Most supplement "side effects" articles are either scary or dismissive. Vitamin K2 is a case where the honest answer is mostly reassuring, with one major exception you really need to know about.
Written by Vita Globe Editorial Team | Reviewed against NIH guidance, U.S. Pharmacopeia review and peer-reviewed research
Does vitamin K2 have side effects?
For healthy adults, vitamin K2 has a strong safety record. The Food and Nutrition Board set no upper limit for vitamin K because no adverse effects from food or supplements have been reported[1]. A U.S. Pharmacopeia review concluded that MK-7 supplements aren't associated with any serious risk to health[2]. The major exception is a drug interaction: vitamin K can counteract warfarin[1][3].
Caveat: "No upper limit" doesn't mean unlimited doses are proven safe. It means no harm has been documented at the intakes studied so far.
Sources: NIH ODS · USP safety review, 2017 · Holbrook et al., 2005 · Verified 2026-09-27
In this article
What are the most common side effects of vitamin K2?
In the research, surprisingly few. Across the studies reviewed by the U.S. Pharmacopeia, MK-7 wasn't linked to serious adverse events[2]. A 2022 meta-analysis of 16 randomized trials of K2 in postmenopausal women also reported no significant adverse effects[4].
As with any supplement, some people may notice mild stomach upset. If something doesn't agree with you, stop and check with a healthcare provider.
In gummy form, the non-vitamin ingredients (such as sweeteners, gelling agents and flavors) matter too, so check the label if you have sensitivities.
Why is there no upper limit for vitamin K?
An Upper Limit (UL) is the highest daily intake unlikely to cause harm. For vitamin K, the Food and Nutrition Board didn't set one because of its low potential for toxicity[1].
That's different from vitamins A and D, which do have upper limits. It's also worth knowing that the official Adequate Intakes (90 mcg a day for women, 120 mcg for men) cover vitamin K in general. There's no separate recommended amount or upper limit for K2 specifically[1].
The honest summary
- K2 has a good safety record in healthy adults.
- No upper limit exists, but that reflects a lack of reported harm, not proof that any amount is fine.
- Stick with the label's suggested use.
What's the biggest risk with vitamin K2?
A drug interaction. Warfarin (Coumadin) is a blood thinner that works by blocking vitamin K's role in making clotting factors. Taking more vitamin K can make warfarin less effective[1][3].
MK-7 stays in the bloodstream much longer than K1, and in a study in people on an oral anticoagulant it counteracted the drug at lower doses than K1[5]. That's why even modest K2 doses matter for warfarin users.
If you take warfarin, don't start, stop or change a vitamin K supplement without talking to your doctor. Your provider may need to monitor your INR more closely[6]. We go deeper in vitamin K2 and blood thinners.
Can vitamin K2 interact with other medications?
The main ones to know about run the other way: some medications can lower your vitamin K status[1].
- Antibiotics can reduce vitamin K made by gut bacteria.
- Bile acid sequestrants (cholesterol drugs) can reduce vitamin K absorption.
- Orlistat (a weight-loss drug) reduces the absorption of fat-soluble vitamins.
If you take any of these long term, ask your provider whether your vitamin K status needs attention.
Who should avoid vitamin K2 or ask first?
- Anyone on warfarin or another vitamin K antagonist.
- People with a bleeding or clotting disorder.
- Anyone pregnant or nursing, or giving supplements to a child.
- People scheduled for surgery or managing a chronic condition.
Newer blood thinners work differently from warfarin, but it's still smart to run any supplement by your prescriber.
Our option
Vita Globe Vitamin K2 Gummies
If K2 is right for you, our Vitamin K2 Gummies keep it simple. They're raspberry-flavored, with a suggested use of 2 gummies once daily, and they're vegan-friendly, gluten-free and non-GMO, made without artificial colors or flavors. Like every Vita Globe product, they're tested by an independent third-party lab.
Frequently asked questions
Can vitamin K2 cause blood clots?
In healthy people, low-dose MK-7 didn't affect a laboratory measure of clotting (thrombin generation)[7]. There's no evidence it causes clots in healthy adults, but people with clotting disorders or on blood thinners should get medical advice.
Is it safe to take vitamin K2 long term?
Some trials have used daily MK-7 for as long as three years. A meta-analysis of 16 trials reported no significant adverse effects[4], and the U.S. Pharmacopeia found no serious risks from MK-7 supplements[2].
Can you take too much vitamin K2?
No upper limit has been set for vitamin K and no adverse effects from food or supplements have been reported[1]. Still, follow the label rather than stacking multiple K2 products.
Does vitamin K2 raise blood pressure?
We couldn't find evidence that K2 raises blood pressure. If you notice any change after starting a supplement, talk to your doctor.
Sources
- Office of Dietary Supplements, National Institutes of Health. Vitamin K: Fact Sheet for Health Professionals. Updated March 29, 2021. ods.od.nih.gov
- Marles RJ, Roe AL, Oketch-Rabah HA. US Pharmacopeial Convention safety evaluation of menaquinone-7, a form of vitamin K. Nutr Rev. 2017;75(7):553-578. doi:10.1093/nutrit/nux022
- Holbrook AM, Pereira JA, Labiris R, et al. Systematic overview of warfarin and its drug and food interactions. Arch Intern Med. 2005;165(10):1095-1106. doi:10.1001/archinte.165.10.1095
- Ma ML, Ma ZJ, He YL, et al. Efficacy of vitamin K2 in the prevention and treatment of postmenopausal osteoporosis: a systematic review and meta-analysis of randomized controlled trials. Front Public Health. 2022;10:979649. doi:10.3389/fpubh.2022.979649
- Schurgers LJ, Teunissen KJF, Hamulyák K, Knapen MHJ, Vik H, Vermeer C. Vitamin K-containing dietary supplements: comparison of synthetic vitamin K1 and natto-derived menaquinone-7. Blood. 2007;109(8):3279-3283. doi:10.1182/blood-2006-08-040709
- MedlinePlus Medical Encyclopedia. Taking warfarin. U.S. National Library of Medicine. Reviewed January 1, 2025. medlineplus.gov
- Theuwissen E, Cranenburg EC, Knapen MH, et al. Low-dose menaquinone-7 supplementation improved extra-hepatic vitamin K status, but had no effect on thrombin generation in healthy subjects. Br J Nutr. 2012;108(9):1652-1657. doi:10.1017/S0007114511007185
About the Vita Globe Editorial Team
The Vita Globe Editorial Team researches and writes our wellness content, working from peer-reviewed research, systematic reviews and guidance from bodies such as the NIH and the FDA. We cite our sources inline and update articles when the evidence changes.
These statements have not been evaluated by the Food and Drug Administration. This product is not intended to diagnose, treat, cure, or prevent any disease. This article is for informational purposes only and is not a substitute for medical advice. Talk to your healthcare provider before starting any new supplement, particularly if you are pregnant, nursing, taking medication, or caring for a child.
