Regarding cannabis use in Canada, we've seen in an increase in cannabis use disorder. We've also seen an increase in ER visits for psychosis related to cannabis. Legalization of cannabis hasn't decreased that.
However, a balance needs to be struck. Has that downside been outweighed by the upside of decreased criminalization of people who are using cannabis? I'd leave it to policy-makers to decide that, but there do seem to be upsides and downsides for legalization.