Is there a way to inform someone's psychiatrist that they are drinking with the sedatives being prescribed?

Basically he is on the same combination that killed Heath Ledger everyday. His doctor obviously doesn't know he drinks or he/she wouldn't have prescribed these drugs. I know the doc. can't talk to me about the client. But can I talk to the doc. about the client? I want to keep him from killing himself. I have already tried to deal with him directly about his problems and it didn't help.