Long ago, I took an vow to (among other things) not knowingly drink alcohol. To this date, I have upheld that idea. However, if the wine used in the Eucharist is no longer wine, but is now the blood of Christ, then drinking it would not break my oath. Still, it looks, smells, and (I assume) tastes like wine, thus I have not drank of that cup, but instead (during times when it is offered) venerate it by raising up the chalice and bowing my head.
That said, I think I would have more of a problem if I was offered a cup full of a liquid that looked, smelled, and tasted like blood.