I've told people I'm close to that I'm going to AA and trying not to drink anymore, but I haven't really used the term "alcoholic" and I haven't promised anyone that I will never drink again; I'm not a fortune teller.
You can always use the "health reasons" line. High blood pressure, bad reaction with medication you're on...Really, if you say "I can't drink for health reasons," it's nobody's business what those health issues might be. In my case, it will lead to my death, and that's not very healthy.
At work (I work in a restaurant where lots of employees drink and I know and am friends with most of the regulars) I've told most people that I'm trying not to drink till the end of the school semester. It's not a lie, and I do need to focus on my studies. So I reckon when the semester ends and I'm still not drinking (God willing) I'll just tell everyone that I feel so good being sober that I'm just gonna keep that going. That's not a lie, as long as I make it happen.
You could tell people you're trying not to drink till X date for X reason. If you reach that date, you can then say that your body and mind feel so good without alcohol that you just decided to run with it.