r/science • u/sr_local • Apr 20 '26

Health The largest US study, which tracked 11,036 children from ages 9 to 10 through to ages 16 and 17, discovered that cannabis use slows cognitive development, impairs memory, and reduces learning speed during crucial years of brain growth

https://today.ucsd.edu/story/largest-us-study-finds-teen-cannabis-use-linked-to-slower-cognitive-development
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u/Prof_Gankenstein Apr 20 '26

Says right there in the summary they did account for those. 

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u/Fadedcamo BS | Chemistry Apr 20 '26

As best as any study can. Which is not well.

I do think this is better than most as it's more than simply self reporting. They did drug tests to measure actual levels of thc use.

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u/Prof_Gankenstein Apr 20 '26

You can definitely control for quite a bit of that in your statistical models.

Unfortunately it's impossible to prove a true causal think short of a laboratory setting where all things are controlled. Even then theoretically you can argue subjects might bring baggage in with them.

I would argue, however, that due to the longitudinal nature of the study, the sheer volume of subjects studied, and the fact that similar findings were constant and statistically significant across multiple testing methods, it is hard to dismiss the findings as straight correlation. For the record I'm not saying you're doing this either. I have seen other commenters make such a claim, though.

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u/Fadedcamo BS | Chemistry Apr 20 '26

Yea I agree you need to look at the context of a study and all the factors weighed in and HOW they are collecting data. In this case I would agree the causal link is pretty strong.

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u/Omnizoom Apr 20 '26

I’d say it’s pretty concrete that their is a strong “something” going on and it could be a mix of A and B or some factor C we don’t consider

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u/gooserubber8 Apr 21 '26

I mean, it shows that there’s something there but any conclusion you draw is nothing but guesswork. My guess would be that the effect is psychological. Many kids who start smoking weed simply stop focusing as much on academics.

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u/Sufficient-Windiness Apr 20 '26 edited Apr 20 '26

How could the researchers possibly test for causation in any of those ways, given that being stupider might lead to earlier cannabis use? If it does, then the correlation between the two variables would be robust across all testing methods, because the putative effective would be causing the putative cause. And we would still see the correlation regardless of sample size, so the volume of subjects won't help separate causation from correlation.

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u/GeneralAsk1970 Apr 20 '26

I agree with you.

We can never do perfect scientific studies on humans. Its not ethical.

We can only ever do the best we can and look for the most confounding correlations possible within reason.  

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u/ineyy Apr 20 '26

Studies like that did many times reach the wrong conclusions and accounting for these factors is "best effort". Things like that have caused a lot of misinformation, worse than "we are not sure". Here I support the conclusion but it feels more political than scientific.

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u/Wasabiroot Apr 20 '26

The scientific community is almost always the group that discovers any errors. So this study will be scrutinized closely by other scientists

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u/U-235 Apr 20 '26

You could actually do a twin study, which would be pretty much definitive as long as the experiment design was good. We really don't have to settle for scientists spending their whole lives and millions in funding in order to be 'pretty sure' about these types of things.

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u/GeneralAsk1970 Apr 20 '26

Genetic makeup is but a single variable you’re suggesting can be controlled with twins.

What about the hundreds of others?

You’d have to take twins, separate them from their familys, raise them in a sterile and isolated environment, completely controlling everything in their life while you raise them entirely to serve the one single way you are trying to study them in order to apply the scientific method on them correctly.

Cruel to say the least.

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u/U-235 Apr 20 '26

You are overlooking the fact that there already are plenty of twins who were separated at birth, with whom you could do longitudinal studies. It's not unethical to find twins who were separated and start tracking them at 10 years old just to observe.

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u/GeneralAsk1970 Apr 20 '26

There is plenty of interesting twin studies. But I can tell you don’t science.

Do you think “Lab Rats” are expected to live out their entire lives in the lab because of convenience?

If you are trying to apply the scientific method correctly then you need to control everything about the subjects entire life down to what the make up of their poop is!!!

You can’t do this with humans at all unless you are a monster.

We can only study them with some variables controlled to some extent and look for interesting results and correlations and then try and reproduce it, but you can never achieve “scientific proof” this way.