Repression, repression, repression. The three factors associated with MJ regulation in Canada. Repression in the past, when in 1923 MJ was outlawed without even a vote in Canada; repression of evidence that shows MJ does not harm youth brains. The studies that suggest otherwise have not been designed to determine causality, which would require a longitudinal design to establish temporal precedence. 

The confounding factor is alcohol abuse by youth, even modest alcohol abuse may be associated with morphological changes and may represent an important confounding variable in studies on the effects of cannabis. And repression tomorrow, with an emerging picture of Bill C-45 ("the Cannabis Act") as a series of clampdowns on civil liberties: enshrining extraordinary stop/search/seize powers for cops; justification for oppressing youth; and bizarre civil forfeiture laws that effectively deal police into the production game. 

Legal weed? Yuck!