“The jovial character of this feast is illustrated in the saying of the Talmud (Megilla 7b) stating that one should drink on Purim until he can no longer distinguish between (ad delo yada) the phrases, arur Haman (“Cursed is Haman”) and baruch Mordechai (“Blessed is Mordecai”). In Hebrew these phrases have the same gematria (“numerical value”), and some authorities, including the Be’er Hagolah and the Magen Avraham, have ruled that one should drink wine until he too drunk to calculate these numerical values.
“This saying was codified by Rabbis Isaac Alfasi (the “Rif”), Asher ben Jehiel (the “Rosh”), Jacob ben Asher (the “Tur”), Shulchan Aruch, Orach Chayim 695, and is interpreted simply (as explained above) by the Chatam Sofer. This interpretation of the Talmudic statement, or the acceptance of the statement itself, is disputed (for various reasons) by the Tosafists (based on the Jerusalem Talmud), Maimonides, Rabbeinu Ephraim, Ba’al HaMa’or, Nissim of Gerona (the “Ran”), Orchot Chaim, Be’er Hagolah, the Magen Avraham, Rabbis David HaLevi Segal (the “Taz”), Moses Isserles (the “Rema”), Vilna Gaon, the “Maharsha”, Rashash, Tzeidah LaDerech, Hagahot Maimoniyot, Ra’avyah, Korban N’tan’el, the Bach, the Maharil, P’ri M’gadim, Kol Bo, Chochmat Mano’ach, the Mishnah Berurah and others. These authorities all advocate drinking wine in some quantity, but all (except Hagahot Maimoniyot and Ra’avyah) discourage the level of drunkenness suggested by the Chatam Sofer. The Rema says that one should only drink a little more than he is used to drinking, and then try to fall asleep whereupon he certainly will not be able to tell the difference between the two phrases indicated by the Talmud. This position is shared by the Kol Bo and Mishnah Berurah, and is similar to that of Maimonides.”
— from Wikipedia