Vitamin K3, molecular model. The chemical formula for vitamin K3, now called menadione, is C11.H8.O2. Atoms are represented as spheres and are colour-coded: carbon (blue), hydrogen (gold) and oxygen (red). Menadione is a provitamin, a precursor to vitamin K2. Due to its high toxicity, its use as a nutritional supplement for vitamin K has been banned in most countries. Large doses can cause haemolytic anaemia (the destruction of red blood cells) in adults and brain damage, liver damage and even death in neonatal babies. However, low doses of menadione are still used in many countries as an inexpensive micronutrient supplement for livestock.