Sprig of wolfsbane
Eating a sprig of wolfsbane will cure lycanthropy.[1]
Wolfsbane is a vegan food, and is also suitable food for herbivorous pets.
Priests begin the game with a sprig of wolfsbane.
Wielding wolfsbane has no effect on lycantropes or wolves (as opposed to garlic or other banes). You can't use wolfsbane to poison weapons and it will not poison you if you eat it.
This is in fact a major case of NetHack is not real life, because wolfsbane in real life is very poisonous (so don't eat it in real life), and the name comes from the fact, that it was used to poison wolves. Wolves were often killed by Christians because of two reasons : First, wolves sometimes prey on lifestock and were considered a pest - second , wolves were considered sacred by Germanics (for example Wotan is accompanied by the wolves Geri and Freki), and the monotheist Cristians desecrated their values, by killing wolves (or chopping down old oaks which were used to whorship Tyr).