I live in Sao Paulo, Brazil. We have quite bad drug abuse issues as well.
I have helped a group that rescued several people (I believe most with drug addiction) from the streets[1]. What they do, and several other groups, and also government institutes do, is offer voluntary recovery programs that are legitimately very good. You can go there and they'll take care of you, including professional psychologist/psychiatrist support (and medicine to help get off drugs); in the main institution we're working with[2], former homeless and former drug dependents help directly in welcoming people. I'm not sure that's the whole solution to the drug problem, but I think it's part of the solution -- getting out in the streets, offering help to the homeless and addicts, and if they want, taking them somewhere that'll offer shelter and recovery from addiction. [3]
There's one rule in those places: you can't go in with drugs with you. Of course, if the person becomes too violent then they might not be able to deal with them either.
Please, go out there and help (while staying safe too, preferably in a group) -- or help institutions that do this kind of work (like we say, everyone can play a role, be it in a kitchen, on the streets, or with donations). I think it's groups like this that keep things from falling apart.
There are many people on the streets for whom drugs are just a quick escape mechanism, and have economic issues, mental health issues, or health issues (or all together), and a compassionate community/institutions that helps everyone recover is what really is needed I think.
Pretending they don't exist or as a friend calls "shuffling them around" doesn't work.
[1] Our group offers a meal once a week (Sunday nights, where they have difficulty finding something to eat), and we offer taking them off the streets. It's incredible what genuinely caring about people will do: I've seen people cry when you hand them a plate of food.
[2] It's this one: https://www.missaobelem.org/; This one is state funded and excellent as well: https://hub.spdmafiliadas.org.br/ (called HUB)
[3] Other important parts being, educating people about the tragedy of drug abuse, and providing community and support so they don't resort to drugs, and also preventing selling.