Further, cessation of cannabis use did not fully restore neuropsychological functioning *among adolescent-onset cannabis users*.
They did not find a 6-8 point decline for folks who gave up cannabis if they started later in life. In fact they found no decline in IQ whatsoever for folks who started later in life - both when using it and after stopping.
In contrast, within-person IQ decline was not apparent among adult-onset persistent cannabis users who used cannabis infrequently (median use = 6 d) or frequently (median use = 365 d) in the year before testing.
> There's a lot less known about cannabis at this point, but what we know so far isn't very positive.
... for adolescents. Both your studies only show impact in youth.
I don't think my summary was unfair. I was only asked if there was evidence for persistent effects. There clearly is, even if just for adolescents.
It's also important to point out that for the adult-onset group they only looked at 1 year back. This doesn't preclude the possibility that longer periods as an adult find different results.
Your summary missed a critical piece, which is that it is just for adolescents.
I don't think, even within the marijuana community, that there is any debate that marijuana use in adolescents is harmful. I regularly see /r/trees comments telling teens to stop until they're at least 18 and their brain finishes developing.
Sorry, I took a look at the study and I couldn't tell - what is an adolescent? Like, 10-18? 14-25? I know what the word means, but for a scientific study I assume there's a specific range they're referring to.
A New Zealand study found that persistent cannabis users had a 6-8 point decline, even if they had given up cannabis: https://www.pnas.org/doi/abs/10.1073/pnas.1206820109
Here's a meta review that found a 2 IQ point drop across a wider range of usage types: https://www.cambridge.org/core/journals/psychological-medici...
There's a lot less known about cannabis at this point, but what we know so far isn't very positive.