Phthiocol, also known as menadione, is a synthetic form of vitamin K3. It functions as a precursor to vitamin K2 and is involved in the carboxylation of proteins essential for blood clotting and bone health. Used primarily in animal nutrition to prevent vitamin K deficiency, promote growth, and as a coccidiostat in poultry feed. It also finds applications in cosmetics as an antioxidant and in pharmaceuticals for treating hemorrhagic conditions, though human use is limited due to potential toxicity.