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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 Gravis on Thursday January 21 2016, @09:44PM
To me, you're no better than those who say we should have mass surveillance to stop the terrorists
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you will abandon everyone's freedoms when you want to increase safety.
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Well, maybe not you, since you seem to think living in padded rooms is okay.
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But your thought process appears to be so authoritarian in nature that it seems likely that you would find any given reason to ban something that you don't like to be good enough, so I'm wasting my time.
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I'd rather just pay more taxes than live in the tyrannical society you seem to desire.
"Splitting (also called black and white thinking or all-or-nothing thinking) is the failure in a person's thinking to bring together both positive and negative qualities of the self and others into a cohesive, realistic whole. It is a common defense mechanism used by many people.[1] The individual tends to think in extremes (i.e., an individual's actions and motivations are all good or all bad with no middle ground)."
you are your own problem, not me.
(Score: 2) by Anal Pumpernickel on Friday January 22 2016, @12:05AM
Nice try, but that has nothing to do with the validity of what I said.
(Score: 2) by Gravis on Friday January 22 2016, @08:38AM
to be clear, i'm not participating in a flame war, so i'm done discussing the matter with you.