Leave your brother to die on the street, cold and hungry and ignored. Of course.
After sleeping on the street for one night, the brother might also choose to spend his money on rent rather than weed the next time around.
Do you have any evidence for that? I would wager it leans in the other direction: sleeping on the street leads to other negative behaviors, in aggregate.
You might want to check on the price of weed vs rent in a typical city. The brother is unlikely to forgo the weed if doing so just means he's sleeping in the streets sober instead of high.