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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: 4, Funny) by snufu on Wednesday January 20 2016, @01:56AM
You're a towel.
(Score: 2) by Subsentient on Wednesday January 20 2016, @05:37AM
The only other fan of towelie spam in weed articles I've ever met. Keep up the good work, and don't forget to bring a towel!
"It is no measure of health to be well adjusted to a profoundly sick society." -Jiddu Krishnamurti
(Score: 0) by Anonymous Coward on Wednesday January 20 2016, @02:59PM
Proper towel use: it's important!
(Score: 2) by mcgrew on Wednesday January 20 2016, @06:58PM
I see this kind of reference that I have no clue about rated +4 funny and think, damn, I'm getting old. Someone clue me in?
Carbon, The only element in the known universe to ever gain sentience
(Score: 2) by Joe Desertrat on Wednesday January 20 2016, @07:17PM
Do a quick search for "south park towelie" and you'll have all the answers you could ever want. Don't forget to bring a towel!
(Score: 2) by mcgrew on Wednesday January 20 2016, @08:49PM
Hmmm... I have a LOT of South Park on DVD, but I haven't watched it in years.
Carbon, The only element in the known universe to ever gain sentience