(biochemistry, pharmacology) A yellow oily naphthoquinone C₃₁H₄₆O₂ that is obtained especially from alfalfa, cabbage, spinach, and other leafy green vegetables or made synthetically and that has a fast, potent, and prolonged biological effect. It is essential for the blood-clotting process, effective orally, and useful especially in treating hypoprothrombinemia induced by anticoagulant drugs (trademark Mephyton).