Largest twin study of adolescent cannabis use finds no relationship between heavy use & IQ decline

Largest ever longitudinal twin study of adolescent cannabis use finds no relationship between heavy use and IQ decline

A new study led by scientists from UCLA and the University of Minnesota attempts to examine the link between marijuana use and IQ in a larger context. Reporting in PNAS, the authors analyze results from two longitudinal studies of twins, with data from more than three thousand individuals from Southern California and Minnesota. Participants were tested in six cognitive areas at two time points: between 9-12 years of age, with follow-up between ages 17-20. Study subjects self-reported marijuana use and frequency, and additional information, including genetic data, family background, socioeconomic status and use of other substances was collected at each encounter.

The authors focused on three criteria they proposed as measures for evidence of a direct causal relationship between marijuana use and cognitive decline. First, if marijuana use causes IQ decline, as opposed to merely being associated, then poor cognition scores should only be evident after use begins, and not before. Second, with a causal link, a dose-response relationship – that is, higher decline with heavier marijuana use – would be expected. And finally, if the relationship is causal, then the association of marijuana use and IQ decline should remain, even after genetic and social factors are taken into consideration.

One of the biggest arguments against legalization of marijuana is that it makes you dumb, especially the kids, and is therefore dangerous. Think of the kids! Problem is, that argument was made based on no evidence, just stereotyping. From these arguments will eventually come a fact finding mission and today we learn that smoking, eating, or vaping the pot does not make you stupid. The facts are in because they are based on science but I doubt that will stop anyone opposed to marijuana, like politicians and law enforcement.

The DEA will continue to keep marijuana listed as a schedule 1 narc, higher than coke, and declare it has no medical value yet DC has legal medical marijuana.

a reply to: Swills

That's absolutely fantastic news!

The one and only thing that 'bothered' me about marijuana was believing that it had some kind of minor damaging affect to young minds (at a biological level).

Thanks for the news

a reply to: Ghost147

Perfect! Than you are the person I wanted to reach about this issue!

a reply to: Swills

Haha, well, I wasn't against marijuana at all to begin with. It's just that particular detail was unfortunate. Now, though, when my wife and I have kids, they'll be puffin' the reefer out of the crib!



Maybe not that young...

And not that forced....

a reply to: Swills

i bet if they did the same test with floride they would find why kids are getting stupider

a reply to: Ghost147

Against it or not, this is news for everyone who thinks pot makes you dumb over time. Marijuana gets a bad rap so it's great to see the tides turning with legalization and science.

Legalize pot already. This is stupid.

a reply to: DOCHOLIDAZE1

This studies exist and are used all the time in the fluoride debates.

a reply to: Swills

There are twin studies with flouride?
Off topic but I would be interested in seeing them. I've been involved in many such discussions.

a reply to: Ghost147
You may be interested in this result:

Among the six IQ-related areas tested, the authors found decreases in ability among marijuana users compared to non-users in two modules – Vocabulary and Information – associated with “crystallized intelligence”, or the ability to use learned knowledge.

news.meta.com...

a reply to: Phage

Twin studies? That I don't know off the top of my head. If you're interested search for Chinese fluoride studies.

a reply to: Phage

But there was also this,

Finally, the authors examined the effects of outside factors associated with IQ decline. They found the decrease in Vocabulary scores was reduced in one study and “completely eliminated” in the other when adjusted for participants who self-reported binge drinking and use of other drugs. The authors also focused on twins where one sibling used marijuana and the other didn’t, assuming similar genetic, socioeconomic and environmental factors for each member of the pair. These analyses, performed on more than 200 twin pairs, found no significant difference between users and non-users.

originally posted by: Phage
a reply to: Ghost147
You may be interested in this result:

Among the six IQ-related areas tested, the authors found decreases in ability among marijuana users compared to non-users in two modules – Vocabulary and Information – associated with “crystallized intelligence”, or the ability to use learned knowledge.

news.meta.com...

But they do go on to say this :

The authors noted, however, that in one of the two studies, the baseline IQ scores of eventual users were already significantly lower in the affected areas. Here, marijuana use does not precede cognitive decline, and they point out prior evidence that suggests other factors such as behavioral disinhibition and conduct disorder that may predispose individuals to both lower IQ and substance use.

So it is possible said inviduals would have a similar result regardless of marijuana use...

a reply to: Swills
I am aware of the Chinese studies, as well as their flaws.
Since the topic is about a twin study, it seemed by your statement that there are twin studies involving flouride.

This studies exist and are used all the time in the fluoride debates.

Apparently I misunderstood. As I said, off topic anyway.

a reply to: Phage

Yeah, I was thinking he was talking about studies in general, not just involving twins.

a reply to: Swills

I'd like to see the study instead of a second hand account.

Mind you, I'm pretty much in the same camp as the rest of you on this but the effects of pot on developing brains is obviously a topic of concern.

a reply to: Phage

You'd like to see the study itself instead of relying on the article? If so, it hasn't been released yet.

a reply to: Swills

Yes. I know that.
I checked, I always do.

a reply to: Swills

I tryed to access it too, but it seem's like the blogger linked an undiffused early version.

a reply to: PersonneX

No author names. No title.
Claims it's been published in PNAS. But nothing relevant shows up there.
Frustrating.

a reply to: Swills

I hope that when the study is released it will show exactly what this thread says.

I always found a quiet whatever helped settle me down for studying - but that's another matter so I am glad to read this thread.

I doubt few today believe the 'official line about cannabis because we all know the benefactors of getting rid of that plant and we are facing the problems such as pollution from insecticides because of it along not to mention people's lives ruined because they fancied 'forbidden fruit' etc.