BSIP/Photoshot
Getting high on a regular basis as a teenager has been said to lower your IQ — but the truth may not be so simple.
Cannabis rots your brain — or does it? Last year, a paper published in Proceedings of the National Academy of Sciences (PNAS)1 suggested that people who used cannabis heavily as teenagers saw their IQs fall by middle age. But a study published today2 — 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 labour 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 shows3 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 studies4–6 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.
Is there a way to find out the answer definitively?
Perhaps — by comparing the Dunedin Study with another in a different country. Such comparisons have been done before. For example, the United Kingdom's Avon Longitudinal Study of Parents and Children (ALSPAC) found that children who were breastfed for longer went on to have higher IQs, lower blood pressure and lower body mass indices than those who were not. However, longer breastfeeding is associated with higher socioeconomic status in the United Kingdom; when the data were compared with data from the Pelotas longitudinal study in Brazil, where breastfeeding is not associated with higher socioeconomic status, the link with increased IQ was maintained, but the other benefits disappeared7.
What do other scientists think?
Mitch Earleywine, a psychologist at the University at Albany, State University of New York, says that Røgeberg's analysis definitely supports the idea that links between adolescent cannabis use and drops in IQ are essentially spurious, arising from socioeconomic differences rather than any sort of pharmacological action. John Macleod of the University of Bristol, UK, who works on the ALSPAC data, points out that Meier and her colleagues acknowledged in their original paper that the results might be caused by confounding factors. He adds that the modelling in Røgeberg's paper shows that within a set of reasonable assumptions, this is indeed possible.
- Journal name:
- Nature
- DOI:
- doi:10.1038/nature.2013.12207
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. Fairground Hire
It is hard to say. Both analyses study the same data set in different ways, and each has merits. Conveyors will use what you said.
Case-control studies show that light to heavy cannabis use can cause enduring neuropsychological problems, but they are retrospective and there are no tests of premorbid functioning. Studies reveal that the misuse of oxyelite pro also reduces IQ
Dr. Madeline Lenes
Medical and recreational marijuana may be legal in many parts of the world, but I don't want to use such drugs. Shutters Folkestone is the best place for me.
We should stop such things in my opinion. I saw that TV aerials London have a campaign against such things! I am sure that with some new laws and a better strategy we can do it.
Yes, 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 lipo 6 black ultra
With the Test X180 relies on well-researched natural testosterone boosting ingredients such as Testofen®, which can significantly pump up a person’s free testosterone levels. Download filmes the product has no harmful side effects and has been shown to deliver improvements in strength and endurance in just days. In fact, the company states that results of Test X180 include enhanced physical performance and stamina.
I know what you mean, but maybe with the Edmonton Seo we can save some of them. At least that is my personal opinion and maybe we should try it. What do you think?
People always tell me I am kidding them till I shown them the medical files of my father's brain in a CAT scan from a Dr. Adlson which concluded that the holes in my father's brain were from prolonged use of pot.
One Medical Case, and one Diagnosis from one doctor for your father ( my sympathies ) doesn't conclude that the use of marijuana can do permanent damage in users. It would take much more extensive case studies. I would be interested seeing the journal articles and case files you mention. Can you provide links?
Though, question. Did your father use in his adolescence--like a lot?
Decades ago Discrete Scale Relativity predicted that the proton radius would equal about 0.81 fermi, based on the Schwarzschild metric and the corrected value of G. Going to the more realistic Kerr-Newman metric gives a slightly higher value of 0.814 fermi.
Dr. Olegary Mussul
Works: agencia de modelos
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. Improvide with herbalife
All 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!
people who used cannabis heavily as teenagers saw their IQs fall by middle age.
Jct: That would explain the successful careers of President Barry "Shroomer" Obama and his pot-smoking friends. Ever since U. of Saskatchewan discovered in 2006 that cannabis promotes brain cell growth (the reason it's good for Parkinson and Alzheimer's), I too have come to the same conclusion that new brain cell growth must make IQs fall! Har har har har har har.
This website amazing with top quality articles! I am sure that we should apply what you said above about it! With a better strategy we can change many things!
The argument, described in the article, is probably a statistical one. The key paragraph in the economist's letter to the authors of the cannabis study (https://docs.google.com/document/d/1cdtDZom_6Syn7LBs5quT80auk0NhxyR9YCJOa1yC9IE/edit) is the following:
"More importantly, as I note in my paper, this method of controlling for confounders is problematic: Using this method, they can establish that none of the confounders examined can single-handedly remove the entire effect they have found. However, we would need to include the full set of confounders simultaneously in a multivariate model in order to assess how much they collectively contribute to the measured effect. This is – as far as I know – not yet done. It is important to note that such multivariate analysis is by no means particularly complex or advanced, and is easily performed using any standard off the shelf statistical package."It looks like that all they need to do now is to form a regression model with various socioeconomic factors included in order to prove who's right... I am kind of surprised why all this (public) writing between researchers has to take place when the solution seems to be relatively easy.
Hi,
The neuregulin family that act on the EGFR family of receptors specifically the ErbB4 receptor seems to be the reason. Susceptibility genes for cannabis dependence has already shown that it has a strong genetic component indicating an only affected group, so not everybody.
@John Patrick but isn't everyone who had a cavity filled over 10 years ago and who has drank faucet water been exposed to both mercury fillings and fluoridated water? That wouldn't explain the supposed decrease in IQ in solely those who habitually smoked pot
Coming from the field of law, I can assure you that the people who need a criminal lawyer particularly for things like drug crimes come from all walks of life and socioeconomic backgrounds. I knew people in college who were very high functioning smokers. They went to class, did well and have great careers now. However many were not so fortunate. I'm not so sure about lowering the IQ, but I do know those who I knew habitually smoked did seem to become more indifferent and less themselves- with less excitement about life.
i believe that fluoride in the water and mercury in teeth can also cause this decline. were they factors in study?
The fact that THC causes neuro-genesis offsets any short term memory loss. 4 weeks after THC is consumed new neurons are formed giving the user much more room of which to operate within. Sure while high a user's Hippocampus has been effected, causes some short term memory loss, but nothing permanent at all. The benefits far outweigh the negatives, which from my pov I don't see any if you vaporize or eat it.
My theory is it effects short term memory, but not long term. I used to know some papers to back this up, however do not wish to track down things from 20 years ago. I would love to see some biochemical studies on this. Observing pot smokers in their native environment, they forget things for the 20-30 minute period, but have no problem with recall an hour later or days, etc...it has something to do with immediate recall. Most of the other things are usually biased, such as the 1970's paper on pot smokers having increased female hormones such as estrogen, and developing female traits funded by the anti drug policies of the US government put out by Then president Nixon. But lack of access to real biological studies is a problem as most funding acquired for any biochemical pot (or THC's 1-30) are funded by agencies with a strong desire for biased outcomes (that would I am sure, and have seen in non-scintifics folks statistical analysis, but lacking degree's they receive zero weight, although MS excel and Scidavis or qti plot have most high end statistics to do combined paper analytic s, even coupled with words, phrases, or any variables one desires.) It does make people preform better on some types of IQ tests, however with longer time periods (more correct puzzle assemblies, but longer times) so what to make of it. Other studies showed people were on test driving ranges less likely to crash, but often would miss a turn point and drive around one more time, but the accident level was dictated by the non-intoxicated persons desire to perform the test under disciplined conditions.
My generation slightly preceded the '50s and '60s hippy drop out era . Born 1934. I entered the motion picture labor pool and realized Hollywood was driven by alcohol. It was very routine to make an alteration during the shooting day to accommodate an intoxicated participant. Be it a movie star, director, or truck driver.
But strange, until they reached that state, their decision making process was full of vigor and was not an encumbrance to the filming process. Until their actions became dangerous.
But when marijuana entered the film industry full tilt, it was hard to plan a day because such a state of intoxication resulted in a, "what's the rush?" attitude.
My occupation required clear thinking, planning, and precise execution. Not only for the film quality, but to protect against injuries.
I realized very well on that those persons whom I knew to be doing a “toke” now and then during the film day could not be relied upon for responsible judgments. They were in a very exact sense, “happy”, and not totally involved.
This behavior would appear to be a lowering of IQ performance. But to my observations, the IQ was functional, but the dedication and commitment was lacking.
They did acquire though, a sense of superiority over most situation. And this is where the impairment was very obvious. In most cases they became inept.
Ray Tostado