Most places that focus on treatment rather than punishment see drops in all the relevant stats for deaths, crime, health issues, etc. related to drugs usage. And even drops in drug abuse itself. The one thing that has never really worked and continues to create endless amounts of misery is the war on drugs and all the collateral damage it causes.
I totally believe that treatment should be the focus for drug users; the only focus, even. What I'm having trouble believing is that convenient access to drugs would not result in net-harms that are worse than those inflicted by (imperfect attempts at) holding people accountable for selling these chemicals to the vulnerable, irrespective of whether or not those people are pharmaceutical companies or cartels.
I would like to see evidence that jurisdictions in the developed world that stop prosecuting dealers for freely selling what I'd call "hard drugs", e.g. opiates and amphetamines, see their population's well-being improve, on the whole - if there has ever been such a jurisdiction.
It never worked. Not even a little bit.