Can one use Grape Juice for Ad dlo Yoda on Purim?
It seems pretty clear that 'Ad DeLo Yada' is fulfilled through alcohol, not wine per se. I've heard that wine is preferable, and even that one does not fulfill the requirement if one gets drunk on whisk(e)y. This seems very strange to me, as the point is to get so joyfully drunk that one is unable to distinguish between two polar opposite characters. Unless one gets bumped on the head with the bottle, I'm not sure how this would be achieved with grape juice (and even then, I'm not sure that would qualify - so don't try it at home or anywhere else).
The question as to whether this is truly a Jewish value, and what a recovering alcoholic, a teenager and anyone concerned with the dangers of drinking (with or without driving) is supposed to do on Purim is an entirely different question. But any straightforward interpretation of the "Mitzvah" can lead to only one conclusion - actual drunkenness by means of alcohol.
There are no sources cited, but this article from Ohr Yerushalayim claims that R' Shlomo Zalman Auerbach said that grape juice does not suffice.
For additional reference, see Rabbi Dov Fischer's article here on the subject: http://www.jewishjournal.com/purim/article/drinking_does_not_drive_the_purim_celebration_20110311/
He states, in part, "Our greatest Rabbinic Sages over the centuries have wrestled with the dichotomy, looking to harmonize the themes. One Rabbi, the Magen Avraham, noted that the gematria numerology – the sum of the letters of the words, with each Hebrew letter having a numerical value – of “Arur Haman” (Cursed is Haman) is 502. And the letters comprising “Barukh Mordechai” (Blessed is Mordechai) also equal 502. (See M.A. Comment 3 on Shulchan Arukh, Orach Chaim 695:2.) So, he said, drink only until you can’t do the tally of those numbers in your head. Another taught that you should drink only enough to make yourself a bit drowsy, which will lead you to fall asleep, and – unless you have a Purim dream – you then will be in state where you don’t know the difference between Haman and Mordechai. (See, e.g., Ram”a on Shulchan Arukh 695:2.) A similar approach is taken by Rambam (Maimonides). (Mishneh Torah, Hilkhot Megillah 2:15).
"In recent years, as American culture in general, and our teen culture in particular, has grown depressingly coarse – witness television shows like “Jersey Shore” and “Skins” and a society where more people know the daily thoughts, so to speak, of Charlie Sheen and Lindsay Lohan than they do of their Congressional representative or the Poet Laureate of the United States – more rabbis than ever have called for bans on teen drinking during Purim and also have condemned the practice of certain outlier sects who would encourage drinking to the point of barfing on Main Street. Judaism despises drunkenness, and Rambam explicitly warned against it. (See, e.g., Mishneh Torah, Hilkhot De’ot 5:3; Hilkhot Sh’vitat Yom Tov 6:20)"
One does not fulfill the mitzvah of drinking with grape juice. Shevet HaLevi 10:107:2, Shalmei Moed page 288, Halichos Shlomo Moadim 19:footnote 76, Rivevos Ephraim 8:600
Source: Halachically Speaking 10:3 pg 12 (pdf)
The Shulchan Aruch (OC 695:2) writes:
One must become drunk on Purim until he doesn't know the difference between "arur Haman" and "baruch Mord'chay".
The Rama (ad loc.) adds:
But some say that he need not get so drunk: rather, he should drink more than his custom and sleep; because he's sleeping, he doesn't know the difference between "arur Haman" and "baruch Mord'chay".
One who does much or little — so long as he directs his heart to heaven!
On the Rama's words "and sleep; because he's sleeping, etc.", Mishna B'rura comments:
That's what's seemly to do.
(All translations are my own.) If one follows this ruling, that sleep is a way — the appropriate way! — to fulfill the "not know the difference" rule, then the question arises why one needs to drink at all. Once one finds out the reason for that, he can determine whether that reason is met by grape juice: maybe (and this is just conjecture) grape juice would suffice for "not know the difference", much as some people hold it does for kidush.
As always, consult your rabbi for practical guidance.