Giving someone money to buy drugs

I regret to inform you that my younger brother is a drug addict from many years. His wife has also left him because of this. He has a 14 year old daughter and my mother is taking care of him. We have tried many times to treat him for drug addiction but he again starts taking drugs. He says that he cannot even move without drugs. My mother is suffering very much seeing his condition. She cannot see him dying in front of her eyes. She has to give him money for drugs and she feels that we should also give him money for drugs otherwise he would die. My question is, can I give him money for drugs or is it a sin? Please answer me as I am in a dilemma.