Question on Ethics - Health care workers?

This has not happened to me but now that I am an Rn student I am going to be faced with ethical situations that I would normally not take a stance on. For example, If I knew someone at work was a drug user I would not deal with the issue at all. Esp. if they do not ask for help and co-workers usually do not. I tend to have a "live and let live" personality. But in the health care setting if another Rn is taking drugs for personal use and i just happen to see that person sneak out narcotics or something serious like that I would have a responsibility to turn that person in for several reasons. How would you handle it?!