When
quaffed, this
potion gives enough
XP to raise your
NetHack character to the next
level. If the
potion is
blessed, it adds enough to get you halfway through the next level. These
potions are difficult to find and are the only alternative to eating
wraith corpses to gain levels past about 20.
The cursed version, true to the tradition of diabolical machinations which has come to characterize the Dev Team, causes you to rise through the ceiling of the level you're on. You "gain" a dungeon level. Aargh.
If this potion is dipped into a potion of extra healing, the result is a potion of full healing.