Warfarin and supplements: 11 sourced interactions

Anticoagulant (vitamin K antagonist), also sold as Jantoven and Coumadin. Of these, 1 studied in people and 10 named by an FDA label or NIH page. Plus 1 predicted from how each works (not established). Plus 2 food and drink lines. Each links its source and the date it was checked.

From the Interaction Map Sources checked Oct 25, 2026

A combination missing here is not on our list; that does not mean it is safe together.

Warfarin with supplements

Most serious first. Open a row for the mechanism, the source's words and the date checked.

Educational only. Check with your pharmacist or prescriber before changing anything you take.

Moderate

12
St John's wortStudiedSt John's wort weakens warfarin

moderate · Studied in people (PubMed) · evidence B · Breakdown by liver enzymes

St John's wort induces the liver enzymes that clear warfarin, so less of each dose stays active.

To raise with your pharmacist or prescriberDo not start or stop St John's wort while on warfarin without your prescriber; INR checks are usually discussed around any change (inferred).

  • PMID 15089812 · Jiang X, Br J Clin Pharmacol 2004 · Randomized open-label three-way crossover trial (12 healthy men); erratum 2004 corrects R-warfarin clearance only
  • Checked Oct 23, 2026
Coenzyme Q10Label or NIHAn NIH page names this pair (platelets and bleeding).

moderate · Named by an FDA label or NIH page · Platelets and bleeding

In the source’s own words; rated moderate from that wording, not from a study of the pair.

“CoQ10 may interact with the anticoagulant (blood thinner) warfarin and the diabetes drug insulin, and it may not be compatible with some types of cancer treatment.”

CranberryLabel or NIHAn NIH page names this pair (platelets and bleeding).

moderate · Named by an FDA label or NIH page · Platelets and bleeding

In the source’s own words; rated moderate from that wording, not from a study of the pair.

“There is conflicting evidence about whether cranberry interacts with the anticoagulant (blood thinner) warfarin.”

EchinaceaLabel or NIHThe FDA label names this pair (breakdown by liver enzymes).

moderate · Named by an FDA label or NIH page · Breakdown by liver enzymes

In the source’s own words; rated moderate from that wording, not from a study of the pair.

“Some botanicals and foods can interact with JANTOVEN through CYP450 interactions (e.g., echinacea, grapefruit juice, ginkgo, goldenseal, St. John's wort).”

  • FDA drug label (DailyMed) · JANTOVEN (WARFARIN SODIUM) TABLET [UPSHER-SMITH LABORATORIES, LLC], section 7.5
  • Checked Oct 23, 2026
Fish oil (omega-3)Label or NIHAn NIH page names this pair (platelets and bleeding).

moderate · Named by an FDA label or NIH page · Platelets and bleeding

In the source’s own words; rated moderate from that wording, not from a study of the pair.

“Fish oil might prolong clotting times, as indicated by an elevated international normalized ratio (INR), when it is taken with warfarin”

“However, these package inserts also state that patients taking these products with anticoagulants should be monitored periodically for changes in INR.”

  • NIH Office of Dietary Supplements · Office of Dietary Supplements · Omega-3 Fatty Acids: Fact Sheet for Health Professionals, Interactions with Medications > Warfarin (Coumadin) and similar anticoagulants
  • Checked Oct 23, 2026
GarlicLabel or NIHThe FDA label names this pair (platelets and bleeding).

moderate · Named by an FDA label or NIH page · Platelets and bleeding

In the source’s own words; rated moderate from that wording, not from a study of the pair.

“Some botanicals may cause bleeding events when taken alone (e.g., garlic and Ginkgo biloba) and may have anticoagulant, antiplatelet, and/or fibrinolytic properties.”

“This is especially important if you are going to have surgery or if you take medicines, such as anticoagulants or aspirin, that may also affect bleeding.”

Ginkgo bilobaLabel or NIHThe FDA label names this pair (platelets and bleeding).

moderate · Named by an FDA label or NIH page · Platelets and bleeding

In the source’s own words; rated moderate from that wording, not from a study of the pair.

“Some botanicals may cause bleeding events when taken alone (e.g., garlic and Ginkgo biloba) and may have anticoagulant, antiplatelet, and/or fibrinolytic properties.”

“Some botanicals and foods can interact with JANTOVEN through CYP450 interactions (e.g., echinacea, grapefruit juice, ginkgo, goldenseal, St. John's wort).”

“Ginkgo may increase the risk of bleeding in people who are taking anticoagulant drugs, such as warfarin.”

“Several instances of excessive bleeding during therapy with ginkgo have been attributed to drug interactions with antiplatelet medications or anticoagulants.”

GoldensealLabel or NIHThe FDA label names this pair (breakdown by liver enzymes).

moderate · Named by an FDA label or NIH page · Breakdown by liver enzymes

In the source’s own words; rated moderate from that wording, not from a study of the pair.

“Some botanicals and foods can interact with JANTOVEN through CYP450 interactions (e.g., echinacea, grapefruit juice, ginkgo, goldenseal, St. John's wort).”

  • FDA drug label (DailyMed) · JANTOVEN (WARFARIN SODIUM) TABLET [UPSHER-SMITH LABORATORIES, LLC], section 7.5
  • Checked Oct 23, 2026
MelatoninLabel or NIHAn NIH page names this pair (cause not established).

moderate · Named by an FDA label or NIH page · Cause not established

In the source’s own words; rated moderate from that wording, not from a study of the pair.

“In particular, people with epilepsy and those taking blood thinner medications need to be under medical supervision when taking melatonin supplements.”

Vitamin ELabel or NIHAn NIH page names this pair (platelets and bleeding).

moderate · Named by an FDA label or NIH page · Platelets and bleeding

In the source’s own words; rated moderate from that wording, not from a study of the pair.

“Vitamin E supplements can interact with certain medications, including anticoagulants, antiplatelets, simvastatin, and niacin.”

“As a result, taking large doses of vitamin E with anticoagulant or antiplatelet medications, such as warfarin (Coumadin), can increase the risk of bleeding, especially in conjunction with low vitamin K intake.”

  • NIH Office of Dietary Supplements · Office of Dietary Supplements · Vitamin E, Interactions with Medications · Anticoagulant and antiplatelet medications
  • Checked Oct 25, 2026
Vitamin KLabel or NIHThe FDA label names this pair (clotting factors (vitamin K)).

moderate · Named by an FDA label or NIH page · Clotting factors (vitamin K)

In the source’s own words; rated moderate from that wording, not from a study of the pair.

“JANTOVEN has a narrow therapeutic range (index), and its action may be affected by factors such as other drugs and dietary vitamin K.”

“increased vitamin K intake or hereditary warfarin resistance.”

“The amount of vitamin K in food may affect therapy with JANTOVEN.”

“Advise patients taking JANTOVEN to eat a normal, balanced diet maintaining a consistent amount of vitamin K.”

“Vitamin K can interact with certain medications, such as warfarin and other anticoagulants.”

“Vitamin K can have a serious and potentially dangerous interaction with anticoagulants such as warfarin (Coumadin) as well as phenprocoumon, acenocoumarol, and tioclomarol, which are commonly used in some European countries [7,8].”

“People who are taking warfarin and similar anticoagulants need to maintain a consistent intake of vitamin K from food and supplements because sudden changes in vitamin K intakes can increase or decrease the anticoagulant effect [45].”

Asian ginsengPredictedBoth can affect clotting or platelets, so bleeding risk may add up.

moderate · Predicted from how each works, not established · Platelets and bleeding

Predicted from what each is known to do, not studied as a pair and not established.

Both can affect clotting or platelets, so bleeding risk may add up.

Warfarin with food and drink

Food and drink

2
CoffeeLabel or NIHThe FDA label names this pair (breakdown by liver enzymes).

moderate · Named by an FDA label or NIH page · Breakdown by liver enzymes

In the source’s own words; rated moderate from that wording, not from a study of the pair.

“CYP1A2 acyclovir, allopurinol, caffeine”

  • FDA drug label (DailyMed) · JANTOVEN (WARFARIN SODIUM) TABLET [UPSHER-SMITH LABORATORIES, LLC], section 7.2
  • Checked Oct 23, 2026
GrapefruitLabel or NIHThe FDA label names this pair (breakdown by liver enzymes).

moderate · Named by an FDA label or NIH page · Breakdown by liver enzymes

In the source’s own words; rated moderate from that wording, not from a study of the pair.

“Some botanicals and foods can interact with JANTOVEN through CYP450 interactions (e.g., echinacea, grapefruit juice, ginkgo, goldenseal, St. John's wort).”

  • FDA drug label (DailyMed) · JANTOVEN (WARFARIN SODIUM) TABLET [UPSHER-SMITH LABORATORIES, LLC], section 7.5
  • Checked Oct 23, 2026

How these lines are sourced

Three kinds of line

  • Studied in people (PubMed): PubMed records that were opened and read, graded A (several controlled studies, or a finding in the dosing guidance), B (at least one controlled human study) or C (case reports, observational data or mechanism only).
  • Named by an FDA label or NIH page: quoted word for word from that page. Its severity comes from the source’s wording, not from a study of the pair.
  • Predicted from how each works, not established: built from sourced facts about each substance, such as the FDA’s table of enzyme roles. Never rated major.

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