The Causal Effect of Cannabis on Cognition

Does smoking lots of pot make you dumb or do dumb people smoke lots of pot? Mostly, the latter. Ross et al. (2019) write:

Although many researchers have concluded that cannabis causes impairment in cognition, there are alternative explanations. First, poor cognitive functioning is a risk factor for substance use. Specifically, EF measured in childhood predicts later substance use and substance use disorders (SUDs; Ridenour et al., 2009). Thus, studies need to control for prior cognitive functioning (Meier et al., 2012). Second, poor cognitive functioning and cannabis use may also be related, not because one causes the other, but because they share common risk factors, like lower SES (Rogeberg, 2013). Lynskey and Hall (2000) proposed that early use is likely to occur in a social context characterized by affiliations with substance using peers, poor school attendance, and precocious adoption of adult roles including dropping out of school; such an effect on educational participation may also influence later cognitive functioning.

Indeed–twin studies which control for genetics and family environment–do not find that cannabis reduces cognition:

Lyons et al. (2004) examined MZ twins discordant for use 20 years after regular use, and found a significant difference between twins on only one of 50+ measures of cognition. Second, Jackson et al. (2014) found no evidence for a dose-dependent relationship or significant differences in cognition among MZ twins discordant for cannabis use. Similarly, Meier et al. (2017) found no evidence for differences in cognition among a combined sample of MZ and DZ twins discordant for cannabis dependence or use frequency. Thus, quasi-experimental, co-twin control designs have yielded little evidence that cannabis causes poorer cognition.

Ross et al. run a similar study but testing also for executive function skills–the ability to plan, focus, control impulses and so forth which are skills related to IQ but distinct–and they conclude:

Families with greater cannabis use showed poorer general cognitive ability. Yet within families, twins with higher use rarely had lower cognitive scores. Overall, there was little evidence for causal effect of cannabis on cognition.

Hat tip: The excellent Kevin Lewis.

 

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Has any social scientist ever proposed that the government should forcibly separate a certain percentage of identical twins born each year, to further research?

I seem to recall that the Nazis did. And that subsequent researchers still read the results under their bed covers with a flashlight.

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Only in this way we can transform medicine into a science.

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Check out the movie "Three Identical Strangers" for something really on target about this.

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I don’t think smoking dope necessarily makes a person dumber. I believe the real issue is more insidious, which is that it makes the mundane more tolerable.

I think people who would otherwise make more of themselves because they’re bored or stuck in a rut find dope makes their present situation “acceptable”.

This is consistent with my own observations but it would be interesting to see if this could be tested in some way.

Dope is the opium of the people.

Why do people call it "dope?"

Theory # 1. They call it dope because that's what it is.
Theory # 2. They call it dope because it turns users into dopes (theory apparently disconfirmed).
Theory # 3. They call it dope because dopes use it (apparently supported)
Theory # 4. Dope (weed) and Dope (ignorant person) are etymologically related but semantically unrelated homonyms (Dope from Dutch word doop, meaning sauce. Dupe however comes from a difference word source). This is speculation on my side. cannabis scholars would have a better clue, to be sure. Interestingly, most of my associates at one time were drug users and I never heard any them refer to Mary Jane as dope).
Theory # 5. None or all of the above.

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I think it really depends on the person and the situation. Most of the people you see smoking weed don't care about their image. You would be surprised by the number of highly successful people that smoke weed because they are smart enough to avoid its stigma by consuming privately.

Exactly. Just another MR paper link that starts with a pop culture caricature premise, and promptly stumbles over correlation/causation.

There are people who have an addictive personality. They must consume alcohol or dope. They enjoy losing large portions of their life. They are willing to sacrifice their marriage, their children and their job for that high/low that they need and cannot abstain from. You can never trust them, you shouldn't employ them and you should not form any kind of a relationship with them. They are not normal and will never be normal.

They are not willing to lose, that's why it's a dammed addiction ;)

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Most highly successful people that smoke weed don't smoke it every day. That's one reason they're highly successful.

It would be interesting to know what counts as "cognitive function," and under what conditions our favorite stoners were tested - before or after smoking? One thing I've noticed for sure among frequent smokers: their biggest problem is their inability to control their emotions and reactions when NOT stoned. Stay clear of the forklift driver left wanting this morning for a bong hit.

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It’s nice to see that Mr Lewis has regained his excellent status.

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"The excellent Kevin Lewis."

Sp Kev is promoted back to being "excellent" again. What explains his brief demotion? Or was it Mr Cowen to whom the question should be directed?

He crossed Dr Cowen.

Won't happen again.

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"Correlation need not imply causation" is a pons asinorum for a large chunk of the population, including a large chunk of those who consider themselves educated. I imagine that this case will be waved aside by such chumps.

(I read a piece recently by a medical man, a physician whose writings had persuaded me that he was an intelligent, sceptical, reflective sort of a bloke. And then he argued that such-and-such a correlation coefficient was so high that it must surely imply causation. The forces of reason are doomed to defeat.)

You know, i dunno if poverty causes crime, or crime causes poverty, but I lock my car doors in poor neighborhoods either way.

But we know that crime causes locked doors.

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Does drinking lots of alcohol make you dumb or do dumb people drink lots of alcohol ?

It makes you American.

No it makes you British. They need the alcohol to dull their dental pain.

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Nice try, Alex, but I doubt whether cannabis consumption can explain the poor performance of late by our esteemed Cognitive Elites.

(Maybe some metrics are available that could tell us how Cognitive Elite performance could be enhanced by regular cannabis consumption.)

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It's the same as tattoos - they don't make you dumb, but they are a good signal.

Ok boomer

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Good points. We, Americans, got sadly used to see our leaders (Biden, Clintons, Trump, etc.) using their power to line thier pockets and blocking investigations on their miseeds. Meanwhile, Brazil's leader, President Captain Bolsonaro, when told his party's president, Mr. Bivar, may have benn involved in corrupt dealings, immediately ordered a federal investigation and fired Mr. Bivar's right-hand man, Mr. Waldir, from the party leader at Congress position. Maybe we should follow Brazil's example. Certainly, simple honesty is not too much to demand of men in government. We find it in most. Brazilians demand it from everyone.

Maybe watching the elite avoid all serious investigation regarding their exploitation of citizens like Jeffrey Epstein’s relationship to all the above mentioned let alone Alex’s favorite economist Larry Summers leads populace to say WTF, might as well get stoned.

So that is. A desperate America will be swept by cold, harsh winds of nihilism. It is sad.

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A similar study was done on followers of Trump to determine whether Trump caused them to be stupid or they arrived stupid. It turns out they arrived stupid.

Is there a class of drugs where it's the non user that has the greatest reaction?

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Paper is gated so I can't read it but previous studies I've seen considered fairly low usage as "regular". I'd be interested in seeing if there's an effect for those that smoke daily. (Based on anecdotal evidence that is the level at which it seems to impair cognition more).

Based on my personal observations, the dividing line can start with those who spark up in the morning on weekdays.

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I’m a terrible sleeper, and have been all my life. Ongoing lack of sleep has been a consistent problem for me and certainly reduced my cognitive function at times.

My physician prescribed a cannabis tincture that I take every night before bed, and my sleep has improved quite a bit. In my case, I would suggest that cannabis has made me smarter.

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All very interesting, but let's not forget that smoking dope is fun, and so is drinking alcohol. Let's have research papers about that!

I see and fear the puritan streak in Americans, surfacing here as extreme risk aversion, with all worried to death that someone, somewhere might be having fun.

The narrative about America's supposed anti-fun Puritan streak has been obsolete since at least the 1960s.

Yeah, for 21 year olds! :-)

Compare to civilized countries.

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This just makes it more curious to me what the brain changes in marijuana users actually manifests as.

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Are there twin studies on the munchies?

OMG!!! The munchies!! That is SO funny!!!!

A quiet chuckle will suffice

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Sometimes you just want to get lifted with the boys and listen to some tunes, maybe have a cook up. Watch a comedy and have some laughs.

Life doesn't have to always be all about optimising your academic/financial/career/familial legacy.

Plus sex on a little bit of weed is amazing. Not so much you get lazy, but it completely blows sex on alcohol out of the water.

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>Does smoking pot make you dumb or do dumb people just want to smoke pot?

Rest easy, little Al — everyone here knows you would never cite a study supporting the former.

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The most significant gene for cannabis taker is CADM2, crosstabulation with other phenotypes from UK Biobank data, in particular nervous risk taker who fathered lots of children (sample gender biased?) and with family relation issues, sample size 147,555

Phenotype | Top variant | Top p-value
Ever taken cannabis | rs113642272 | 2.0e-16
Nervous feelings | rs1449386 | 2.4e-19
Suffer from 'nerves' | rs72585634, rs35875166 | 2.2e-15
Risk taking | rs62250712 | 1.3e-30
Drive faster than motorway speed limit | rs112438529 | 4.4e-20
Number of children fathered | rs75964821 | 4.4e-15
How are people in household related to participant: Son and/or daughter (include step-children) | rs2647714 | 5.5e-8
Types of physical activity in last 4 weeks: Other exercises (eg: swimming, cycling, keep fit, bowling) | rs1691471 | 7.1e-16
Types of physical activity in last 4 weeks: Strenuous sports | rs74343554, rs398062542 | 2.5e-12
Leisure/social activities: Sports club or gym | rs74343554, rs398062542 | 7.2e-10
Workplace had a lot of diesel exhaust: PHESANT recoding | rs9876664 | 7.0e-8
Mean ISOVF in retrolenticular part of internal capsule on FA skeleton (right) | rs2326267 | 8.5e-8
Home area population density - urban or rural: England/Wales - Hamlet and Isolated Dwelling - less sparse | rs79906023 | 1.7e-7

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highly dubious stuff. cannabis is a psychotropic drug. that means it affects cognition by definition.

you can game the definition of "dumb" various ways (by playing with the dosage, focusing on super long term effects, etc). but everyone I've known who uses marijuana on a regular basis assumes that a certain amount of mental fog is the price of admission.

my guess is that Alex finds this study credible because he has never smoked pot

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Maybe marijuana should be legalized, but employers should be allowed to screen out marijuana users as an IQ filter.

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