First thing, recognize this is not your problem, and you cannot fix it. They have to fix it. I think sitting down and telling them "hey look, I know you are taking more than you should be, and I'm very concerned about you." SET BOUNDARIES and stick to them! ie; if i find you have been stealing medications or doing something illegal-I'll have no part of that and you'll have to find somewhere else to live. Remember, by allowing them to continue in doing this, you are only helping them get worse every day. This may sound a bit crazy, but go to an Ala-non group. These groups work together to help YOU maintain your sanity in living with someone with alcoholism or addiction. They can teach you how to take control of your own life and allow the others to do the same. You don't have to feel like you need to fix this. It's not your problem to fix. But definitely let them know what you know, what you see, and that you aren't wearing a blindfold. Also tell them what you are NOT going to put up with anymore.