Quick answer

Ask your pharmacist or doctor before combining. NIH names one important exception to the rule that basic multivitamins rarely interact with medicines: medicine to reduce blood clotting, such as warfarin. People taking it should talk with their health care provider before taking any multivitamin with vitamin K, which lowers warfarin's effect.^1,2,3

Key facts

NIH says vitamin K decreases the effectiveness of warfarin, and that prescribers set the warfarin dose partly from the vitamin K a person routinely takes in.^1,2
Vitamin K is present in most multivitamin and mineral supplements, typically at less than 75% of the Daily Value.³
The warfarin label lists increased vitamin K intake among the factors that lower warfarin's effect and advises a consistent amount.⁴
Starting, stopping or switching a multivitamin changes the vitamin K you usually take in, which NIH says is part of how the dose is set.¹
NIH's vitamin E sheet says large doses of vitamin E taken with warfarin can raise the risk of bleeding.⁵

Ask your pharmacist or doctor first

Vitamin K counters warfarin, and the warfarin label lists more vitamin K in the diet among the factors that weaken its effect. NIH says people who take warfarin should talk with their health care provider before taking any multivitamin that contains vitamin K.^2,4

On the medicine's label

Why does NIH single out warfarin for multivitamins?

NIH's consumer fact sheet says basic multivitamins do not usually interact with medicines, with one important exception: medicine to reduce blood clotting, such as warfarin. It says to talk to your health care provider before taking any multivitamin or dietary supplement with vitamin K, because vitamin K lowers the drug's effectiveness and doctors base the dose partly on the amount of vitamin K you usually take in from food and supplements.¹

The sheet for health professionals makes the same point and adds that vitamin K is involved in blood clotting, which is why it works against warfarin.²

How much vitamin K is in a multivitamin?

NIH's vitamin K sheet for professionals says vitamin K is present in most multivitamin and mineral supplements, typically at less than 75% of the Daily Value. Products with vitamin K alone, or with a few other nutrients such as calcium, magnesium or vitamin D, vary much more, and some provide very high amounts.³

That spread is why the Supplement Facts panel matters more than the name on the bottle. Vitamin K may be listed as phylloquinone or phytonadione (vitamin K1) or as a menaquinone (vitamin K2). NIH's warning says vitamin K without limiting it to one form.^1,6

What does the warfarin label say about vitamin K and consistency?

The label describes warfarin as a vitamin K antagonist, meaning it works against vitamin K, and lists increased vitamin K intake among the factors that may lower the INR response. It tells prescribers to advise a normal, balanced diet with a consistent amount of vitamin K and to avoid drastic changes. MedlinePlus gives the same advice, asking for steady amounts of vitamin K foods from week to week.^4,7

The label's instruction about extra INR checks names other drugs and botanicals, not multivitamins. So a useful thing to ask the clinic that manages your warfarin is how it wants to hear about a change in your multivitamin.⁴

Does anything else in a multivitamin matter with warfarin?

NIH's vitamin E sheet says taking large doses of vitamin E with anticoagulant medicines such as warfarin can increase the risk of bleeding, especially with low vitamin K intake, and that the amounts needed to cause clinically significant effects are unknown. Check whether any product you take lists vitamin E and ask your pharmacist how to read it.⁵

Some multis are sold for a purpose such as energy, sport, immune function or eye health. These often add herbs or other ingredients such as green tea, coenzyme Q10 or probiotics, and some contain nutrients well above the Daily Value.^1,2

The warfarin label names co-enzyme Q10 among the botanicals that may decrease warfarin's effect, so a product that adds it, or herbs, deserves the same question. The sources checked do not address the other ingredients a multivitamin can contain, which is not a finding either way.⁴

What to ask your pharmacist about a multivitamin and warfarin

Does my multivitamin contain vitamin K, and in which form?
If I start, stop or switch a multivitamin, how should the clinic hear about it before my next INR?
Does my product also contain vitamin E, coenzyme Q10 or herbs?
Do my other supplements, such as a calcium and vitamin D combination, add more vitamin K?

Questions people ask

Can you take multivitamins with warfarin?

Ask your pharmacist or doctor first. NIH says to talk with your health care provider before taking any multivitamin or supplement with vitamin K, because vitamin K lowers warfarin's effect.¹

Is there a multivitamin and warfarin interaction?

Yes, through the vitamin K in the product. NIH calls it the one important exception to multivitamins rarely interacting with medicines, and the warfarin label lists increased vitamin K intake among the factors that lower its effect.^1,4

Can you take multivitamin with warfarin if it has no vitamin K?

The sources checked address vitamin K, and the vitamin E and co-enzyme Q10 points above. A product with none of these is not covered by a finding either way, so ask your pharmacist to read the whole panel.^1,4,5

What if I already take a multivitamin every day?

NIH says doctors base the warfarin dose partly on the vitamin K you usually take in from food and supplements, so a daily multivitamin is part of that baseline. Tell the clinic what you take and ask before changing it.¹

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Sources

This page is information, not medical advice. Talk to your doctor or pharmacist about your own situation.