Sorry, I'm a workaholic

I've been doing some thinking, and I'm wondering why we don't treat all addict with the same respect we show alcoholics. An alcoholic can turn down a drink with a simple, "Sorry, I'm an alcoholic" (and the person who offers the drink feels really bad). Why can't I say to my boss when she gives me more work, "Sorry, I'm a workaholic." (She might even feel bad about trying to make me do work.)