The problem with all of these ‘studies’ is that they always mix apples and oranges, with an occasional watermelon thrown in.
Take a few unadulterated marijuana seeds, toss them into the ground, and come back in a few months. Roll those leaves up and smoke them. Yes people have being doing so for over a thousand years, with relatively minor if any negative results.
But do you think that is what is sold on the street? Hell no. Kids would refer to it as stink weed. Your throat would get sore before you could smoke enough of it to REALLY get high.
No, what is sold on the street is specially raised, processed, and doctored with who knows what to dramatically increase the potency. What are the possible harmful effects? Who the heck could know that, since nobody knows what’s been done to it in the first place!
Sorry, but it is EXACTLY like every other drug sold on the street - a total unknown. And people use it at their own risk.
Another good argument for relegalization - sellers of the legal drug alcohol don't doctor their product because legal products can be regulated.