The Louisville researchers noticed that dry counties had higher rates of meth lab busts, as well as higher rates of meth crimes overall. And the effect is significant: "if all counties were to become wet, the total number of meth lab seizures in Kentucky would decline by about 25 percent," they found
TL;DR legalizing pot shows a statistically significant drop in pain medicine abuse. 25% fewer OD deaths due to pain killers in Colorado.
Prohibition only feeds crime and gangs and the mortician.