Imagine your favorite cream-based liqueur or cocktail. Now imagine its alcoholic strength increased far-beyond reason and throw in a little magic. "Heady" is just too pale a description for the brose of the Nac Mac Feegle.
Now, brose is made across the Multiverse by people who eat the oats and brew the barley. Its style varies from a sauce to a beverage, but there are always: oatmeal solubles, honey, and whisky. Cream is often added, and herbs and spices are optional. Atholl Brose is a dessert sauce made to a thicker consistency; beverages may contain either much more whisky, or water.
The Nac Mac Feegle know something about strong drink; in fact, they'd be happy to study nothing else, with the occasional break for "fightin' an' snafflin' coo-beastie." They brew brose both as a ceremonial and medicinal beverage to cure whatever ails them (and, perhaps, because they like it); their recipe calls for very strong whisky and ...herbs, lots and lots of herbs.
It was powerful enough to save the young King Verence II from vampirism. Feegles resemble bees somewhat in terms of their social and biological structure, and brose may correspond vaguely to royal jelly.