Getting high on a regular basis as a teenager has been said to lower your IQ—but the truth may not be so simple.
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Cannabis rots your brain — or does it? Last year, a paper published in Proceedings of the National Academy of Sciences (PNAS) suggested that people who used cannabis heavily as teenagers saw their IQs fall by middle age. But a study published today — also in PNAS — says that factors unrelated to cannabis use are to blame for the effect. Nature explores the competing claims.
What other factors might cause the decline in IQ?
Ole Røgeberg, a labor economist at the Ragnar Frisch Centre for Economic Research in Oslo and the author of the latest paper, ran simulations which showed that confounding factors associated with socioeconomic status could explain the earlier result. For example, poorer people have reduced access to schooling, irrespective of cannabis use.
Is this a case of correlation versus causation?
Possibly. The data used in the original paper came from the Dunedin Study, a research project in which a group of slightly more than 1,000 people born in New Zealand in 1972–73 have been tracked from birth to age 38 and beyond. As with all such birth-cohort epidemiological studies (also called longitudinal studies), there is a risk of inferring causal links from observed associations between one factor and another.
Past research on the Dunedin cohort shows that individuals from backgrounds with low socioeconomic status are more likely than others to begin smoking cannabis during adolescence, and are more likely to progress from use to dependence. Røgeberg says that these effects, combined with reduced access to schooling, can generate a correlation between cannabis use and IQ change.
According to Røgeberg, people with low socioeconomic status are, on average, likely to show declining IQ as they age and gradually self-select or are sorted into less cognitively demanding arenas. For example, they are less likely than people with high socioeconomic status to attend university, and more likely to take manual jobs.
Do other studies show a drop in IQ with cannabis use?
Røgeberg cites three studies in which cannabis use is not associated with declining IQ. He says that these studies show clear reductions in IQ for the heaviest smokers, but these are not permanent, and people who have stopped smoking heavily show no decline.
What do the original paper's authors make of Røgeberg's analysis?
Madeline Meier, a psychologist at the Duke Transdisciplinary Prevention Research Center in Durham, North Carolina, who co-wrote the original paper with her colleagues, says that Røgeberg's ideas are interesting. However, she points out that the authors of the first PNAS paper restricted their analysis to individuals in middle-class families and those with low or high socioeconomic status. The outcome suggests that the decline in IQ cannot be attributed to socioeconomic factors alone.
In their original analysis, Meier says, she and her colleagues controlled for socioeconomic status and found that in all socioeconomic categories, the IQs of children who were not heavy users remained unchanged from adolescence to adulthood. Therefore, she says, socioeconomic status does not influence IQ decline.
So who is right?
It is hard to say. Both analyses study the same data set in different ways, and each has merits.
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49 Comments
Add CommentHypothesis: It is obvious that (1) big pharma's unquenchable need for profits and (2) the interaction with the religious/conservative cooks with lower IQs to start with, are the two totally uncorrelated factors that cause the fetid-heads to loose their marbles as they grow old. (But they do start with an edge and consequently have more fun - apart from a higher propensity to suicide, yet another unproven yet etched in stone hyposthesis.
Reply | Report Abuse | Link to thisI don't need a study to know that when I smoked pot I lost my mental clarity and sharpness and my ability to form memories suffered as well. If you do not value a sharp,clear,fully functioning brain, then by all means toke up.
Reply | Report Abuse | Link to thisWhat is genuinely dumb and dumber is the federal government's listing of marijuana as in the same class as narcotics, though no one ever overdosed on marijuana.
Reply | Report Abuse | Link to thisIn spite of this, many cancer patients suffer needlessly from nausea and lack of appetite while undergoing chemotherapy. A genuinely modern, scientific and humane approach would be to consider marijuana a valuable medicine for treatment. Instead, we are offered a moral platitude about pot making you stupid. The reality is what makes you stupid is mostly the sniffling ignorance that pervades our culture. Looking down on a harmless weed only provides greater evidence of the mass stupidity.
There is a way to prove, once and for all, whether weed impacts IQ. And longitudinal studies comparing pot use to IQ aren't it. I mean, all this social science is great and all, but "does weed impact brain function" is not a social sciences question. It's a biology question. So let's try studying some biology.
Reply | Report Abuse | Link to thisAll you have to do is find the actual mechanism that causes neural degeneration in pot smokers but not in those who don't partake. In the meanwhile, since there is no conclusive evidence that pot smoking is harmful, and there are mountains of conclusive evidence that the policies of pot prohibition ARE harmful, let's legalize it, tax it, and then spend the sudden and overwhelming budget surplus on fixing the economy and, oh yeah, mounting a scientific study that will actually answer the question!
Or drink! Eh?
Reply | Report Abuse | Link to thishuh? wha? whuuuh.
Reply | Report Abuse | Link to thisI have to admit I smoked pot heavily back in the 70's when I was in college and it hasn't impacted my intelligence any worse than listening to FOX News for an hour...
Reply | Report Abuse | Link to thisThis is all misses the point. Does ANYONE doubt the risk in inhaling smoke no matter what the source. Tobacco, weed, paper. Let stop splitting hairs. There is no evidence that will convince potheads that they are injuring themselves and endangering others.
Reply | Report Abuse | Link to thisYes, *while* you are smoking regularly, there does seem to be a reduction in mental clarity and short-term memory, but the study has to do with long-term effects that had previously been reported as manifesting well after regular pot use - and *that* is what the article is suggesting may not hold true.
Reply | Report Abuse | Link to thisOr we could just ask my old boss, Willie N. He will be 80 next April. I'll be 70 in May. We're both still kicking.
Reply | Report Abuse | Link to thisLife is short. Why would people want to drift through it in a spaced out fog? Back in the day I used to think pot was cool, but then when I finally quit I was totally amazed at how much better I felt: emotionally, physically and mentally. I had my mind back and I knew it, and it was an incredible feeling----WOW. I'll never go back to pot.
Reply | Report Abuse | Link to thisYes, heavy long-term pot use will possibly cause emphysema; but there is no link to lung cancer. Meanwhile, pot is a stress relieving medication, and stress is most likely the number one cause of most illness- in all species, including our own. So, one could argue, and there may already be science to suggest or prove it, that pot smoking actually improves one's health.
Reply | Report Abuse | Link to thisNow, we can discuss the obvious link between pot use and creativity and higher consciousness. You can thank pot and other psychedelic drugs for MUCH (possibly most) of your dvd and cd collection.
It will be legal soon. The tide has turned, the war is over. All hail- freedom!
I hereby volunteer for the study. I would be a good candidate :)
Reply | Report Abuse | Link to thisOne of the main factors not mentioned in this article is the developing teenage brain, in particular among males whose front lobe is not fully developed until their 20's, if not later. This area is not fully formed and is very vulnerable to drugs, in particular alcohol, which can damage these sensitive nerve connections. Marijuana, while I have nothing against it personally, can also have a negative effect on these synapses during this critical time of development.
Reply | Report Abuse | Link to thisI am an engineer, I'm 64 years old & I've been smoking pot since I was 18. I'm at the top of my field, and have been for 27 years. All of this "research" is a joke.
Reply | Report Abuse | Link to thisIt depends on the strain you're smoking. If you don't like feeling dumb, try Sativa.
Reply | Report Abuse | Link to thisWe didn't need a study to know that. Inhale to all.
Reply | Report Abuse | Link to thisNot everyone responds to it the same way as you. For other reasons, I too stopped, but neither myself nor any Marijuana smoker I currently know "drift through [life] in a spaced-out fog". Some years I ago I was acquainted with some party-kids who lived that way, but it was hardly *just* the Marijuana that led them to be so; it was actually their whole lifestyle choice. There are plenty of high-functioning pot smokers.
Reply | Report Abuse | Link to thisBack when I was in college they had this thing called beer, if you drank enough it made you forget what happened during the period called "drunk", sometimes people would get "drunk" and go get in fights, or worse skin your knees!! I remember those times because of being drunk I was high.
Reply | Report Abuse | Link to thisI have no doubt that pot smoking reduces I.Q. In the same way that I have no doubt that watching Fox News or reality TV reduces I.Q. The reports do not say to what extent scores were reduced or compared those score to such mundane activities as listed above. The fact is that there are too many interrelated environmental factors over decades that could contribute in whole or in part to these numbers. Personally, my high school grades increased dramatically after smoking pot. My law degree would go against the conclusion that you turn into the unwashed proletariat once you have touched the evil weed.
Reply | Report Abuse | Link to thisWhy not just avoid all psychoactive drugs? Whether THC is harmful to the brain or not, smoke of any kind is bad for the lungs. Now, there are alternatives to smoking marijuana, but I know from experience that many pot smokers are too lazy to change their habit.
Reply | Report Abuse | Link to thisSo, given the studies cited, smoking dope may reduce IQ and extended breast feeding probably increases IQ, what's a 50's baby-boomer who wants to get high to do? Seems clear to me....
Reply | Report Abuse | Link to thisCannabis products, and there's a lot of it, from joints to pastries to capsules, have no known safe use with ample medical indications, Cannabis induces serious psychosis, and the early you start smoking Cannabis, and the higher your consumption of Cannabis products is, the higher your chances of becoming schizophrenic. And old Moroccan adage states: "A bit of hashish warms, a lot burns", and some earlier users as the french writer Charles Baudelaire said that Cannabis stimulates imagination, but destroys will.
Reply | Report Abuse | Link to thisyea, I doubt it and there are no facts to back up your claims of endangering others, nor harm to the individual, There are a dozen things in your home more dangerous.
Reply | Report Abuse | Link to thisIt is a restriction of freedoms at the best and the last bastion of idiots at its worst, start worrying about my decisions that don't effect you.
I wonder about this: if marijuana use affects metal clarity, and an ability to form memories (as it *seems* when under the influence) then wouldn't it have a profound affect on young people using who are in their prime learning years? Even if somehow it didn't show in IQ, would it not affect the quality of their learning? Might it also affect their motivation for continued learning, or just the paths they may choose? Might it also affect their experiences - brushes with the law - and thus their futures. These studies are perhaps important, but IQ is not a sole determinant of, well, much, right? I think even for the purpose of policy planning, all outcomes are relevant, not just IQ. Although I suppose you would have to control for issues regarding it's legality to get a true measure of the influence of the substance alone.
Reply | Report Abuse | Link to thisIt's funny that the link only provided the Abstract. I would have especially liked to have seen the Method section. The abstract did not mention IQ testing, but instead referred to "neuropsychological" testing, which implies a lot more than an IQ test delivers. Did they directly observe any neurological damage? IQ as measured by which IQ test, as IQ tests used to measure individuals under 21 and over 21 should be different. Personally, I'm skeptical of any study that uses IQ as its dependent measure, because IQ is more of a statistical artifact than anything else. If you want me to believe that smoking pot directly harms the brain - show me the actual physical damage. It's been done with alcohol studies.
Reply | Report Abuse | Link to thisWe live for poignancy and weed is poignancy obliged.
Reply | Report Abuse | Link to thisAmen to that!
Reply | Report Abuse | Link to thisEverybody knows by now that smoking is very harmful to your health. It is quite obvious that you will shorten your life by smoking and it does not matter WHAT you smoke. So, pot smokers, on average, will die sooner than non-smokers. I think that is all that really matters.
Reply | Report Abuse | Link to thisPot Smokers: Dr. Carl Sagan, Richard Branson, Ted Turner, Aaron Sorkin, Steve Jobs, Jack Kerouac, Barack Obama, Bill Clinton, G.W. Bush, Stephen King, Arnold Schwarzenegger, Michael Phelps, Michael Bloomberg, Louis Armstrong, Kareem Abdul-Jabbar, Usain Bolt, William F. Buckley, Richard Feynman, and perhaps our most revered and holy Priest of the Ganja Bud: Bob Marley.
Reply | Report Abuse | Link to thisHistory will long remember all the above people, and history will soon forget the clowns who post here about the evils of Love Grass. Ganja doesn't destroy the mind, ganja OPENS the mind to new perspectives and new points of view.
Pot will always be controversial. People that think pot is evil should simply NOT ingest it. People that enjoy pot should be allowed to do so LEGALLY. I am VERY happy Colorado and Washington state are now taking the proper steps toward full legalization of ganja. It is simply a travesty that 60,000 Americans are currently in prisons and jails for pot related incidents. This insanity must STOP. Pot needs to be removed from the DEA's schedule I narcotics listing NOW.
'Dosage makes the medicine'. Let's look at this in a slight objective way by accepting the the subject of it, pot interference with biological systems, is both determined on some sort of fundamental reality and statistical on occupational 'level'.
Reply | Report Abuse | Link to this1. Today, intelligence has been measured via pattern identification, reasoning, and to some extend creativity.
2. Increase of usage increases tolerance as a process of 'adaptability'.
3. It matters what one feeds up brain with: from a developing brain to mature consistent one, over to functionally declining one. It that sense perturbations are essential as long as observations are being within composed matrices of observations. Pot usage may extend one's computing time (decision making process), however, it may increase an abstract formation ability.
4. In many cases alcohol related car incidents are far exceeding that pot related incidents. That is because alcohol makes you drive fast and fearless, while pot makes you being cautious about it.
5. Drugs that stimulate brain activity time wise (white powders much used for) are a lot more harmful in a long term.
6. Pot amplifies one's condition and tendency of thinking over. That is making happy people happier and sad people sadder. In that sense mind occupation is crucial.
7. Legalizing processes shell take all accounts on scientific grounds by proper authorities and measurement techniques.
8. All tax payers money must go towards research and job occupation of bio processing that has a sustainable tendency environmental wise.
9. Obviously The Lancet serves interests of a drug industry supporting a certain domain of addict-ability. It is known that UK leads in heavy drug addicts "The Lancet has taken a political stand on several important medical and non-medical issues. Recent examples include criticism of the World Health Organization, rejecting WHO's claims of the efficacy of homoeopathy as a therapeutic option,[5] disapproval during the time Reed Exhibitions (a division of Reed Elsevier) hosted arms industry fairs, and a call in 2003 for tobacco to be made illegal" Let's see, who profits from illegality - ??????????
10. What about meta - amphetamines and all other synthetic drugs ? "A December 2010 article determined that alcohol had the worst medical and social effects compared to other recreational substances such as heroin and crack cocaine" - Who is Lancet?
Yeah! those people may have smoked Cannabis, but how many cigarettes or joints or whatever you may like calling it a day, and from what kind of herb?. There are high differences in the amount of active components from batch to batch, and also for how many days a week, and for how many months or years did you smoke makes a difference in the damages you may suffer; just from a lung function tests impairment point of view, Cannabis is worse than tobacco; if you smoked just one, and "didn't inhale", as the active products in Cannabis need to be activated in the liver, and it takes a time and repeated dosing of the product to have the system running in metabolizing the Cannabinoids, if you smoked just one joint, very probably you've smoked nothing. The feeling that your mind is clearer and more clever on the drug is a delusional feeling, close to an hallucination, it appears also with even more dangerous drugs, as LSD, and is a delusional component present in psychosis not related to drugs. It has been measured, Cannabis does impair your driving performance, and the higher number of accidents in which alcohol use is present respect to those Cannabis had a participation may just reflect the different number of users, and of heavy users, of both types of drugs of abuse.
Reply | Report Abuse | Link to thisHere's a challenge I like to throw out, so far with almost no results. Have someone who is NOT a pot user write in and tell us how they have seen that using pot makes you more intelligent, a better person, or more creative. The only answer I ever got that was even remotely pertinent was someone who related how a friend, who used to be a violent drunk, didn't get violent any more after switching to pot.
Reply | Report Abuse | Link to this"Pot amplifies one's condition and tendency of thinking over. That is making happy people happier and sad people sadder. In that sense mind occupation is crucial. "
Reply | Report Abuse | Link to thisWell, I'm sold.
If your older and normally educated it has no discernible effect. I have seen serious smokers go on to very successful careers. It seems to depend upon the individual. There are folks that should never take anything. You really can't do serious work or problem solving when stoned. Just as you wouldn't do well equally drunk.
Reply | Report Abuse | Link to thisThe entire argument lacks any sound research. Very important to check the IQ of those doing the research.
I'm with you, theaterlon! I'm seventy seven and I've been smoking reasonably regularly since about the late 1950's. That's well more than fifty years. I have also had a satisfying career in a technical area of science.
Reply | Report Abuse | Link to thisI have found that I have had some really good insights when smoking. However, my writing when stoned lacks concision and can wander. So, I polish up my writing when not under the influence. But, pot can definitely unleash creativity.
I have no major health problems due to pot. I have published two books and am working on a third since my retirement, as well as some chapters and other articles. Of course, you don't want to attend high level conferences, give lectures or definitely not teach a class while stoned, but in its place it is both pleasurable and helpful.
Here here!
Reply | Report Abuse | Link to this29. Mykeljon1
Reply | Report Abuse | Link to this12:01 AM 1/16/13 writes....
....Everybody knows by now that smoking is very harmful to your health. It is quite obvious that you will shorten your life by smoking and it does not matter WHAT you smoke. So, pot smokers, on average, will die sooner than non-smokers. I think that is all that really matters.....
People who regularly travel in an automobile can expect to have shorter lives on average than people who don't. I guess that is all that really matters.
Astronauts who experience extended stays in orbit will have shorter lives than those who maintain similar healthy lifestyles without the prolonged space exposure. I guess that is all that really matters.
there is no truth what so ever that smoking skunk long term(WHAT WAS I SAYING)oh yes,makes you paranoid,(i,m writing in the dark,i know they are out there,or forgetfull or lowers your IQ.
Reply | Report Abuse | Link to thisWHAT?
Reply | Report Abuse | Link to thisYou got my vote. Tax that junk and do real and meaningful research with the money.
Reply | Report Abuse | Link to thisSmoking cannabis ganja clearly has no adverce affects upon ones' intelligence quotient. For 14 years from 1992 to 2016 i smoked ganja two times daily and would head straight into essayist journalism from there. i would write 11 essays per day. Then in 1996 to 2013, i became a magician who studied creationism through spell casting. And just considering that i have a subscription to the scientific american journal indicates that i have no aversions to the ways of the intellect.
Reply | Report Abuse | Link to thisyes, as you said, there is indeed no evidence, none at all, that could convince people that cannabis ganja is harmful.
Reply | Report Abuse | Link to thiswell, prohibiition of cannabis ganja causes brushes with the law that harm ones' legal standing and thus other socioeconomic standings. but people who engage in the harmless ganja and the society around them do not need these brushes with the law, especially as these are people who on the whole do no harm to society in ways that need law enforcement. Prosecute real crimes instead of scapegoating harmless people and their habits. would you criminalize poverty, and arrest people without enough money, because these are people more prone to stealing property?
Reply | Report Abuse | Link to thisas of 20 years ago, there were 10,000 studies done on pot through history, and none proved any adverce effects upon life expectancy nor longevity.
Reply | Report Abuse | Link to thisResearch studies can show whatever the tester wants shown because most research has bias in it. Meir shows no drop in IQ among users and Rogeberg shows a decline in IQ although both controlled for socioeconomic status. I feel that Rogeberg would be right.
Reply | Report Abuse | Link to thisSBynum
The only problem is our lack of knowledge on the endocannabinoid system. The system was only found when we took a look at how THC works. Its the third bodily communication system, the other two being Nerveous system and the endocrine system. The nature of the endocannabinoid system makes it hard to detect. We put immense effort into trying to explain how acetaminophen/paracetamol works like the other NASAIDs dispite its different properties. We only found it worked on CB receptors when we looked at how weed causes its effects. THC has been studied a lot, but there are over 80 other cannabinoids in cannabis alone. The chemicals themselfs decay and turn into other cannabinoids, and the methods of consumption such as smoking has uncountable effects. Different temperatures make for different chemical reactions which throw in even more variables.
Reply | Report Abuse | Link to thisWe cant even properly rule out a lot of the cannaboids due to not being able to pass the blood brain barrier, because of their unique properties. All cells in the body have cannaboid receptors. Endocannaboids are synthesized as they are needed, with mostly very short half-lives so are impossible to detect unless the circumstance for their release is met. The range of the canaboids is very local. The body uses the endocrine or nerveous system for long distance or full body signals. The signal can seemingly travel like a wave, with cells acting as routers in a sort of cascade effect. The blood brain barrier might stop blood-borne transmitters, but the endocannabinoids can use juxtaposition of cells to travel.
The endocannaboid system in my opinion, a critical part of how the mind works. Current neuroscience cant explain the mind. It shouldnt exist in the way it does. We have found anandamine, one big components of our appetite+hunger only recently because THC is an analog. Mark my words, discoveries about the Endocannabinoid system will bring forth a lot of new, revolutionary medications. The ignorance to research on cannabinoids due to Caannabis's use as a recreational drug has been incredibly harmful. The recent increase in its study has verified there is something to a lot of the claims to cannabis's health benifits, which are contradictory to the old studies that were used in the justification of illegalization. The safety levels shown are amazing compared to current medicine.
ADHD in particular I feel will have breakthroughs in replacing the amphetamine medications with safer alternatives. There is a different affect on people with ADHD than there is normal people
"the authors of the first PNAS paper restricted their analysis to individuals in middle-class families and those with low or high socioeconomic status"
Reply | Report Abuse | Link to thisMiddle-class, low and high socioeconomic status... What's left out? I don't see where the restriction is.
I think this is just an excuse that can legally sell marijuana. Let's switch to another side: if cigarettes are made of marijuana, will we still have the sign of "smoking may cause lung cancer" or similar " smoking may cause brain dead" ?
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