I have often wondered about this. It would certainly pull the rug out from under the dealers and smugglers. But if their lucrative businesses dried up, would they not turn to other forms of crime?   An experiment in Holland issued heroin to addicts daily at a special centre, and they could hold down a job and function in society. Meanwhile, their intake was monitored and slowly reduced. Also, the drug administered was not dangerously adulterated, and the needles were sterile. But none of this explains why someone takes drugs in the first place. Or even goes back on to eg heroin after having been clean for a few months. That has always puzzled me.