i have smoked marijuana everyday for abt 9 years. at about 20 years old i started having siezures which have stayed with me through meds and testing(still working on it) i do have memory problems, pretty severe, but im not sure if that is due to the marijuana or siezures.i have only not smoked for a total of a month and a half so im not to sure if its the siezure meds or the marijuana because the memory problems started shortly after the siezures so i imagine its the meds. my husdband and many friends are avid smokers and none have the memory problems i have. the nuerologists that i have seen tell me the marijuana has nothing to do with my siezures, but does it with my memory, or is it the meds and the marijuana together? if there is anyone that is or has experienced the type of thing im going through please let me know and give me your story, thank you

  21. Okay well compare that to any long term use of anything, hamburgers, salads, t.v. umm exercise, to much of anything is bad, there’s one thing you can’t have to much of and that’s CHRIST, I say liquer and beer are worst, that’s my opinion

  22. Once again I am disappointed by the incompleteness of a marijuana study. I have and continue to read studies which describe both cognitive performance of marijuana users as well as provide information about their character and or personal lives e.g (depressed, low income, etc)
    I see no evidence of control as to strain (THC,CBD, alt cannabinoid dose)
    Altered states of consciousness need to be studies as such. We cannot compare the behavior of dosed patients to their normal sober behaviors. The change in perception or reality causes both immediate perceptual effect as well as lingering observations as the effect passes or increases. To study the cognitive effects of marijuana is like studying a differential equation of a patient’s perception of the world around them. The cognitive effects of marijuana on any patient are so grossly unpredictable and change with dose. Until we can quantify a person’s sense of “responsibility,” we are just trying to catch smoke.
    I am a 22 year old weed enthusiast who benefits greatly from sativa blends and doesn’t care much for indicas in the slightest. To say I have changed as a result of my behavior would be an understatement,but to describe the ways HOW it changed me would be presumptuous and a terrific waste of time.
    To conclude: Cognitive studies aren’t worth the time. There are all different kinds of people out there and some of them do manage to make it home from the bar without incident. Glad to know there are 143,678 studies each for and against the safety of heavy cannabis use, BUT IT WILL TEACH THE READER NOTHING about himself or herself.
    Altered states of consciousness are ALTERED and should be reviewed as such. Please!! Stop taking the word of strangers and make a decision for yourself. This is an experiential phenomenon. Gather your own data and decide for you and your family or shut up. These studies are not useful for those who have experienced the effects of marijuana and are misleading for those who do not. One more “marijuana” study and I think I may just throw up.

  23. The bureaucrats that depend upon the drug trade both legal and illegal, will never allow their jobs to end for the good of the country. We live in a plutocracy that doesn’t care about you or me, just power and all it’s trappings.

  24. What everyone really needs to realize and remember is that everything you will ever encounter in your lifetime is a mind over matter situation. This includes weed. If you let it takeover your life, like alcohol does to alcoholics or crack does to crack heads, then yes it will have some bad effects on you. But if you’re like me and you have a bowl or a blunt to wind down at the end of the day, it’s no worse than a glass of wine, a beer, or a couple of cigs. I’ve been smoking weed everyday for the past 2 years for anxiety, depression, and because I am a manic bipolar. Let me say from my own experience, that in comparison to to 3 different kinds of drugs they started off giving me the weed not only works wayyyyy better than all those damn pills but, I feel like it’s a safer alternative. Aside from that, the weed’s effects are temporary; I get through my day as a mom a wife and a full time legal assistant, then I usually smoke every night before bed, chill on my high for 2 hours and go to sleep. I do not have issues with learning or remembering any more than the average busy mom/wife, and MJ actually helped get me through law school, on a B average nonetheless, so anyone who bad mouths weed saying that it makes people more stupid, is ignorant. I don’t let weed run my life and it has been nothing but beneficial to me. Like I said it’s mind over matter.

  25. One more thing; The mind over matter stuff applies to the debate on whether MJ is addictive as well. I personally don’t think it is, but I rely on it for mental illness, so I won’t debate anyone on the topic of addiction.

  26. I’ve been smoking marijuana for the past 20 years. No more for me. Over the last two years I have developed severe fatigue,memory loss,concentration problems, loss of appetite and weight loss, muscle and joint pain, sore mouth and throat. I’ve lost interest in things that were extremely important to me.
    With all the chemicals added to pot, I feel, I have been “poisoned”, you might say, by said chemicals added to pot. Comments are welcome, Be careful.

  27. Well this has certainly been interesting, mostly because the people who seem the most militant about how great mj is are also the ones with the most grammar and spelling issues. This is making me rethink my position of supporting mj. I have smoked for over 25 years but I am no longer so dishonest as to pretend it is harmless. When people say pot is less harmful than some other mood altering substance they have already lost the argument but are too high to understand why. It’s like saying a bomb is more deadly than a gun. That is not a viable argument. The fact that so many people have had a negative experience with it is sufficient reason to NOT present it as “harmless”. People do not suffer from things that are harmless. The fact is that there are 8,000 people a year that go to the emergency room because of what they feel is a marijuana overdose. I was shocked when I found this out. I was convinced that was not possible. I have a high school friend who is an ER doc that told me about it. When he and I were remeniscing about school I was struck by the fact that in school we were about the same academically speaking but now I have been breaking my back swingin’ a hammer for 30 years and he’s an ER doc. And, you can guess which one of us only smoked a couple of times in high school and which one of us made a career out of it.

  28. Smoke weed everyday!!! No but really have fun, smoke weed – just don’t do it everyday otherwise you’ll end up like me – a turd burglar

  29. It’s all about how you let it effect you. I have smoked weed everyday for three years. I work 40 hours a week as an insurance salesmen. ( youngest person in the company)I have the best meomory by far out of all my friends and has been effected very little by my marijuana use. However, alcohol has caused me to forget whole night of my life. If the worst thing that is going to come from the daily use, is that everyonce in awhile i am going to forget where i put my keys then i am cool with it. The people who let pot run their lives and can’t get off the couch, are just lazy and use the MJ as an excuse and a crutch. It doesn’t matter how much you smoke, if you want to be successful and you work hard than you will see very little negative effects from it. Also even if it’s not harmless or non- addicting it’s still far less than basically every other substance.So for those of us that need a little help in our day ( which from coffee to heroin almost everyone does ) marijuana is the best option.

  30. My story… Marijuana is a drug, but its less harmless then smoking tobacco or drinking alcohol. I have been smoking since i was a 14 and been smoking for 3 years now. I have had an overall 3.0 gpa throughout highschool I have been playing baseball since I was 5 and it has not effected my school work or my sport. The one thing that I dont like about smoking marijuana is the effect of muscle growth and the making of muscle which is decreased. Unlike most people on this blog I have not experienced memory loss (short term). and for the last person above you cant overdose on cannabis its been proven, also for your friend the ER those people who came in for thinking they overdosed they were having anxiety issues

  31. I am 52 years old, and have been smoking Cannabis for 37 years. From my experience, it has not caused any problems for me at all. I can still “run the categories” on Jeopardy, and have never had “cravings” for it when not smoking for extended periods. One study I saw out of Europe stated that Cannabis smokers had less chance of getting lung cancer than NON SMOKERS… that is people that have NEVER smoked ANYTHING(tobacco, etc.). The reason for this is Cannabis has regenerating qualities especially in lung tissue. It helps the alveoli(air sacs) keep their elasticity. Also studies have shown that it delays Alzheimer’s disease in those hereditarily pre-disposed to the condition. I have a insomnia and RLS. I also have a father that died with Alzheimer’s and Dementia. I also smoke tobacco, which I readily admit I am addicted too. Cannabis is the best fix for all my conditions/situation, yet it is illegal for me to obtain, grow, or use (SC). I am MADE a criminal and have to deal with seedy people to obtain my medicine. It is ridiculous. Alcohol is legal. The time has come for National Legalization at the Federal level.

  32. ive been smoking weed for just about 7 years straight. for years it was allday everyday. it was my mission, wake up, get high, rinse and repeat. over the last year or so, negative effects have become more and more apparent. cognitive impariment. difficulty with memory, anger, cravings, and as of late.. paranoia when i smoke. my heart will start beating quick and even when im sober.. my thoughts have become oddly paranoid. i will say, i dont believe that pot affects many people this, but for me.. it did. and yet i still struggle with smoking it. for me, its more than a mental addiction since its been such a part of me for so long now. i believe it helps some, and hinders others. it should be everyones own right to decide whether or not they smoke, but i think ppl should be more aware of the negative effects it has when starting young.

  33. If pot has become “part of who you are”, then this is a psychological addiction and you are not objective enough to comment on how it physiologically affects yourself or others.
    If you are unsure of why you are behaving a certain way, you are setting yourself up for disaster when some authority arrives and convinces you that your behavior is wrong (authority could be anything, a doctor, parent, even your own conscience). That can be applied universally. Instead of admitting a weakness of character, it is FAR easier to pass the blame on to the behavior and condemn that, so your ego need not suffer.
    “Know thyself, know thy enemy, a hundred battles, a hundred victories.”

Leave a Reply