Drug & supplement interaction

Caffeine + Warfarin

Warfarin brand name: Warfarin.

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

Caffeine has a moderate interaction with Warfarin. Theoretically, caffeine may increase the risk of bleeding if used with anticoagulant or antiplatelet drugs.

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

Caffeine and Warfarin

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

Moderate

ANTICOAGULANT/ANTIPLATELET DRUGS

Why this applies to Warfarin

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

Theoretically, caffeine may increase the risk of bleeding if used with anticoagulant or antiplatelet drugs.
Caffeine is reported to have antiplatelet activity. Theoretically, it might increase the risk of bleeding when used concomitantly with these agents; however, this interaction has not been reported in humans.
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 honest picture: warfarin is a blood thinner that lowers your blood's ability to clot, and it's a very dose-sensitive drug, so even small shifts can matter. Lab studies suggest caffeine may have a mild effect on platelets, which could in theory add to warfarin's clot-fighting action and slightly raise the chance of bruising or bleeding. The key word is theoretical, though. This has not actually been reported in people, and the evidence comes only from test-tube or animal work.

For most coffee or tea drinkers, a steady, moderate caffeine habit is unlikely to throw off your warfarin. The bigger concern would be high-dose caffeine supplements or energy products. If you notice easy bruising, nosebleeds, or pink urine, check in with your pharmacist or doctor before changing anything.

Contact Dr. Brian directly if you have additional questions on this interaction
References
  1. Ali M, Afzal M. A potent inhibitor of thrombin stimulated platelet thromboxane formation from unprocessed tea. Prostaglandins Leukot Med 1987;27:9-13. PubMed
  2. Ardlie NG, Glew G, Schultz BG, Schwartz CJ. Inhibition and reversal of platelet aggregation by methyl xanthines. Thromb Diath Haemorrh 1967;18:670-3. DOI

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

Caffeine Also Interacts With Other Medications

Caffeine has 8 major, 482 moderate, 164 minor 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.

Major 8 Moderate 482 Minor 164 No known interaction 2,176 (incl. Warfarin)
Taking anything else?

Check Another of Your Medications Against Caffeine

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

From our Q&A

Questions About Caffeine 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 Caffeine 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 Caffeine 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 Caffeine as Part of a Dietary Supplement Product? Check It for Interactions

We hold 6,775 real supplement products containing Caffeine, each one broken down to its full ingredient list — and combination products often carry several ingredients besides Caffeine. Your product may carry other ingredients that interact with Warfarin too, on top of Caffeine — 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 Caffeine 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 Caffeine
Top 5%

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

29 days ago today
Medication Warfarin
Top 10

#4 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 Caffeine

What is Caffeine?

  • Mental alertness and reducing fatigue
  • Improving athletic performance
  • Headache and migraine relief
  • Boosting focus and concentration
  • Weight loss aid

Caffeine is a natural stimulant found in coffee, tea, and many other plants and products. In moderate amounts it can boost alertness and reduce tiredness for most healthy adults, but too much can cause jitteriness, a racing heart, and sleep problems. Pregnant women and people with heart conditions or anxiety should be especially careful and check with a doctor or pharmacist.

Read the full Caffeine 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 & Caffeine

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

8Major
482Moderate
164Minor
2,175No known interaction
8 Major 482 Moderate 164 Minor 2,175 No interaction
Major

8 interactions

Moderate

482 interactions

Showing 60 of 482 moderate interactions — see all 482 on the Caffeine page.

Minor

164 interactions

Showing 60 of 164 minor interactions — see all 164 on the Caffeine page.

No interaction 2,175 drugs checked — show the list

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

Showing the 60 most looked-up of 2,175 medications checked with no known interaction — see the full Caffeine list.

See the full Caffeine 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
Caffeine 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 Caffeine and Warfarin Together: Common Questions

Can you take Caffeine 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 Caffeine 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 Caffeine?

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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.