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Overview: Vitamin K is taken by mouth to increase low levels of vitamin K and to reduce the risk of bleeding in people with certain blood clotting problems. Vitamin K is usually well tolerated. Serious side effects are rare. Before taking vitamin K, tell your health care provider about any health conditions you have or medicines you are taking.

Uses

What is vitamin K (oral) used for?

Vitamin K is commonly used to reduce bleeding risk and correct certain blood clotting problems. These blood clotting problems can be from any of the following.

  • Medicines that block the activity of vitamin K in your body, such as warfarin, which is a blood thinner
  • Other medicines or health conditions that affect your body’s ability to absorb, process, or use vitamin K

Vitamin K is also used to increase low levels of vitamin K to support healthy bones and normal blood clotting.

These uses may vary depending on the specific vitamin K product you are taking.

Vitamin K may also be used for other conditions as determined by your health care provider.

How does vitamin K (oral) work (mechanism of action)?

Your body uses vitamin K to keep your bones healthy and make certain proteins, called clotting factors. Clotting factors help your body form blood clots. Forming a blood clot is your body’s way to stop bleeding and heal from wounds or injuries.

People with certain health problems, or people who are taking certain medicines, may not absorb enough vitamin K from foods. Giving vitamin K can help to increase vitamin K levels.

Warfarin, a blood thinner, works by directly blocking vitamin K in the body. Some people use this medicine to reduce the risk of dangerous blood clots. In people who take too much warfarin, or who need to have an urgent procedure or surgery, taking vitamin K can help to reverse the effects of warfarin.

In the United States, most people get enough vitamin K from their diet. It is found in vegetable oils, leafy green vegetables, certain fruits, meats, eggs, and soybeans. The normal bacteria that live in your gut also make vitamin K that your body can use. For most adults, the recommended daily intake of vitamin K is 90 to 120 micrograms. But some people either do not get enough from their diet or have trouble absorbing it, which can lead to low levels of vitamin K. When this happens, you can take vitamin K to replace what you are not getting from your diet or the bacteria in your gut.

How is vitamin K (oral) supplied (dosage forms)?

Brands and other names

  • Aqua-Mephyton
  • Mephyton

Dosage forms and strengths

  • 5 mg oral tablets

Vitamin K is also available as a dietary supplement in various strengths and dosage forms and as a prescription in an injectable form. See also: Vitamin K injection (phytonadione)

How should I store vitamin K (oral)?

Storage requirements for vitamin K may not be provided with the product packaging. Most medicines should be kept in a cool, dry location that is out of reach of children and pets. Store it in the original carton to protect it from light. Vitamin K is degraded by light. If you have questions about how to store vitamin K, ask your pharmacist.

Side Effects

What are the most common side effects of vitamin K (oral)?

Vitamin K is usually well tolerated. Tell your health care provider if you have any side effects that bother you.

Contact your health care provider if you think you are having a side effect of a medicine. In the U.S., you can report side effects to the FDA at www.fda.gov/medwatch or by calling 800-FDA-1088 (800-332-1088). In Canada, you can report side effects to Health Canada at www.health.gc.ca/medeffect or by calling 866-234-2345.

What are the serious side effects of vitamin K (oral)?

While less common, the most serious side effects of vitamin K are described below, along with what to do if they happen.

Severe Allergic Reactions. Vitamin K may cause allergic reactions, which can be serious. Stop taking vitamin K and get help right away if you have any of the following symptoms of a serious allergic reaction.

  • Breathing problems or wheezing
  • Racing heart
  • Fever or general ill feeling
  • Swollen lymph nodes
  • Swelling of the face, lips, mouth, tongue, or throat
  • Trouble swallowing or throat tightness
  • Itching or skin rash
  • Bumps on the skin called hives that can be red, pink, white, or brown depending on your skin tone
  • Nausea or vomiting
  • Dizziness, feeling lightheaded, or fainting
  • Stomach cramps
  • Joint pain

Warnings & Precautions

Who should not use vitamin K (oral)?

Allergies to Ingredients. People who are allergic to any of the following should not take vitamin K.

  • Aqua-Mephyton
  • Menaquinone
  • Mephyton
  • Phylloquinone
  • Phytonadione
  • Vitamin K
  • Any of the ingredients in the specific product

Your pharmacist can tell you all of the ingredients in the specific vitamin K products they stock.

What should I know about vitamin K (oral) before using it?

If vitamin K was prescribed to you by a health care provider, take it as prescribed. If you are taking over-the-counter (OTC) vitamin K, follow the instructions that come with the product or take it as your health care provider recommends.

Do not share vitamin K that was prescribed for you by a health care provider with other people, even if they have the same condition as you. It may harm them.

If you are taking a liquid form of vitamin K, use an accurate measuring device to measure your dose. A household spoon is not an accurate measuring device and may cause you to take the wrong dose. Ask your pharmacist what measuring device to use.

Keep vitamin K out of the reach of children.

What should I tell my health care provider before using vitamin K (oral)?

Tell your health care provider about all of your health conditions and any prescription or over-the-counter (OTC) medicines, vitamins/minerals, herbal products, and other supplements you are using. This will help them know if vitamin K is right for you.

In particular, make sure that you discuss any of the following.

Current and Past Health Conditions. Tell your health care provider if you have any of the following.

Other Medicines and Supplements. Vitamin K may interact with other medicines and supplements. Before taking vitamin K, tell your health care provider about any prescription or over-the-counter (OTC) medicines, vitamins/minerals, herbal products, and other supplements you are using. See the Interactions section for more details.

Pregnancy. It is not known if or how vitamin K could affect pregnancy or harm a fetus. Tell your health care provider if you are pregnant or plan to become pregnant. Your health care provider will let you know if you should take vitamin K while you are pregnant or trying to get pregnant.

Breastfeeding. Vitamin K passes into breast milk. Tell your health care provider if you are breastfeeding or plan to breastfeed. Your health care provider will let you know if you should take vitamin K while breastfeeding.

Interactions

Does vitamin K (oral) interact with foods or drinks?

There are no known interactions between vitamin K and foods or drinks.

It is unknown if drinking alcohol will affect vitamin K. Vitamin K can be used to reduce bleeding risk from certain blood clotting problems. Alcohol can increase your risk of bleeding. It is best to limit the amount of alcohol you drink.

Does vitamin K (oral) interact with other medicines (drug interactions)?

Always tell your health care provider about any prescription or over-the-counter (OTC) medicines, vitamins/minerals, herbal products, and other supplements you are using.

In particular, make sure that you discuss if you are using any of the following before taking vitamin K.

  • An antibiotic, which is a medicine used for bacterial infections
  • Warfarin, which is a blood thinner
  • A bile acid sequestrant, such as cholestyramine (Prevalite), colestipol (Colestid), or colesevelam (Welchol), which is a medicine to lower cholesterol
  • Orlistat (Alli, Xenical), which is a medicine used for weight loss

This may not be a complete list of medicines that can interact with vitamin K. Always check with your health care provider.

Does interact with other drugs you are taking?

Enter your medication into the WebMD interaction checker

Overdose/Missed Dose

What should I do if I accidentally use too much vitamin K (oral)?

If you or someone else has used too much vitamin K, get medical help right away, call 911, or contact a Poison Control center at 800-222-1222.

What should I do if I miss a dose of vitamin K (oral)?

If you miss a dose of vitamin K, take it as soon as you remember. If it is almost time for your next dose, skip the missed dose and only take the next dose. Do not take double or extra doses.