Note that I'm mostly for legalized drugs. I just have heard this data and I don't have an answer to it. My impression is I just take it on faith that less criminalization will be a net positive but I don't know that's for sure.
Alcohol is a terrible drug and kills you in a known fashion, but you don't buy a can of beer from the store and then die from drinking that can because it was actually bleach, because alcohol is legal and regulated product. Drug addicts hooked on oxy getting their fix off the street are getting killed because street supply is dirty and inconsistent. Having a consistent supply would lead to fewer accidental deaths from unknown supply.