K2 Side Effects: Overdose, Marcumar & More

Vitamin K2 has hardly any side effects, and none of the research we opened turned up a true overdose. One exception is hard and has no ifs or buts: if you take Marcumar, warfarin or another coumarin-type blood thinner, K2 is not something you start on your own.

For everyone else the answer is calmer. Here is what is documented, where the evidence runs out, who should ask first, and what can actually cause complaints when you combine K2 with vitamin D3.

What side effects does vitamin K2 really have?

Few. A comprehensive safety review of menaquinone-7 (MK-7), the K2 form in good supplements, reaches a clear conclusion: taken as a food supplement, MK-7 is not linked to serious health risks. The same paper went through animal toxicity data and the adverse events reported in people, and it ends without a warning.

What does that look like in everyday terms? In healthy adults, clotting values stayed unchanged after 30 days on 90 µg MK-7 a day. The activity of the clotting factors made in the liver did not move either. K2 does not thicken your blood. In healthy circumstances you do not need to worry about clots. In a trial with seven dose steps from 10 to 360 µg a day, thrombin generation was not affected either.

Isolated complaints such as stomach pressure or a queasy feeling come with almost any tablet. None of the papers we read gives a reliable frequency for MK-7. If you react easily, take the tablet with a meal. If you are allergic to soy, read the ingredient list first and ask the manufacturer if in doubt, because K2 is often made from fermented soybeans (natto). No drama, just care.

Can you overdose on vitamin K2?

For healthy adults we know of no case, and the amounts used in research sit far above what one tablet delivers. Women after menopause took 180 µg MK-7 every day for three years, which is nine times what our tablet delivers on average per day. Three years in a row. The goal was bone health. In another trial, healthy women took 375 µg a day for a year, on top of calcium and vitamin D. That is many times what our tablet delivers on average. Even so, these were healthy adults under supervision, not a free pass for every case.

That is not an invitation to take handfuls. The research measures that the activation of vitamin K-dependent proteins in the body goes up, not that everyone feels something. Choose the amount by your purpose. As soon as medication is involved, talk it through with your practice before you change anything in your routine.

In short: you do not need to fear the amount. You do need to fear the wrong combination with a drug.

Marcumar, warfarin, phenprocoumon: this is a stop sign

Coumarin-type blood thinners, which include Marcumar (phenprocoumon), warfarin and acenocoumarol, work by blocking the body's use of vitamin K, which makes K2 their direct opponent. Plain and simple. If you take both, you may weaken the drug. The INR value your practice uses to set the dose then drops, quietly, without you feeling a thing. Not a theory. It is why people on these drugs have always kept their vitamin K intake from food steady, meaning the cabbage, spinach and the like that should land on the plate in roughly the same amounts each week.

Two measurements show where the thresholds sit. With vitamin K1, only a daily intake of 150 µg measurably lowered the INR in healthy, stably anticoagulated people. For MK-7, the research group that compared the two warns that supplements giving 50 µg a day or more can interfere with the treatment in a clinically relevant way. The difference: MK-7 stays in the blood for a very long time. With regular intake it accumulates, and that is exactly why even small amounts act more steadily and for longer than K1.

The opposite happens too. In patients with strongly fluctuating values, a small fixed daily amount of vitamin K was given under supervision, and their values became steadier. So vitamin K is not forbidden. In this case the practice sets the amount, using measurements, and you do not do it by feel.

So for you: if you take Marcumar, warfarin or acenocoumarol, you never start or stop K2 without talking to your anticoagulation clinic or your family doctor. Starting and stopping both shift the INR. Small amounts count too, and so do combination products containing K2. Newer drugs such as apixaban or rivaroxaban act at a different point, and vitamin K is not their opponent. Even so, tell your practice or pharmacy what you take.

Who should ask first

• Coumarin-type blood thinners: see above, no exceptions.
• An upcoming operation: tell the team which supplements you take, including vitamin K.
• Regular medication in general: a quick question at the pharmacy for any prescription drug.
• Pregnancy and breastfeeding, children and teenagers: our high-dose depot is not suitable for them.
• Soy allergy: read the ingredient list and ask the manufacturer if in doubt.

And the D3 in the combination? Why complaints usually come from vitamin D

If the tub says D3 plus K2, the K2 part is usually not behind a complaint. Look at the vitamin D. Persistent nausea, unusual thirst or constipation are reasons to have calcium and your 25-OH-D blood level measured. K2 does not catch a high D3 intake; we make no such promise, and we know of no research showing it.

Your dose therefore follows your blood level, not the big number on the pack. Convert every label to a daily figure by dividing the dose by the rhythm, because only that daily value can be compared with what you already get from food, sun and other supplements. Our Vitamin D3 Depot + K2Pure® delivers 5,000 IU vitamin D3 (125 µg) and 100 µg K2 in one tablet you take only every 5th day. On average: 1,000 IU D3 and 20 µg K2 a day. You can read more about dose and blood level in our guide to vitamin D side effects.

How to take K2 safely

• With a meal. K2 is fat-soluble. Breakfast with cheese, nuts or a spoon of oil in your muesli is a good place for it.
• Always the same. Pick a rhythm and an amount and stick with it. Changing amounts are exactly what drugs with a vitamin K link like least.
• Add it up. K2 is in combination products, multivitamins and bone sets. Check what you take in total.
• Read the label. The form (MK-7), the amount in µg and the intake instructions belong on it.

Vitamin K contributes to the maintenance of normal bones and contributes to normal blood clotting. Vitamin D contributes to the normal absorption and utilisation of calcium and phosphorus and contributes to the maintenance of normal bones. That is why the two so often share a tablet.

What to look for in a K2 supplement

Clean form beats big number. On every tub we check four things. First, MK-7 rather than a vague "vitamin K2": if the form is not stated, you do not know what you are taking. Second, a named raw material, in our case K2Pure® with over 99 % all-trans. Third, the amount in µg, so you can fit it into your day. Fourth, lab testing, because with fat-soluble vitamins, which your body can store, you want to be sure the tablet contains what the tub says, and nothing else.

Finally, work out the supply. At one tablet every five days, a tub of 180 tablets lasts 900 days, and exactly that calculation makes the comparison between two tubs honest.

Matching Products from Scheunengut

Our Vitamin D3 Depot + K2Pure® is built as a depot: 5,000 IU (125 µg) vitamin D3 and 100 µg vitamin K2 as K2Pure® (MK-7, over 99 % all-trans) in a plant-based, vegan tablet, one every 5th day, 20 µg K2 a day on average. A tub of 180 tablets lasts 900 days, we have raw materials and every finished batch tested independently in the lab, and the tablet is made in Germany. Vitamin D contributes to the normal function of the immune system and to the maintenance of normal muscle function, vitamin K to the maintenance of normal bones and to normal blood clotting.

Important for you: the high-dose depot is not suitable for pregnant or breastfeeding women, children or teenagers, and with coumarin-type blood thinners it only comes into question after talking to your doctor. Scheunengut stands behind both statements: since 2012, without investors, with a focus on pure raw-material quality.

Frequently Asked Questions (FAQ)

What side effects does vitamin K2 have?

Few, and mostly harmless. Taken as a food supplement, MK-7 is not linked to serious risks according to a safety review. If you react easily, take the tablet with a meal. If you have allergies, check the ingredient list.

Can you overdose on vitamin K2?

We know of no case in healthy adults. In research, healthy women took up to 375 µg MK-7 a day for a year. Our tablet delivers 20 µg a day on average. The real danger is not the amount but the combination with coumarin-type blood thinners.

Can I take vitamin K2 with Marcumar?

Not on your own. Marcumar blocks vitamin K, K2 works against it and can shift the INR value. As little as 50 µg MK-7 a day can interfere with the treatment in a clinically relevant way. Talk to your anticoagulation clinic or family doctor first.

Does the warning also apply to warfarin and Eliquis?

For warfarin, phenprocoumon and acenocoumarol, yes, because they work through vitamin K. Newer drugs such as apixaban (Eliquis) or rivaroxaban act at a different point. Even so, tell your practice or pharmacy what you take.

Does vitamin K2 affect the risk of thrombosis?

In healthy adults, clotting values and thrombin generation stayed unchanged on MK-7, including at amounts up to 360 µg a day. If you take medication because of a thrombosis, clear K2 with your practice first anyway.

Does vitamin D3 plus K2 have more side effects than vitamin D alone?

From everything we have read, anything unusual is more likely to come from the vitamin D. If nausea or strong thirst persists, have calcium and 25-OH-D measured. Always set your D3 dose by your blood level.

Who should not take a high-dose D3-K2 tablet?

Pregnant and breastfeeding women, children and teenagers, as stated on our product page. People on coumarin-type blood thinners only after talking to their doctor. With other medication or conditions, clear it first.