Haegarda is a man-made form of a protein called C1 esterase inhibitor (C1-INH), that is injected subcutaneously (under the skin) to prevent angioedema attacks in adults, adolescents, and children over the age of 6 with hereditary angioedema (HAE). Haegarda replaces missing C1-INH, preventing the generation of bradykinin and other substances that increase the permeability of blood vessels.