I just want to throw my two cents up here about the whole study thing since it looks like its getting some people down.

My main issue with the study here is their methods. For this study, they gathered a bunch of people who were born in the same range of years and took neuropsychological surveys/studies at certain age points in their lives while also accounting for cannabis use at the time of the exam. Here, those ages were as follows: 18, 21, 26, 32, and 38 (They took more exams before and after these dates but this data was not included in this study). This is where the first issue is for me. They state that

At each of the five study waves between ages 18–38 y, study members self-reported the total number of days (0–365) they used cannabis over the preceding year

While it may be a nitpicky thing, to me it seems that this study is lacking a consistent body of "adolescents" from which they can collect data. They are only taking points from age 18 and later and they way they collected data from cannabis use would only account for age 17 as they only asked about the preceding year. While this may not be a big deal in the application of things, what they are observing may still be happening, it is a big deal when you think of the claim they are trying to make. The paper is titled "Persistent cannabis users show neuropsychological decline from childhood to midlife". Saying "childhood" or even "adolescent" is kind of hard when you only have self-reported data, which can be pretty inaccurate, from ages well into late adolescence.

To be clear, what they are saying may still be happening; there may still be a big impact that weed can have on people's minds at early ages. Just for me the dots between age studied, age claimed, and effect claimed are just too hard to connect with the data they present.

So maybe you don't have to feel quite as bad about teenage use? Honestly what I read doesn't really change anything or blow me out of the water like I expected based on the post and the Forbes article. And for the record I am by no means an authority on this matter. I'm a lowly BS in Bio, if someone better suited or with fancier titles wants to step in or just throw my thoughts out the window feel free to do so!