Does Prolonged Overdose Of Ambien For OCD Cause Problems?

hello I live with my brother and i need to ask someone a question. My brother has been taking ambien for over 3 years on a daily basis. He now takes 4 times the normal amount. I am worried and not sure what to do. My brother always had trouble sleeping and he has OCD and he says ambien also helps him calm down. My main question is at this rate could he really hurt himself by doing this such as overdose or anyother. When I get on him for taking ambien everyday he tells me that its not like he's doing illegal drugs he says its my buisness and my docter perscribes them to me. As a brother I worry and not sure what to do