Drug & supplement interaction

Arnica + Lepirudin

Lepirudin brand name: Refludan.

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

Arnica has a moderate interaction with Lepirudin. Theoretically, arnica might have additive effects with anticoagulant and antiplatelet drugs.

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

Arnica and Lepirudin

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

Moderate

ANTICOAGULANT/ANTIPLATELET DRUGS

Why this applies to Lepirudin

Lepirudin falls under ANTICOAGULANT/ANTIPLATELET DRUGS — the group Arnica interacts with.

Theoretically, arnica might have additive effects with anticoagulant and antiplatelet drugs. Homeopathic arnica preparations are unlikely to have this interaction.
In vitro evidence shows that sesquiterpene lactones in arnica flowers can decrease platelet aggregation. However, this effect has not been reported in humans.
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

Lepirudin (Refludan) is a powerful blood thinner given through an IV, usually in the hospital, to stop clots from forming. Arnica, in lab and animal studies, seems to make platelets (the cells that help blood clot) a little less sticky. Put those two together, and the worry is purely theoretical: in principle, arnica could add to the blood-thinning effect and slightly raise the chance of bruising or bleeding.

Here's the reassuring part. This has only been seen in test tubes, not in real people, and it's rated unlikely. Homeopathic arnica (the very diluted kind) almost certainly won't matter. Still, since lepirudin is already a strong anticoagulant, please let your hospital team or pharmacist know about any arnica you use.

Contact Dr. Brian directly if you have additional questions on this interaction
References
  1. 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;57:839-45.

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

Arnica Also Interacts With Other Medications

Arnica has 121 moderate known drug interactions in our database — the Lepirudin one above is one of them. If you take anything else, check it against the full list below.

Moderate 121 No known interaction 2,709 (incl. Lepirudin)
Taking anything else?

Check Another of Your Medications Against Arnica

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

From our Q&A

Questions About Arnica or Lepirudin

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

This page covers Arnica only. If you take other supplements — a multivitamin, a sleep aid, something for joints — the Lepirudin page lists 218 supplements it has a documented interaction with, worst first, each one explained.

The most serious there right now: Activated Charcoal (major), Danshen (major), Piracetam (major), Aconite (moderate) and Allspice (moderate).

By severity: 3 major · 190 moderate · 25 minor.

From our pharmacist’s overview on the Lepirudin page

“Lepirudin (Refludan) is a potent injectable blood thinner, typically given when heparin has caused a dangerous platelet reaction, and that makes this a list to read with real care. Of the 218 supplements and herbs with interactions on file, 202 can slow clotting on their own, piling extra bleeding risk onto a drug whose chief hazard is…”

Reviewed by 2 · Jul 18, 2026

Open the Lepirudin interaction page

One more smart check

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

We hold 43 real supplement products containing Arnica, each one broken down to its full ingredient list — and combination products often carry several ingredients besides Arnica. Your product may carry other ingredients that interact with Lepirudin too, on top of Arnica — 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 Arnica and Lepirudin 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 Arnica
Top half

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

29 days ago today
Medication Lepirudin
Steady interest

#2,641 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 Arnica

What is Arnica?

Arnica
  • Bruising
  • Muscle soreness
  • Joint pain (osteoarthritis)
  • Swelling after injury or surgery
  • Sprains and minor aches

Arnica is a daisy-family plant used mainly in topical and homeopathic products for bruising, muscle soreness, and pain. The evidence is mixed and mostly weak, and undiluted arnica taken by mouth can be toxic, so it should only be used on unbroken skin or in heavily diluted homeopathic forms. Talk to your pharmacist or doctor before using it.

Read the full Arnica monograph & all interactions
Keep checking

Other Drugs & Arnica

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

0Major
121Moderate
0Minor
2,708No known interaction
121 Moderate 2,708 No interaction
Moderate

121 interactions

Showing 60 of 121 moderate interactions — see all 121 on the Arnica page.

No interaction 2,708 drugs checked — show the list

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

Showing the 60 most looked-up of 2,708 medications checked with no known interaction — see the full Arnica list.

See the full Arnica interactions page
See every supplement checked against Lepirudin, 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
Arnica monograph › Uses, safety, and every drug interaction in one place Lepirudin supplement interactions › Every supplement checked against Lepirudin, ranked by severity 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 Arnica and Lepirudin Together: Common Questions

Can you take Arnica with Lepirudin?
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 Arnica and Lepirudin 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 Lepirudin and Arnica?

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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.