Depending on who is interviewing you, the question may never come up. It is best to be prepared with an answer. Frankly, if you say you were an alcholic and recovered in September of 2002, it will leave some doubt in the interviewers mind if he is getting a reliable employee. As Artbrooks pointed out, in the U.S. you could sue if that was the reason they did not hire you, but you will need to prove that was the case, and that can be quite difficult to do - unless they are stupid enough to say it or send you a letter stating that was the reason.

I had a friend that used to work for me. He was moving to Atlanta and put me down for a reference.   I gave him a good reference (which by the way, laws in the U.S. have changed - you should only confirm employment, other information could put you in a position of being sued if the candidate does not live up to your recommendation. Welcome to the litigious society we live in!).    My friend called me up to see if the company he appplied to had called me. I told them that they did and I gave a glowing recommendation, I said that when Tim showed up sober he was the best employee I ever had.   There was silence on the phone. Of course I was kidding.