Phytomenadione, also known as vitamin K1 or phylloquinone, is a vitamin found in food and used as a dietary supplement. As a supplement it is used to treat certain bleeding disorders. This includes in warfarin overdose, vitamin K deficiency, and obstructive jaundice. It is also recommended to prevent and treat hemorrhagic disease of the newborn. Use is typically recommended by mouth or injection under the skin. Use by injection into a vein or muscle is recommended only when other routes are not possible. When given by injection benefits are seen within two hours. Common side effects when given by injection include pain at the site of injection and altered taste. Severe allergic reactions may occur with injected into a vein or muscle. It is unclear if use during pregnancy is safe; however, use is likely okay during breastfeeding. It works by supplying a required component for making a number of blood clotting factors. Found sources include green vegetables, vegetable oil, and some fruit. Phytomenadione was first isolated in 1939. It is on the World Health Organization's List of Essential Medicines, the most effective and safe medicines needed in a health system. The wholesale cost in the developing world is about 0.11 to 1.27 USD for a 10 mg vial. In the United States a course of treatment costs less than 25 USD. In 1943 Edward Doisy and Henrik Dam were given a Nobel Prize for its discovery.