Source
r/DrugNerds•
Entropless

Long-term cannabis users showed IQ decline from childhood to midlife (mean=−5.5 IQ points)

Today is 420.

However let's use it as a reminder, that cannabis is not harmless. It can, and will, make its users stupid in the long term. If you are still going to use it, do it with care and remember harm reduction principles.

"Long-term cannabis users showed IQ decline from childhood to midlife (mean=−5.5 IQ points), poorer learning and processing speed relative to their childhood IQ, and informant-reported memory and attention problems.

Source:

https://ajp.psychiatryonline.org/doi/10.1176/appi.ajp.2021.21060664?url_ver=Z39.88-2003&rfr_id=ori:rid:crossref.org&rfr_dat=cr_pub%20%200pubmed

Posted Apr 20, 2022, 6:12 PM UTC

040
psychnerdy•

4:20 blaze it

23
Ecstatic_Purchase_94•

Is the iq decline over that timeframe for non users known ?

14
EntroplessOP•

IQ is a stable trait. Unless people develop dementia or smth.

-28
_Wyse_•

That is false.

And it's spelled "something".

12
freakonature•

Correction, it has a .7 (70%) correlation throughout the lifespan. Not an even 1 (100% correlation). So someone who performed dead in the middle at 100 could score much lower (or much higher) and it would still be considered normal. Source: A study done in Scotland on roughly 300 people age 7 to 70.

4
mrfantastic4ever•

Or watch TV/Netflix all day

-7
edubkendo•

That's a pretty small sample size, tbh.

11
EntroplessOP•

So? if they catch such an effect with small sample size imagine would large one do

-38
Peepsandspoops•

More than likely make the measure of the effect smaller because it's easier to account for outliers and get a better and more realistic measurement of center in larger pools of data (the more your sample represents a population, the less inference you have to make, measurements will be more representative of reality).

Also, using the mean as the measure of center in a small study will highly skew results if any outliers existed in the data, median (and interquartile range) would've been a better measurement to account for outliers as it would inherently be less affected any score outside the fence of 1.5 times the interquartile range, where the middle 50% of the data exists. Median would give us the average score of what was consistent with the bulk of the data.

Mean just takes the entire dataset and finds the center, and doesn't tell if us by itself if any scores existed outside of normal standard deviations from the mean that would throw off results (such as a large drop in IQ from physical or environmental damage, could be lead in the water). Without the data, or a measure like z-scores, this mean by itself doesn't really tell us much where a strong inference can be made. Large outliers can change means wildly, medians are resistant to outliers because they inherently measure more-consistent observations in datasets.

There's a bit of a flawed methodology in statistics at work here. I'd love to see the raw data on the scores, because I have a feeling that a) again, outlier scores are affecting the mean and b) the median drop in IQ can be pretty much accounted for with variance (a 1-3 point reduction seems like it might fall into a margin of error, all things would have to be constant each time they were tested which is impossible in the real world. For example, I sometimes get test anxiety and sometimes don't).

Also, even if the mean was representative of the actual reduction, having the sample group all be from the same basic geographic area is going to muddle what causation inferences you could make if scores were different from non-users and correlated with marijuana causing the reduction - marijuana usage itself might be causing the reduction, or something about how they grow or consume marijuana in New Zealand might be the case (pesticides with heavy metals, poor smoking habits, etc). There could be environmental, physical or cultural factors that could be specific to a geographic area that aren't being taken into a account by the study.

I kind of think there might be a reason the mean was chosen as the measure of center here.. While I'm not going to outright accuse the author of the study of anything without the raw data; keeping a small sample size that's pretty geographically specific, and using the measure of center that skews significantly with the existence if outliers is exactly what one would do if they had a preconceived notion going into the study and were worried that their preconception wouldn't necessarily be represented by the reults. ...or this was just a study with obvious methodological problems that nobody noticed.

20
Daniel01m•

Might make the results less significant due to less extreme results by pure chance.

11
EntroplessOP•

Nope this is not how it works. If effect is indeed big, the less subjects are needed to detect it. If it is small - the more subjects will be needed.

In this case effect is quite large, so less sample is needed. This is the basics of power analysis.

-14
patojosh8•

It's true that if an effect exists, a given participant in a smaller sample size would be just as likely to experience an effect as a given participant in a larger study. However, science does not make assumptions about the results of studies before they are performed. If we were to initially assume that weed makes people dumb before the study, and look for confirmation of that assumption, then a smaller sample size could be more effective. But a larger sample size is better for science because the scientific method involves not making assumptions before performing studies. Daniel is right because more participants mean that more error can be accounted for. Imagine if you flipped a quarter 4 times. It would be pretty likely to get 3 heads and 1 tails. But that's a 75% chance of landing on heads! Imagine if instead, you flipped a coin 100 times. It would be very unlikely that you'd get 75 heads, and much more likely to get a slight deviation like 54 heads or something. 75% vs 54%, those numbers are significantly different but measure the same thing, the chances of getting heads in a coin toss, based on different sample sizes.

9
Daniel01m•

I don’t know tons about stastistics but that seems reasonable too.

But is it not also the case that IF the effect is small it could appear larger due to small sample sizes? I thought that was one of the elementary ”pitfalls” of stastistical reasoning.

1
edubkendo•

A small sample size is less trustworthy than a larger sample, and much more likely to show false correlations. They were also all from the same small city, and born within about one year of each other. That's not a large or diverse enough population segment to make generalizations from, imo.

Meanwhile, other, larger studies have shown less or no evidence of permanent damage to adults who waited to start consuming cannabis until adulthood. See this metastudy for example: https://www.ncbi.nlm.nih.gov/pmc/articles/PMC3931635/

9
agggile•

other, larger studies

Which studies exactly? All of the pooled studies in that meta-analysis are n<100.

1
cenciazealot•

That is such an statistical abhorrence, sample size cannot be translated into a larger difference between two populations.

4
beijumdeoost•

that is not how sample sizes work😂😂

3
Charlielx•

This is the best thing I've read today. So with your logic, we only ever need a sample size of 1, right?

3
[deleted]•

[deleted]

1
youareactuallygod•

Is this comment a joke?

1
[deleted]•

[deleted]

0
s4schwarzz•

Weird - I've been smoking for 8 years now and I'm just getting smarter 🤣

8
Substantial-Ad-3225•

Wow what a truly useless study. This sample from Dunedin has extensive research that shows a much stronger causation for these effects, there’s literally a million and one reason why this correlation, which is rather small, would be attributed to other factors instead of just using cannabis. For example, those who use cannabis in the long term have a high comorbidity for other mental health disorders which can impact IQ and the volume of the hippocampus.

Here is study which assessed the rate at which a diagnosed mental illness before the age of 15 indicated cannabis use within the same same group, keep in mind many mental illnesses are wildly underreported:

Underreporting of mental illness and stigma: https://www.sciencedirect.com/science/article/pii/S0165176517302550?casa_token=MnwMzj32S88AAAAA:4hJw4C4lODIluXuQt5ggr4gt25ujm-2ByclEMRma5AzbxW0_lDGU45R4EXocia3ugOa08t4Bxg

https://dunedinstudy.otago.ac.nz/files/1571962383544.pdf

This study also explores how inappropriate cannabis use can also create mental illness, this point has been debated and a better understanding hints at cannabis potentially exacerbating mental illness when abused by uninformed individuals. Seeing as cannabis is/was illegal this seems like a more likely explanation.

Other studies were able to predict the economic burden caused by childhood risk factors and link them with high risk groups such as obesity, poor brain health, crime and etc. I expect that this study may suffer from a misunderstanding of the societal pathways that may lead to cannabis abuse, and how many people already struggling due to socioeconomic burden, abuse and etc, may cope using cannabis. Although they attempted to control for socioeconomic differences, the manner which this was done is quite poor and under-predicted the effects of socioeconomic differences. In addition they do not account for mental illness as a possible explanation, especially seeing as common disorders such as MDD, ADHD and etc can cause worsening of cognitive deficits throughout a life time.

https://www.sciencedirect.com/science/article/pii/S0010440X19300707

There are plenty more issues with this study, but i believe this is enough so far to make there rather drastic conclusion dubious at best. I am not saying cannabis has no harm, and it can certainly cause problems in specific groups, but the focus should be on addressing the underlying issues and not vilifying a form of self-medication.

https://www.ncbi.nlm.nih.gov/pmc/articles/PMC8834899/

https://www.ncbi.nlm.nih.gov/pmc/articles/PMC5505663/

8
agggile•

there’s literally a million and one reason why this correlation, which is rather small, would be attributed to other factors instead of just using cannabis

You only really bring up one of these factors, without going into much detail. It's true there are other variables, but there is no longitudinal study (or any study at all) which controls for everything. However, this study investigates the effect of long-term cannabis use, not the causation. You need a sufficiently coarse group in order to do so, to establish a trait or a phenomenon, after which you can investigate causation, and finally the effect between a causation and trait/phenomenon.

Other studies were able to predict the economic burden caused by childhood risk factors and link them with high risk groups such as obesity, poor brain health, crime and etc. I expect that this study may suffer from a misunderstanding of the societal pathways that may lead to cannabis abuse, and how many people already struggling due to socioeconomic burden, abuse and etc, may cope using cannabis.

That's not the scope of this study. It is the scope for some other studies, but those studies measure a completely different thing. Are you aware of any longitudinal study that would even attempt to understand every societal pathway to some group inclusion?

Given the million and one other factors impacting cognitive performance, how exactly would you determine the effect of socioeconomic burden or abuse in isolation, free from the concerns you have? The overarching issue is the difficulty of measuring cognitive performance, and that IQ should be completely deprecated from all research - there are a million covariates, and every single one of them suffer from the same issue. It's a limitation in any cohort involving humans.

Although they attempted to control for socioeconomic differences, the manner which this was done is quite poor and under-predicted the effects of socioeconomic differences.

That's pretty vague. Do you mean they under-predicted the effect of socioeconomic status in the context of study results, or its causation to long-term cannabis use? Childhood socioeconomic status is controlled for, and while there are differences in "transient" socioeconomic status, the effect should be fairly minimal across multiple cohorts in a longitudinal fashion.

In addition they do not account for mental illness as a possible explanation, especially seeing as common disorders such as MDD, ADHD and etc can cause worsening of cognitive deficits throughout a life time.

It would be nice to have results by DSM criteria per cohort. However, MDD does not appear to have a significant effect on IQ, though results are more drastic with a comorbid psychiatric illness. What do you make of the long-term alcohol cohort that did not show such an effect (table 2)?

There are plenty more issues with this study, but i believe this is enough so far to make there rather drastic conclusion dubious at best.

The conclusion is that if you take a group of people that have used cannabis for a long time, there is a statistically significant difference in IQ scores if you compare this group to other groups of people. This isn't equal to "cannabis use reduces IQ".

I'd be curious to hear about these other issues. So far the criticism is not really related to what this study is attempting to do.

0
Substantial-Ad-3225•

thanks for the thoughtful response, your definitely right in that I misplaced my annoyance. Had just walked out of an exam lmao. The OP moreso set me off.

I guess my problem is more how these type of studies are used to draw conclusions that are outside of the scope of the study, like the OP FE. Nothing about the study said that people were getting dumber from weed, instead it says that some people who use weed might have decreasing IQ throughout the years, and the reason why is not established, but I do think that these types of studies end up doing more harm than good. Cause at the end of the day what is this study going to be used for? Policy decisions, stigmatization and etc, it doesn’t really explore what could be causing this and provides no direction or insight on how to help people and doesn’t outline or explain future studies that could explore this relationship. I understand that might be outside of the scope of the study and some data could be published purely to be published, but that becomes an enormous issue when you take into account the file drawer problem, many studies that might contradict this paper would have a low likelihood of getting published, or any study that failed to meet there hypothesis would as well. This means that what ends up getting published has a greater outcome on public policy/opinion and stigmatization, like I’m sure I will see tucker Carlson or someone similar raving about this study in the coming weeks.

And yes you are definitely right in that IQ is an incredibly flawed and stupid way to measure intelligence.

I meant more so in its potential causation of cannabis use. Like differences in stressors that might lead someone to start using cannabis as a coping mechanism.

Sorry poor wording on my part, I meant untreated mental illness can cause cognitive deficits throughout a life time, which is what the paper explains.

Also I’m curious what you think the study is trying to do? Like why did they conduct this study? Are they trying to benefit someone?

1
agggile•

I don't think it's wrong to study something like this, and that it's in fact instrumental for studies like this to exist for any future clarity. But that being said, all science gets misquoted and misrepresented for various agendas, I'm sure some media took this study and ran it with a headline among the lines of "cannabis lowers intelligence". It's frustrating, but as a practice I don't find it exclusive to anti-drug agenda or anything, just that the people/journalists writing about science are not always very science-literate.

Public opinion might be affected but I'm confident it has little effect on actual developments involving drug prohibition or policy in general (at least it shouldn't, not sure about America however). If anything, this study shows that the effect is quite small and potentially explained by a factor involving cohort inclusion.

There are equally frustrating takes involving scientific studies from drug users or pro-drug people - like digging up some in vitro study, a personal anecdote and calling it evidence. For some reason it's generally celebrated in reddit and elsewhere, when it's exactly the same thing various prohibition/policy proponents abuse with studies like this. Maybe some sort of tribalism.

2
adabbadon•

I can't help but wonder if there's a greater connection between the reasons that people use cannabis long term and who also have other behavioral patterns that lead to lowered IQ. I began self medicating PTSD with cannabis and later on was diagnosed with ADHD and realized that I was using it to cope with that as well. People with mental illness and learning/attention disorders may struggle more with self care and face greater barriers to pursuing intellectually stimulating tasks, leading to lowered intellectual capability compared to their peers. There are other potentially confounding factors as well. I'm not going to argue that weed is harmless but it also isn't harmless to prop studies like this up as if they are undeniable proof that cannabis use is harmful.

7
jubululu•

I hate how you say Cannabis will make you stupid bro it doesn’t make you stupid it makes you okay with not learning new skills or working on skills that you need. It depends on the person. There are millionaires that smoke. I would say the IQ decline is due to inactive training of focus and thought processes

6
coolbird42•

Tsss buzzkill

2
lonewolf1418•

right, terrible long-term sides imo

2
Sitting_Under_Trees•

That’s probably true. But I’m still rocking a 132, so I guess I had a few extra intelligences to spare.

2†
HonorTime•

What does it change having 5 less iq points? Genuinly curious, if anybody knows please let me know

2
adabbadon•

IQ has a mean of 100 and a standard deviation of 15, meaning that 2/3 of people have a score between 85 and 115. So a loss of 5.5 points won't take someone from genius to intellectually impaired, and it is unlikely to cause much noticeable impact to the person.

IQ is a really flawed conception of human intelligence for a lot of reasons. But more than that, the emphasis that we place on it is flawed. Intelligence changes throughout life as our cognitive abilities change, as we grow (or languish). A small loss in intellectual ability is not the end of the world. Intelligence alone does not determine someone's happiness or success in life.

I think this quote (from Wikipedia) does a better job at explaining my incoherent thoughts than I can right now:

While IQ tests are generally considered to measure some forms of intelligence, they may fail to serve as an accurate measure of broader definitions of human intelligence inclusive of creativity and social intelligence. For this reason, psychologist Wayne Weiten argues that their construct validity must be carefully qualified, and not be overstated. According to Weiten, "IQ tests are valid measures of the kind of intelligence necessary to do well in academic work. But if the purpose is to assess intelligence in a broader sense, the validity of IQ tests is questionable."

...Along these same lines, critics such as Keith Stanovich do not dispute the capacity of IQ test scores to predict some kinds of achievement, but argue that basing a concept of intelligence on IQ test scores alone neglects other important aspects of mental ability.

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[deleted]•

[deleted]

2
HonorTime•

Thank you. That makes sense I never understood why someone with high iq should be considered smarter whatever It means. If I'm not wrong iq tests gotta be completed in a short amount of time and are mostly deductive things. So a person that needs his time to think or someone with ADHD should be as smart as kangaroos? Then there's the fact that scientists came to the conclusion that there are a lot of types of intelligence and I think iq regards one maybe two of em.

1
adabbadon•

Yeah a lot professionals are starting to prefer multimodal theories of intelligence, that encompass a broader range of abilities. Intelligence as we currently measure it tends to be biased towards those who have the wealth and privilege to be educated. It's frustrating that inequity (at best, and eugenics at worst) has historically been perpetuated because of IQ tests.

1
poopdirt1•

Ill just get more stupid

2
LabeVagoda•

Just get so stupid you can't read a cannabis study and you're all good

2
DangAsFuck•

I'll take "studies designed to prove the hypothesis correct" for 500, Alex.

2
[deleted]•

Thanks tips. No one ever said we should be smoking cannabis in our youth. That has a total lack of respect for harm reduction. What are the results when it’s long term but only starting as an adult? I think this was posted because someone is butthurt over cannabis.

2
infrareddit-1•

What is the harm reduction strategy here?

1