What is Vitamin K2? Uses, warnings & side effects

Medically reviewed by Keith Gardner, R.Ph.
Registered Pharmacist
Updated Dec 18, 2025  •  Published Dec 30, 2020
Fact Checked

Vitamin K was initially discovered as a nutrient involved in blood clotting. There are two forms of vitamin K: K1 (phylloquinone), which is found in plant foods like leafy greens, and K2 (menaquinone), which is found in dairy, fermented foods, and animal products as well as produced by gut bacteria.  

Vitamin K2 has been shown to play an important role in helping with osteoporosis, cardiovascular disease, inflammation, cancer, Alzheimer's disease, diabetes, and peripheral neuropathy. Vitamin K2 is available in the following dosage forms: tablet, sublingual tablet, capsule, liquid-filled capsule, liquid, and powder for suspension. It is often found in multivitamins or combined with other supplements such as vitamin D. Those taking blood thinners (e.g., warfarin) should keep their vitamin K2 intake consistent and avoid variations up or down to prevent drug interactions that may increase or decrease blood coagulation.

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Vitamin K2 overview

BRAND NAMES:

  • Vitamin K2

Generic Names:

  • Menaquinone

Uses:

  • Supplements such as vitamin K2 are given to people who may not get adequate amounts in their diet.

Therapeutic Classes:

  • Dietary supplement

  • Essential vitamin

Forms:

  • Tablet, sublingual tablet, capsule, liquid-filled capsule, liquid, and powder for suspension

How it’s taken:

  • By mouth

What is Vitamin K2 used for?

Vitamin K2 aids in blood clotting, aids with bone health by reducing fractures and improving bone quality in people with osteoporosis, and helps heart health by preventing calcium from depositing in arteries making it less likely to experience cardiovascular events such as heart attacks and strokes.

Key takeaways

  • Supplements such as vitamin K2 are recommended for people who may not get adequate vitamin K intake from food sources in their diet.

  • You should not take more of a supplement such as vitamin K2 than your healthcare professional has directed or more than the package label recommends.

  • For adults, a daily intake of between 100 to 300 mcg of vitamin K2 is recommended.

  • Do not take vitamin K2 if you are taking anticoagulants (blood thinners), such as warfarin, without the advice of a healthcare professional.

What form(s) does Vitamin K2 come in?

  • Capsules, liquid-filled capsules

    • 45 mcg

    • 50 mcg

    • 100 mcg

    • 180 mcg

    • 200 mcg

    • 300 mcg

    • 600 mcg

    • 620 mcg

  • Tablets

    • 100 mcg

    • 2,200 mcg

    • 5,000 mcg

  • Sublingual tablets

    • 100 mcg

    • 500 mcg

  • Powder

    • 90 mcg/9 mg

  • Liquid

    • 100 mcg/drop

    • 120 mcg/ml

What are common Vitamin K2 dosages?

  • For adults, a daily intake of between 100 to 300 mcg of vitamin K2 is often recommended.

How to take Vitamin K2

  • You should not use more of a vitamin supplement than your doctor has ordered or more than the package label recommends. Some vitamins, such as Vitamin K2, are fat-soluble vitamins and can build up in your body and may be harmful.

  • Follow the instructions on the package label if you are using this supplement without a prescription.

  • Swallow the tablet, extended-release tablet, capsule, or liquid-filled capsule whole. Do not break, chew, or crush it.

  • Dissolve the sublingual tablet under the tongue.

  • Measure the powder with a marked measuring spoon or cup and mix with food. 

  • Measure the oral liquid medicine with a marked measuring spoon, oral syringe, or medicine cup. The oral liquid may be mixed with food.

What to do if you miss a dose of Vitamin K2

  • It is generally not harmful if you miss a dose of a vitamin supplement. Take it as soon as you remember. Do not take two doses at one time.

Vitamin K2 contraindications - Who shouldn't take Vitamin K2?

  • You should not take vitamin K2 if you have had an allergic reaction to it as a single vitamin supplement or in a multivitamin.

Vitamin K2 warnings

  • Those with a rare metabolic condition called Glucose-6-phosphate dehydrogenase (G6PD) deficiency should avoid vitamin K2.

  • Too much vitamin K2 can be harmful to those with a kidney disease or receiving dialysis treatments.

  • Tell any doctor or dentist who treats you that you are taking vitamin K2. You may need to stop using this medicine several days before you have surgery or medical tests.

  • Ask your healthcare provider before using this medicine if you have heart disease, liver disease, kidney stones, an overactive thyroid gland, a bleeding disorder, or sarcoidosis. Tell your doctor if you smoke or drink alcohol regularly.

  • If you are pregnant or breastfeeding, ask your doctor what vitamins are best for you to use.

  • Do not take vitamin K if you are under 18 years old without the advice of a healthcare professional.

Vitamin K2 interactions & what to avoid when taking Vitamin K2

  • Do not take vitamin K2 if you are taking anticoagulants (blood thinners), such as warfarin, without the advice of a healthcare professional.

Vitamin K2 side effects - How does Vitamin K2 make you feel?

Vitamin K2 is normally well-tolerated. Less serious side effects may include:

  • Constipation or diarrhea

  • Loss of appetite or bad taste in your mouth

  • Nausea, heartburn, or upset stomach

The following more serious side effects should be discussed with your healthcare professional or may require immediate medical assistance:

  • Bloody diarrhea

  • Severe stomach pain or vomiting

  • Difficulty breathing

  • Muscle stiffness

  • Yellow eyes or skin

  • Difficulty swallowing

  • Fast or irregular breathing

  • Lightheadedness or fainting

  • Skin rash, hives, or itching

  • Swelling of eyelids, face, or lips

  • Tightness in chest

Sources:

Vitamin K2 News & Research

What vitamins should not be taken together?

Medically reviewed by Keith Gardner, R.Ph.
Registered Pharmacist

Keith Gardner, R.Ph., is a graduate of Southwestern Oklahoma State University School of Pharmacy. He has 10 years of community pharmacy experience followed by a 22-year career with a major pharmaceutical company in which he served as a medical information consultant. In that role, Gardner provided medical information to consumers and healthcare providers in numerous disease states. He currently resides in Monument, Colorado, with his wife and three dogs.

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