Phytomenadione, also known as vitamin K₁ or phylloquinone, is a vitamin found in food and used as a dietary supplement. It is on the World Health Organization's List of Essential Medicines.

As a supplement it is used to treat certain bleeding disorders. This includes warfarin overdose, vitamin K deficiency, and obstructive jaundice. It is also recommended to prevent and treat vitamin K deficiency bleeding in infants. Use is typically recommended by mouth, intramuscular injection or injection under the skin. When given by injection benefits are seen within two hours. Many countries in the world choose intramuscular injections in newborn to keep them safe from severe bleeding (VKDB). It is considered a safe treatment and saves many children from death and severe neurologic deficit every year.

Side effects when given by injection may include pain at the site of injection. Severe allergic reactions may occur when it is injected into a vein or muscle, but this has mainly happened when large doses of a certain type of supplement containing castor oil were given intravenously. Use during pregnancy is considered safe, use is also 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. In 1943 Edward Doisy and Henrik Dam were given a Nobel Prize for its discovery.