Halakhah for Taanit 30:1

And just like it is forbidden for a priest to come to the Temple on account of drunkenness, so is it forbidden for any man - whether priest or Israelite - to give a ruling when he is drunk. Even if he drunk the honey of dates or milk and his mind is mixed up, he should not issue a ruling; as in the section of "Wine and strong drink you shall not drink," it is stated (Leviticus 10:11), "And to instruct the Children of Israel." But if he gave a ruling about a thing that is explicit in the Torah to the point that the Sadducees (conceded) [know] it, it is permitted - for example, if he gave a ruling that a sherets (certain swarming animals) is impure or that blood is forbidden, or similar to them. And it is permitted for a drunk to read the Torah, and even laws and homilies (midrash) - and that is when he does not give a ruling. And if he was a sage that regularly gave rulings, he should not teach - as his teaching is [legal] instruction. If he drank only enough for a reviit and there was the smallest amount of water in it or he slept a little or he walked [the distance] of a mil, the wine has already passed and he is permitted to serve. But if he drink more than a reviit - even if it is mixed - if he a slept a little or walked on the way, it adds to his drunkenness. Rather he should wait according to his drunkenness until there is nothing at all left from his drunkenness. The [priests] of the shift were permitted to drink wine during the nights, but not during the days, of their week (Taanit 15b) - and even the other clans of the shift whose service was not on that day, lest the service be heavy for the clan of that day and they require other men from their shift to help them. But the men of the shift from that day are forbidden to drink both night and day, lest he drink at night and get up early for his service while his wine has still not gone away from upon him.