oh how I hate that drug.
you really need to stay away from them, they will do whatever they want and theres not a thing you can do. I assume you have tried to talk to them already and from the sound of it, it may not change.
be careful of them, drug addicts can say things that they know you want to hear in order to get you to do what they want.
don't lend money, don't give them anything including access to your home or your things. they will steal them, yes your best friend will steal from you. If you were laying on the street dying and you had $10 in your hand they will take the money before helping you. it's not them its the addiction, they can't help themselves.
so cross your fingers and say lots of prayers
sorry for sounding so mean but its the way it is
good luck