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Meta at Science News reports on a new study (DOI: 10.1073/pnas.1516648113) still paywalled at PNAS:
Marijuana is used more than any other recreational drug, with recent trends toward greater social and legal acceptance in some regions. Concerns remain, however, about a possible causal relationship suggested in scientific studies between marijuana use and decline in IQ.
A new study from two longitudinal studies of twins, examine the link between marijuana use and IQ using data from more than three thousand individuals from Southern California and Minnesota.
The study by scientists from UCLA and the University of Minnesota focused on three criteria they proposed as measures for evidence of a direct causal relationship between marijuana use and cognitive decline.
- 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.
- If a causal link exists, a dose-response relationship would be expected.– that is, higher decline with heavier marijuana use.
- finally, if the relationship is causal, then the association of marijuana use and IQ decline should remain, even after accounting for genetic and social factors.
In tests of abstract reasoning and problem solving associated (called "fluid intelligence") showed no significant differences between uses and non users.
[more]
The study did find decreases in ability among marijuana users compared to non-users in the ability to use previously learned knowledge. (Vocabulary and Information retrieval, or so called "crystallized intelligence".)
The authors noted, however, that 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 criteria 1 above was not met).
The study also found no relationship between heavier or more frequent marijuana use and the magnitude of IQ decline.
(Criteria 2 was not met).
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.
(Criteria 3 also failed).
The authors conclude that taken together, the results provide "little evidence to suggest that adolescent marijuana use has any direct effect on intellectual decline".
(Score: 2) by Phoenix666 on Wednesday January 20 2016, @11:16AM
My brother-in-law is a long-term, heavy user. I've watched him for 20 years, and I can't say his cognition has changed much; he can reason and remember as well as he ever could. Something has changed in his brain. With his usual dose he's the sweetest, most easy going person, but if he goes more than a day without a hit he turns into the world's biggest asshole. Also, he's totally unable to cope with any interruptions to his routine. The unexpected brings him high levels of anxiety. I don't know if other heavy users experience this, if it's a by-product of its being illegal and requiring elaborate measures to avoid detection, or what, but it has been sad to watch such a naturally gregarious person transform into a virtual recluse because he can't deal with the unpredictability of others.
Sample size of one and all that, but the effects we've observed make us want to keep our kids away from it.
Washington DC delenda est.
(Score: 1, Interesting) by Anonymous Coward on Wednesday January 20 2016, @02:46PM
I know of at least 3 other people who are the same way.
I not sure it is a chemical dependency but it most certainly is a mental one.
They do not have the emotional fortitude to 'deal with it'. Their way to 'deal with it' is to get fucked up so they dont care. When they are not baked they realize 'oh wait I DO care and everything is fucked up' so they turn grumpy. Then they bake off another one 'to deal with it'.
My wife who has not touched it in 10 years is paranoid as ever (fun game for me is "Hey look a cop"). Like your brother-in-law is unable to cope in any way with any change in routine. I mean the smallest thing messes her up. Like "hey lets go out to eat instead of eating in tonight" she flips out. Then she realizes she is being irrational and apologizes.
(Score: 0) by Anonymous Coward on Wednesday January 20 2016, @03:42PM
It would not surprise me at all if what you're observing is that cannabis is an effective treatment for what many would call his nature mental state.