All this doesn't mean that you can't be compassionate if someone is unfortunate enough to be mired in drug and alcohol problems. You can certainly say some version of this:
"If there's anything going on at work that's affecting your performance, please let me know. If there's anything that's going on in your personal life that's affecting your performance, that's none of my business but we do have employee assistance so you may want to contact them."
And then, of course, if they do come up with some specific complaint about their drug or alcohol issues, you can be empathetic and deal with that. You want to open that door but not walk through it. Unless you're a trained medical professional, therapist, or recovering alcoholic or addict yourself, you want to stay away from giving advice in this area. Simply stay compassionate but focus on performance and enforce the specific boundaries and performance standards that your workplace requires. It can be very tempting to want to rescue someone in this situation but you won't be doing any good by trying to handle it yourself.
Lynne Eisaguirre is a former practicing employment attorney whose media credits include CNN Headline News, ABC News, Bloomberg TV, U.S. News & World Reports, The Boston Globe and The San Francisco Chronicle, among many others. She presents speeches and workshops on management issues to clients such as Bristol Myers Squibb, Harley Davidson, Sun Microsystems and Southwest Airlines. You can reach Lynne at: http://www.workplacesthatwork.com.