Question: I have heard various things about drinking on Purim. Is it an actual requirement?
Answer: The Gemara (Megilla 7b) teaches that one should drink enough on Purim that one can no longer tell the difference between cursed is Haman and blessed is Mordechai.
While some rishonim (Rif Megillah 3b; Tur OC 695:1) read this Gemara literally, many other rishonim and acharonim interpret this statement differently. Thus, the Rema (Darkei Moshe 695:1) writes that the Gemara is referring to a particular piyyut. One would need their full wits in order to be able to sing the lyrics properly, and even a little drink could confuse them (See Aruch Hashulchan OC 695:3; Kaf Hachaim OC 695:16).
The Baal Hamaor (Megilla 3b) and Ran (Megilla 3b) quote Rabbeinu Ephraim who write that as the Gemara continues with a story about the dangers of drinking on Purim, the maskana (conclusion) is that one should not drink. The Beis Yosef (OC 695:1) adds that there is no greater sin than being intoxicated which could lead one to transgress the most severe aveiros.
Rambam (Megilla 2:15) writes only that one should drink more than usual which will cause him to sleep. Simply, when asleep, one can no longer tell the difference (See Rema OC 695:2; Mishna Berura 695:5).
The Shaarei Teshuva (695:2), Chayei Adam (2:155:30) and Mishna Berura (695:4; Biur Halacha 695:2) all stress that one must not drink if doing so may prevent them from performing mitzvos such as davening, netilas yadayim, reciting berachos and the other mitzvos of Purim.
In conclusion, one must not drink at all if it will cause them to abandon any mitzvos or if they think they may drink too much.