Regardless of whether this study would claim pot is harmful or harmless, this study can conclude nothing of the sort. They only study correlations, and only amo

Regardless of whether this study would claim pot is harmful or harmless, this study can conclude nothing of the sort. They only study correlations, and only among people who had already chosen to smoke or not smoke pot (this is a general limitation that is difficult to avoid, of course). What I found especially annoying is the hand waving assertion about brain "damage", without finding any actual functional differences. In effect they have merely found "differences", and they shouldn't be so eager to attach value judgments to them. Perhaps the paper is more careful than this press release. The flip side to your comment is that because pot is a politically charged topic, one should be extra critical of any studies, because it becomes more likely that people have a vested interested in certain outcomes. Add to that the fact that law makers can probably put more weight on their side of the story (because money), and you have the reason why liberals may be extra suspicious about studies purporting to show harm.