Drug & supplement interaction

Spinach + Warfarin

Warfarin brand name: Warfarin.

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

Spinach has a moderate interaction with Warfarin. Spinach contains vitamin K, which can interfere with the activity of warfarin.

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

Spinach and Warfarin

Here is the interaction we found between these two, with the evidence behind it.

Moderate

WARFARIN (Coumadin)

Spinach contains vitamin K, which can interfere with the activity of warfarin.
In human research, although eating spinach with one meal does not result in coagulation test results outside the therapeutic range, daily consumption for one week necessitates dose adjustment of warfarin. Individuals using anticoagulants should consume a consistent daily amount of spinach to maintain the effect of anticoagulant therapy.
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 is the simple version: spinach is loaded with vitamin K, and vitamin K is the very thing your warfarin works against. Warfarin thins your blood by lowering your body's use of vitamin K to make clotting factors. So when you eat a lot of spinach, you are giving your body more of the ingredient warfarin is trying to hold down, which can make your warfarin less effective and nudge your INR lower. That could leave you at higher risk for a clot.

The good news is that consistency, not avoidance, is the key. You do not have to give up spinach. Just keep your weekly amount about the same rather than bingeing one week and skipping the next. Since warfarin is a finicky drug where small swings matter, let your doctor or pharmacist know if your diet changes a lot so your INR can be checked.

Contact Dr. Brian directly if you have additional questions on this interaction
References
  1. Brinker F. Herb Contraindications and Drug Interactions. 2nd ed. Sandy, OR: Eclectic Medical Publications, 1998.
  2. Karlson, B., Leijd, B., and Hellstrom, K. On the influence of vitamin K-rich vegetables and wine on the effectiveness of warfarin treatment. Acta Med Scand. 1986;220(4):347-350. 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

Spinach Also Interacts With Other Medications

Spinach has 87 moderate known drug interactions in our database — the Warfarin one above is one of them. If you take anything else, check it against the full list below.

Moderate 87 No known interaction 2,743 (incl. Warfarin)
Taking anything else?

Check Another of Your Medications Against Spinach

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

From our Q&A

Questions About Spinach or Warfarin

These are real questions from readers, answered by the pharmacists at HelloPharmacist — written by a person, not generated from a database. Each one covers Spinach or Warfarin, 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

This page covers Spinach only. If you take other supplements — a multivitamin, a sleep aid, something for joints — the Warfarin 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).

By severity: 16 major · 301 moderate · 44 minor.

From our pharmacist’s overview on the Warfarin page

“People take warfarin to prevent dangerous clots, and many are the same people reaching for glucosamine for sore joints or a multivitamin containing vitamin K, which makes this a list that deserves genuine respect. Of the 361 supplements on file for warfarin, 16 carry a major rating, and the danger runs in both directions: some add to w…”

Reviewed by 2 · Jul 18, 2026

Open the Warfarin interaction page

One more smart check

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

We hold 3,925 real supplement products containing Spinach, each one broken down to its full ingredient list — and combination products often carry several ingredients besides Spinach. Your product may carry other ingredients that interact with Warfarin too, on top of Spinach — 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 Spinach and Warfarin 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 Spinach
Top 10%

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

29 days ago today
Medication Warfarin
Top 10

#5 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 Spinach

What is Spinach?

  • General nutrition and antioxidant support
  • Eye health
  • Heart health and blood pressure
  • Athletic performance
  • Constipation and digestive support

Spinach is a nutrient-dense leafy green that is a healthy part of a balanced diet, providing vitamins, minerals, fiber, and antioxidants. While it is very safe as a food, concentrated supplements and extracts are far less studied, and most specific health claims are not strongly proven. People prone to kidney stones or taking blood thinners should be mindful of its oxalate and vitamin K content.

Read the full Spinach monograph & all interactions
Medication

About Warfarin

What Is Warfarin Used For?

Brand name: Warfarin

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 & Spinach

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

0Major
87Moderate
0Minor
2,742No known interaction
87 Moderate 2,742 No interaction
Moderate

87 interactions

Showing 60 of 87 moderate interactions — see all 87 on the Spinach page.

No interaction 2,742 drugs checked — show the list

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

Showing the 60 most looked-up of 2,742 medications checked with no known interaction — see the full Spinach list.

See the full Spinach interactions page
See every supplement checked against Warfarin, 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
Spinach monograph › Uses, safety, and every drug interaction in one place Warfarin supplement interactions › Every supplement checked against Warfarin, 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 Spinach and Warfarin Together: Common Questions

Can you take Spinach with Warfarin?
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.
How serious is the Spinach and Warfarin 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 and Spinach?

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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.