I don't want my teens to use weed until they're older, and I never tried it until I was an adult. I agree with your ideas, but I also wonder how much you can rely on this kind of data about a substance that is/was illegal and/or not socially acceptable, because of what kind of people are willing to take the risk.

Knowing now that many people use cannabis as "medicine" to treat things like depression, anxiety, ADHD, autism spectrum, ... I wonder how many "recreational users" are self medicating to some degree. Even those conditions carry social stigma and often aren't treated professionally.

So when a kid with an untreated underlying condition, even a minor one, tries weed and experiences some amount of relief, in addition to whatever "fun" it is, they're more likely to use it again vs someone for whom it is merely enjoyable.

And those conditions, when untreated, or not successfully treated, are more likely to lead to a less "positive outcomes" than someone more neurotypical. They are more likely to have trouble with school/work/relationships. I say this as someone dealing with depression and ADHD for a long time.

In addition, for people who enjoy the use of this substance, even for purely recreational purposes, are more likely to use it unashamedly if they have a more antisocial personality to begin with. That's obviously not to say that only people who are antisocial like weed or other drugs. But that, they are less likely to be ashamed or worried about being judged by friends and family for using it, and more likely to take the risk of getting caught by authorities.

I think these things apply because these studies aren't looking at individual case studies to find a direct casual relationship, but are talking about statistics and using the correlation of a group of people on the margins, being X% more likely to show certain behaviors. They're trying to say, compare this group of people who used weed, vs those who didn't, and see if there's a higher chance of future problems. Unfortunately, with self selecting groups, you don't know what "problems" they had in the first place.