First I wanna say initially when I responded pretty much saying "who cares", I didn't even read the other posts, so I wasn't going along with the "group mentality". After i posted then I read what everyone else said.
Second, if I saw someone sleeping one the job I would first ask them if they are ok and if they are feeling well. I would NOT immediately go tattle on them.
From the little info you gave about the situation, really sounds like it has no real affect on your job or life. You are just making this your problem, when who cares! Focus on your life, your family, friends, better those relationships. Don't worry about those that aren't really involved with you.
I know someone that is addicted to heroin. If I had your attitude this person would be in jail. I am not really that close with the person, but I would be there if they every need to reach out for help. In reality though, at the end of the day, whether this person shoots up or not, does not affect my life. I am glad I don't because that could get me swept up into a world I don't want to go into. Do I think that it is a good decision that they do heroin? Not at all! It's also not my business to try and control what they choose to do with their life, so I don't mess with it. I focus on bettering my life and surrounding myself with loved ones and creating a world that works for me, and it is not only the best decision for myself, but for everyone.