May on drink alcohol before praying?
The Shulhan Aruch (O.H. 99:1) says that if one drank a Revi’it (about 86 mL) of wine one may not pray until the effects of the wine subside. If one drank greater than a Revi’it and can maintain the composure needed to speak before a king, then if one prayed, one would fulfil one’s obligation to pray. If one drank to the point where one would not be able to maintain the proper composure, one’s prayer is considered an abomination and if one prayed one would need to repeat the prayer when the effects of the wine subside. The Mishna Berura (M.B., O.H. 99:1) says that this rule also applies to other alcoholic beverages. Rabbi Ben Zion Abba Shaul (Or Lezion, vol. II, ch.45, § 28) says that since some alcoholic beverages, such as Arak, have a higher concentration of alcohol than wine, the aforementioned amounts one would be able to drink before praying would be less than a those for wine.
The Rama (ibid:3) says that nowadays people are more lenient with regards to drinking since contemporary wines are not as potent as those in the past, and because it is common to pray from a Siddur, which ensures at least a modicum of concentration. Nevertheless, one should know one’s limits and should not pray if one feels intoxicated. The Kaf HaHaim (K.H., O.H. 99:5) cites an opinion that if one is intoxicated, one should not pray even if one will miss the the time for prayer.
Rabbi Baruch Toledano questions the practice in Morocco to drink alcohol while eating and then pray Minha. Citing the Rama, he says that alcoholic beverages these days are milder than before and everyone is accustomed to using a Siddur, and therefore the practice is permitted. It goes without saying that this only refers to a case when the congregants are able to maintain the requisite composure and focus.
Summary: If one drank alcohol one may not pray until the effects of the alcohol have subsided.