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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: 1, Interesting) by Anonymous Coward on Wednesday January 20 2016, @01:47AM
I started taking Fluoxetine (Prozac) about three months ago -- I guess I'm lucky because it really works for me. I wish I had tried it 15 years ago. I was worried it would make me stupid, but the opposite is really the case. I used to work on hard projects as a way to distract myself from my self-dialog/excessive negative thoughts/anxiety. Now I work on the same projects for fun. It's a difference that makes life seem worthwhile rather than a chore.
I know they don't work for everybody, and I'm empathetic toward you because they don't work for you, but for anyone who has been living with a constant barrage depression and internal negativity, it's worth a try. I was at the point where I really felt like I just wanted to die and figured I should at least try medications before buying a tank of nitrogen gas. Now I wish I would have tried prozac years and years ago, but, at the same time: "whatever". One thing about prozac, it has helped me build up what I consider a healthy sense of apathy -- if you care too much about everything you do always being perfect, and beat yourself to a pulp for the slightest failures, life is a horrible torture. It takes a little apathy to make life good -- some people will understand that.
(Score: 3, Insightful) by kurenai.tsubasa on Wednesday January 20 2016, @03:27AM
My roommate has actually had great success with Zoloft after being burned by Prozac. I think each individual needs a tailored healthcare solution when it comes to depression.
Many of us are depressed for vastly different reasons, and that would I think at least imply different cures. I'm happy for you! Huge success!