Poor people would no longer need to steal for their daily dose, all would be provided by the state. The illegal market would disappear since you can't compete with $0 price.
You would have hard drugs vending machines on street corners, that you can access with your government provided drug card.
IMHO, if a person is prepared to habitually commit crime to fund their habit, it's time to get them off the drugs, by force if necessary.
Develop 'rehab jails' for addicts, where they can be kept off the streets, tapered off the drugs, and given decent treatment for underlying mental health issues.
You would probably still need to get these people into treatment, and prevent them from selling the drugs onwards, and prevent new people from getting on drugs.
The invisible hand of the market could be a powerful ally in all of these, but we prefer as a society to do things in a difficult way that has never worked.