Drug & supplement interaction

Niacinamide + Warfarin Sodium

Warfarin Sodium brand names: Coumadin, Panwarfin, Sofarin.

Moderate Interaction
Medically reviewed by · Updated September 2026
The bottom line Moderate

Warfarin Sodium falls into 2 drug categories that Niacinamide can interact with; the most serious is rated moderate. Theoretically, niacinamide may have additive effects when used with anticoagulant or antiplatelet drugs, especially in patients on hemodialysis.

Read the full interaction report
SeverityModerate
LikelihoodUnlikely
Interactions2
EvidenceD
What do Severity, Likelihood & Evidence mean?
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Interaction report

Niacinamide and Warfarin Sodium

These two interact in 2 distinct ways. Each one is explained separately below.

Why Are There 2 Interactions?

Niacinamide interacts with whole categories of medication. Warfarin Sodium falls into 2 of those categories, so it can interact with Niacinamide in 2 different ways. We’ve listed each one below — your overall risk is driven by the most serious of them (Moderate).

Moderate

ANTICOAGULANT/ANTIPLATELET DRUGS

1 of 2

Why this applies to Warfarin Sodium

Warfarin Sodium falls under ANTICOAGULANT/ANTIPLATELET DRUGS — the group Niacinamide interacts with.

Theoretically, niacinamide may have additive effects when used with anticoagulant or antiplatelet drugs, especially in patients on hemodialysis.
Several cases of thrombocytopenia have been reported for hemodialysis patients treated with niacinamide 1 gram daily. Hemodialysis patients receiving niacinamide had almost a three-fold higher risk of developing thrombocytopenia when compared with those receiving placebo.
Severity Moderate Likelihood Unlikely Evidence D

Interaction has been demonstrated in animal or in lab research but has been shown not to occur in humans..

Dr. Brian Staiger, PharmD, BCPS
Dr. Brian Staiger explains PharmD, Clinical Pharmacist

Here's the gist for warfarin and niacinamide. The concern isn't really about how warfarin is broken down. Instead, the worry is that high-dose niacinamide (around 1 gram a day) has occasionally lowered platelet counts in people on hemodialysis. Platelets help your blood clot, so dropping them while you're already on a blood thinner could, in theory, add up and raise your bleeding risk a bit. That might show up as easy bruising, nosebleeds, bleeding gums, or blood in the urine or stool.

Honestly, this is only an anecdotal, theoretical concern, mostly seen in dialysis patients taking concentrated doses. The usual small amounts in a multivitamin or skin cream are very unlikely to matter. Still, because warfarin is so finicky, please run any high-dose B3 supplement past your pharmacist or doctor first, and keep up with your regular INR checks.

Contact Dr. Brian directly if you have additional questions on this interaction
References
  1. Rottembourg JB, Launay-Vacher V, Massard J. Thrombocytopenia induced by nicotinamide in hemodialysis patients. Kidney Int. 2005;68(6):2911-2. PubMed
  2. Zhang Y, Ma T, Zhang P. Efficacy and safety of nicotinamide on phosphorus metabolism in hemodialysis patients: A systematic review and meta-analysis. Medicine (Baltimore). 2018;97(41):e12731. PubMed
Moderate

WARFARIN (Coumadin)

2 of 2
There is limited evidence that niacinamide may increase the anticoagulant effects of warfarin.
In a case report, a patient on warfarin developed an elevated international normalized ratio (INR) of 8.4 after taking niacinamide 500 mg twice daily for 10 days. The patient's INR was previously stable, ranging between 2 and 3, with no other changes to current medications or diet reported. The elevated INR returned to the therapeutic range after receiving vitamin K and discontinuing niacinamide.
Severity Moderate Likelihood Possible Evidence D

Interaction has been documented in animal or in lab research, or the interaction has been documented in humans but is limited to case reports or conflicting clinical research exists.

Dr. Brian Staiger, PharmD, BCPS
Dr. Brian Staiger explains PharmD, Clinical Pharmacist

Here's the gist: there's a single case report where someone on stable warfarin saw their INR jump to 8.4 after taking niacinamide 500 mg twice a day for about 10 days. A higher INR means the blood is thinner than intended, which raises the risk of bleeding, things like easy bruising, nosebleeds, bleeding gums, or more serious internal bleeding. Their numbers settled back down after stopping the niacinamide and getting vitamin K.

I want to be honest about the evidence here: this is anecdotal, just one report, so we can't say for sure it'll happen to you. But warfarin is a narrow-therapeutic-index drug, meaning small shifts matter a lot. If you'd like to use a niacinamide supplement, check with your doctor or pharmacist first so they can watch your INR. Small amounts in food or skin-care products are very unlikely to be a problem.

Contact Dr. Brian directly if you have additional questions on this interaction
References
  1. Markham DJ, Barbosa NS, Degesys CA. Elevated International Normalized Ratio After Initiation of Niacin and Niacinamide Chemoprophylaxis for Patients on Warfarin. Dermatol Surg 2024;50(7):690-692. PubMed

What These Ratings Mean

Every interaction above is graded three ways — here’s the key to each label.

Severity how clinically significant the interaction is
Major

Clinically significant. Avoid the combination, or use only under close professional supervision.

Moderate

Usually worth avoiding or managing — may need monitoring, a dose change, or timing apart.

Minor

Generally not serious. Be aware of it and mention it to your pharmacist.

Likelihood how strong the evidence is that the interaction actually happens in people
  • LikelyWell-controlled human studies have demonstrated the likely existence of this interaction.
  • ProbableInteraction has not been documented in well-controlled studies, however, the interaction has been demonstrated in some small human studies or in controlled animal studies in conjunction with multiple case reports.
  • PossibleInteraction has been documented in animal or in lab research, or the interaction has been documented in humans but is limited to case reports or conflicting clinical research exists.
  • UnlikelyInteraction has been demonstrated in animal or in lab research but has been shown not to occur in humans.
Evidence the quality of the studies behind the rating (graded A–D)
  • AHigh-quality meta-analysis (quantitative systematic review).
  • BCase-control study.
  • CConsensus.
  • DAnecdotal evidence.

These ratings are for information only. Never start, stop, or otherwise change your therapy before speaking with your provider.

Keep it in perspective

Niacinamide Also Interacts With Other Medications

Niacinamide has 123 moderate known drug interactions in our database — the Warfarin Sodium one above is among them. If you take anything else, check it against the full list below.

Moderate 123 No known interaction 2,707 (incl. Warfarin Sodium)
Taking anything else?

Check Another of Your Medications Against Niacinamide

Covers the 2,830 medications we’ve checked against Niacinamide. Pick one to open its full report.

From our Q&A

Questions About Niacinamide or Warfarin Sodium

These are real questions from readers, answered by the pharmacists at HelloPharmacist — written by a person, not generated from a database. Each one covers Niacinamide or Warfarin Sodium, not necessarily both, but if one is close to what you were about to ask it will usually go further than a database entry can:

Not quite your question? Ask our pharmacists directly — it is free, there is no account required, and answers usually come back within 24 hours.

Everything else you take

See Every Supplement That Interacts With Warfarin Sodium

This page covers Niacinamide only. If you take other supplements — a multivitamin, a sleep aid, something for joints — the Warfarin Sodium page lists 361 supplements it has a documented interaction with, worst first, each one explained.

The most serious there right now: Activated Charcoal (major), Alfalfa (major), American Ginseng (major), Beer (major) and Cannabis (major).

Open the Warfarin Sodium interaction page

One more smart check

Taking Niacinamide as Part of a Dietary Supplement Product? Check It for Interactions

We hold 552 real supplement products containing Niacinamide, each one broken down to its full ingredient list — and combination products often carry several ingredients besides Niacinamide. Your product may carry other ingredients that interact with Warfarin Sodium too, on top of Niacinamide — and those would not show on this page. Find your product and we’ll check every ingredient on its label:

How much people look this up

Where Niacinamide and Warfarin Sodium Sit Against Everything Else

Out of every supplement and medication people look up on HelloPharmacist, here is where these two land this week — and which way each has been moving.

Supplement Niacinamide
Top 25%

#301 of 1,452 supplements looked up here in the last 7 days

29 days ago today
Medication Warfarin Sodium
Top 1%

#18 of 2,830 medications looked up here in the last 7 days

29 days ago today

Position among everything looked up on this site, not a measure of how commonly either one is used or how important it is. A supplement can climb this list because of a news story. It counts every request to the page, automated ones included, and nothing here identifies anyone.

Supplement

About Niacinamide

What is Niacinamide?

  • Acne and skin health
  • Pellagra (niacin deficiency)
  • Anti-aging and skin tone
  • Rosacea
  • Protecting against certain skin cancers

Niacinamide (also called nicotinamide) is a form of vitamin B3 used in supplements and skin-care products. It is well established for preventing and treating vitamin B3 deficiency, and there is moderate evidence for some skin uses, but many popular claims are still being studied. It is generally well tolerated at usual doses, but high amounts should be discussed with your doctor or pharmacist.

Read the full Niacinamide monograph & all interactions
Medication

About Warfarin

What Is Warfarin Used For?

Brand names: Coumadin, Panwarfin, Sofarin

Warfarin sodium tablets and Jantoven tablets are both used to prevent and treat venous thrombosis (blood clots in the veins) and pulmonary embolism (a clot in the lungs). They are also used to prevent clot-related complications in people with atrial fibrillation (an irregular heart rhythm) or who have had a heart valve replaced.

In people who have had a heart attack, warfarin is used to reduce the risk of death, another heart attack, stroke, or other clotting events. It does not dissolve an existing clot, but it helps prevent the clot from growing and stops new dangerous clots from forming.

See full Warfarin drug information
Keep checking

Other Drugs & Niacinamide

Browse every other medication we’ve checked against Niacinamide — both the ones with a known interaction and the ones without. Select any drug for the full detail.

0Major
123Moderate
0Minor
2,706No known interaction
123 Moderate 2,706 No interaction
Moderate

123 interactions

Showing 60 of 123 moderate interactions — see all 123 on the Niacinamide page.

No interaction 2,706 drugs checked — show the list

We also checked Niacinamide against these medications and found no known interaction in our sources. Open any page to confirm.

Showing the 60 most looked-up of 2,706 medications checked with no known interaction — see the full Niacinamide list.

See the full Niacinamide interactions page
See every supplement checked against Warfarin Sodium, ranked by severity
Sources

Sources & How We Checked

Interaction details are evidence-graded and sourced from the Natural Medicines database. The medication overview comes from MedlinePlus.

Content is written and reviewed by licensed HelloPharmacist pharmacists. See our data sources and editorial standards for how this information is built and checked.

Parts of this content are provided by the Therapeutic Research Center, LLC.

DISCLAIMER: Currently this does not check for drug-drug interactions. This is not an all-inclusive comprehensive list of potential interactions and is for informational purposes only. Not all interactions are known or well-reported in the scientific literature, and new interactions are continually being reported. Input is needed from a qualified healthcare provider including a pharmacist before starting any therapy. Application of clinical judgment is necessary.

© 2021 Therapeutic Research Center, LLC

Keep exploring
Niacinamide monograph › Uses, safety, and every drug interaction in one place Warfarin Sodium supplement interactions › Every supplement checked against Warfarin Sodium, ranked by severity Warfarin drug information › The full plain-English guide to this medication Supplement interaction checker › Check any supplement or product against your medications Browse medications A–Z › Every drug we've checked against herbs & supplements Ask a pharmacist › Free, personal answer from our licensed team
Pharmacist Counseling Corner

Taking Niacinamide and Warfarin Sodium Together: Common Questions

Can you take Niacinamide with Warfarin Sodium?
There is a moderate interaction, so it may be acceptable with monitoring or timing changes — but check with your pharmacist first. Read the full details on this page and confirm with your pharmacist before combining them.
Why are there 2 interactions listed for Niacinamide and Warfarin Sodium?
Warfarin Sodium belongs to more than one drug category, and Niacinamide interacts with each of those categories a little differently. We list every one so nothing is missed — your overall risk is driven by the most serious of them.
How serious is the Niacinamide and Warfarin Sodium interaction?
We rate it Moderate. This combination may require monitoring, a dose adjustment, or separating the times you take each one. Consult your pharmacist before using them together.

Written and reviewed by the HelloPharmacist editorial staff. Our editorial policy

Still Have a Question About Warfarin Sodium and Niacinamide?

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This information is for education only and is not a substitute for professional medical advice. Always check with your pharmacist or doctor before starting, stopping, or combining supplements and medications.