Drug Interaction Report

Arnica and Fondaparinux: Interaction Details

A pharmacist-reviewed analysis of the Arnica and Fondaparinux interaction: the documented clinical effects, severity rating, onset, mechanism, and management considerations, with cited references throughout.

AI-assisted, pharmacist-reviewed · Source data updated Aug 8, 2026 · Sources: FDA labeling, DDInter 2.0, cited literature

Fondaparinux

Arixtra
+

Arnica

No brand names on record
Dr. Brian Staiger, PharmD, BCPS
Medically reviewed by
Dr. Brian Staiger, PharmD, BCPS
Updated Aug 8, 2026
Editorial policy · Data sources
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Interaction severity
Minor
Usually limited clinical impact.
How we grade severity & evidence

Severity levels

  • Contraindicated: These should generally not be used together.
  • Major: Potentially serious — often needs a change or close monitoring.
  • Moderate: Can be significant — usually manageable with monitoring.
  • Minor: Usually limited clinical impact.

Evidence grades

  • Established: Well documented — supported by controlled studies or strong clinical data.
  • Probable: Good supporting evidence, though not definitively proven.
  • Suspected: Some evidence suggests this interaction, but it is not well established.
  • Possible: Limited or conflicting evidence; the interaction may occur.
  • Theoretical: Predicted from the drugs' pharmacology; not yet confirmed in people.

Ratings come from the documented interaction literature and are reviewed by a pharmacist. They describe the documented risk of the combination, not what will necessarily happen to you — your dose, timing, and health picture all matter.

Of 16 documented Arnica interactions, 16 are rated minor — including this one.
Onset
unspecified
Evidence
theoretical
Severity
Minor

What happens

Increased risk of bleeding

Interaction Deep Dive

Theoretically, arnica may potentiate the effect of anticoagulants3. Arnica contains the coumarin derivatives scopoletin and umbelliferone which may increase anticoagulant activity 1. Arnica inhibited platelet aggregation in vitro 2. Caution is advised.

Why it happens (mechanism)

Additive anticoagulant effects

Literature reports

1 report — tap to read

a) Two constituents from arnica, helenalin (H) and 11-alpha, 13-dihydrodelenalin (DH), dose-dependently inhibited human platelet function in vitro. Blood was collected from healthy donors who had not received anti-inflammatory drugs in the previous two weeks. H and DH inhibited platelet aggregation and thromboxane B2 formation at concentrations from 3 to 300 micromolar. H inhibited arachidonic acid-induced platelet aggregation but not thromboxane B2 formation. The platelet inhibition may occur through sulfhydryl group interactions, likely associated with reduced phospholipase A2 activity 2.

Common questions

Can I take Arnica and Fondaparinux together?

Increased risk of bleeding Always confirm with your pharmacist or prescriber before making any change.

How serious is the Arnica and Fondaparinux interaction?

It is rated minor. Usually limited clinical impact.

How quickly could this interaction happen?

The documented onset is "unspecified". The timing of this interaction is not well characterized.

How strong is the evidence for this interaction?

The evidence is graded "theoretical". Predicted from the drugs' pharmacology; not yet confirmed in people.

From our Q&A

Real reader questions about these medications, each personally answered by our pharmacist:

Questions for your pharmacist

  • Does my dose of Arnica or Fondaparinux need adjusting while I take them together?
  • What symptoms should prompt me to call you or my prescriber right away?
  • Does the timing of my doses matter for this combination?
  • Is there anything you'd monitor while I'm on both?

References (3)

  1. Newall CA, Anderson LA, & Phillipson JDNewall CA, Anderson LA, & Phillipson JD: Herbal Medicines: A Guide for Healthcare Professionals, The Pharmaceutical Press, London, England, 1996.
  2. Schroder H, Losche W, Strobach H, et al: Helenalin and 11-alpha, 13-dihydrohelenalin, two constituents from Arnica montana L. inhibit human platelet function via thiol-dependent pathways. Thromb Res 1990; 57:839-845.
  3. Ernst E: Possible interactions between synthetic and herbal medicinial products. Part I: a systematic review of the evidence. Perfusion 2000; 13:4-15.
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Fondaparinux

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All Fondaparinux interactions (204) Fondaparinux drug information
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Arnica

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All Arnica interactions (16)
Beyond drug–drug

These medications also interact with supplements

Prescription drugs aren't the whole picture — herbal and dietary supplements can interact with them too. From the evidence-graded Natural Medicines database:

Fondaparinux + Danshen Piracetam Aconite Allspice Aloe Alpha-lipoic Acid Andrographis Arnica + 194 more

major · moderate · minor — check everything you take with our drug–supplement interaction checker.

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This information is for education, not a substitute for professional medical advice. Do not start, stop, or change any medication without talking to your pharmacist or prescriber.