When it comes to drugs, we need to admit that there will be a certain number of people who are going to use drugs no matter what we do. As with unemployment, we need to pick a number -- say 5%.
When we reach that number we declare victory then spend only enough each year to maintain that number.
We would have to deal with druggies as we do now with drunks. Some druggies function well just as some drunks function well right now. The rest have to go to a drying facility...and if that fails, they go onto the streets. They used to go to hospitals and sanatoriums until the libs declared that holding drunks in those kinds of places was somehow a violation of their rights. So they live on the streets.
I don't think that there would be so many people doing drugs after legalization as many think. I don't know one person who would go out and do a line of cocaine if it suddenly became legal, and I bet most people here don't know anyone who would either.