I'm not going to let my brother borrow one of my prescription painkillers
Does he need one for pain? What is going on?
No, that's not the reason. He is a drug addict and will probably sell them for money
It is smart not to give others medication that they haven't been prescribed. Painkillers can be dangerous especially for an addict. You should see if he is willing to go into treatment.
He blows through all of his painkillers, I don't want to give him anymore of my prescription.
It is really good you are standing your ground with this. Have you tried to get him help for his addiction? I think you're doing the right thing.