The British have had a system of heroin maintenance since the 1920s. For decades it supplied a few hundred addicts nationwide, most of whom were doctors themselves. It was de-emphasized considerably during the 1960s-1980s as a result of the U.S.-led war on drugs.
I was just about to mention Portugal. When you give people help and a safe option to quit then many do quit.
https://en.wikipedia.org/wiki/Heroin-assisted_treatment