Q.  A Cohen took part in a Kiddush after davening on Yom Tov and had some liquor. As he was going home, he was asked by a late minyan to say Birchas Kohanim for them, as they didn’t have any other Cohen available. Could he do it?
A. Shulchan Aruch (O.H. 128: 38) rules that a Cohen that drank a Revi’is of wine, should not be part of Birchas Cohanim, since it is comparable to the Avoda done in the Beis Hamikdash.
Mishna Berura quotes, the permissive opinion of the Mogen Avrohom, that a Cohen may bless when drinking liquor, even if he is somewhat drunk, even if he is unable to speak respectfully in front of a king. Although, the above does not apply to Tefila, where we are stringent.
However, Mishna Berura mentions that many Poskim disagree, and maintain that if one drank enough to be unable to speak respectfully in front of a king, he should not recite Birchas Cohanim.
Piskei Teshuvos (ibid. 80), quotes that the minhag is to avoid any kind of Kiddush before the blessing.
However, Horav Shlomo Miller’s Shlit’a opinion is that in this particular case since there is no other Cohen available, if he is able to speak respectfully in front of a king, he may proceed with the blessing.
Rabbi A. Bartfeld as advised by Horav Shlomo Miller and Horav Aharon Miller Shlit’a