At least some content in this article is derived from information featured in Harry Potter: Hogwarts Mystery. Spoilers will be present within the article.
Cowbane is the common name of Cicuta virosa, a poisonous plant. It can be used as a potion ingredient, and a "splash" of what would presumably be an infusion of cowbane was an ingredient in the recipe for Shrinking Solution listed in Book of Potions. It can also be used as an ingredient for Doxycide.