Drug & supplement interaction

Arnica + Hydroxyurea

Hydroxyurea brand names: Droxia, Hydrea, Siklos, Xromi.

No Known Interaction
Medically reviewed by · Updated July 2026 · Pair last verified Sep 13, 2026
The bottom line No known interaction

We found no known interaction between Arnica and Hydroxyurea in our sources. Absence of a documented interaction is not the same as proven safety, and does not guarantee one does not exist. Do not start, stop, or change a medication or supplement based on this page; confirm with your pharmacist or doctor first. Additionally, although there is no interaction, the two are separately associated with some of the same side effects, which would make a new symptom harder to attribute to one or the other.

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Interaction report

Arnica and Hydroxyurea

We checked these two against our interaction database. Here is what we found.

No Known Interaction Found

We did not find a documented interaction between Hydroxyurea and Arnica in our sources. This does not guarantee that the combination is completely free of risk — there is often limited research on supplements and herbal products, especially around drug interactions.

If you decide to take both, the practical routine is simple: add one new thing at a time and note the date you started it. If the combination is going to disagree with you, it usually shows in the first days to a couple of weeks — and a start date turns “I’ve been feeling off” into something a pharmacist can actually work with. Do not stop a prescribed medicine on your own.

Always talk with your pharmacist or doctor before making changes to your medications or supplements, particularly if you take several medications or have an ongoing health condition.

Arnica safety at a glance

Arnica overall Use caution Topical and homeopathic forms are generally well tolerated, but undiluted arnica should never be swallowed.
Pregnancy Likely Unsafe When used orally or topically; avoid using. Read the full pregnancy detail
Breastfeeding Likely Unsafe When used orally or topically; avoid using. Read the full breastfeeding detail

Pregnancy & breastfeeding ratings are from Natural Medicines (Therapeutic Research Center) — the full detail is in the Special populations card below. Safety guidance is general; always confirm with your pharmacist or doctor for your situation.

Still wondering about combining Hydroxyurea and Arnica? Ask Dr. Brian Staiger, PharmD, BCPS directly ›
How we checked

Why No Interaction Is Listed for Hydroxyurea

Interactions in our licensed database are recorded against drug classes, not just single drug names. Hydroxyurea is filed under 2 classifications — antineoplastics, oral drugs. Arnica has documented interactions with 1 drug class — the most serious being anticoagulant/antiplatelet drugs (moderate) — and none of Hydroxyurea’s classifications are among them.

Classification data comes from our licensed Natural Medicines dataset. A medication can belong to classes beyond those recorded there, so this describes how the check was run — it is not a safety guarantee.

Keep it in perspective

Arnica Does Interact With Other Medications

Arnica has 122 moderate known drug interactions in our database — Hydroxyurea isn’t one of them. If you take anything else, check it against the full list below.

Moderate 122 No known interaction 2,708 (incl. Hydroxyurea)
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.

What to actually watch for

No Interaction Found — But Data Suggests Arnica and Hydroxyurea May Share Several of the Same Side Effects

This is not an interaction. Neither one changes how your body handles the other, and nothing here says they react together. What our sources do show is that each has separately been linked to the effects below — so taking both can make those effects more likely to turn up, and harder to pin on one or the other if they do. One of them is worth acting on rather than waiting out — marked below.

  • Shortness of breath Worth acting on Additional detail

    Arnica

    “Orally, arnica is unsafe and can cause toxicity. When used in homeopathic amounts, arnica seem to be generally well tolerated. Topically, arnica also seems to be generally well tolerated.

    Most Common Adverse Effects:

    Orally: Bleeding, gastroenteritis, hypertension, muscle paralysis, nausea and vomiting, shortness of breath.

    Topically: Contact dermatitis and irritation.

    Serious Adverse Effects (Rare):

    Orally: Arrhythm…”

    Arnica · Natural Medicines adverse-effect record, reported in arrhythmia.

    Hydroxyurea

    Listed in the ADVERSE REACTIONS section of the FDA label for Hydroxyurea. Read the label on DailyMed ›

  • Dry skin Additional detail

    Arnica

    “Orally, arnica can cause irritation of mucous membranes (11,17113). Topically, arnica can cause contact itchiness, dry skin, and rash. Oral lesions resulted in a woman who used a mouthwash incorrectly by not following dilution instructions. The mouthwash was 70% alcohol and contained arnica and oil of peppermint.”

    Arnica · Natural Medicines adverse-effect record, reported in dry skin.

    3 sources cited
    1. 11. Leung AY, Foster S. Encyclopedia of Common Natural Ingredients Used in Food, Drugs and Cosmetics. 2nd ed. New York, NY: John Wiley & Sons, 1996.
    2. 17113. Adkison JD, Bauer DW, Chang T. The effect of topical arnica on muscle pain. Ann Pharmacother 2010;44:1579-84. PubMed
    3. 19106. Moghadam BK, Gier R, and Thurlow T. Extensive oral mucosal ulcerations caused by misuse of a commercial mouthwash. Cutis 1999;64:131-134.

    Hydroxyurea

    Listed in the ADVERSE REACTIONS section of the FDA label for Hydroxyurea. Read the label on DailyMed ›

  • Diarrhea / Stomach pain reported in 6.7% of FDA reports for Hydroxyurea Additional detail

    Arnica

    “Orally, arnica can cause stomach pain, nausea, vomiting, and diarrhea (11,17113,19101,19102). Homeopathic arnica has been reported to cause dry mouth (30C) and sore tongue (6C). A 24-year-old female presented to the emergency department with palpitations and vomiting 24 hours after ingesting a cup of tea that reportedly contained arnica flowers picked from her local area of mountainous Southern California.”

    Arnica · Natural Medicines adverse-effect record, reported in diarrhea.

    6 sources cited
    1. 11. Leung AY, Foster S. Encyclopedia of Common Natural Ingredients Used in Food, Drugs and Cosmetics. 2nd ed. New York, NY: John Wiley & Sons, 1996.
    2. 17113. Adkison JD, Bauer DW, Chang T. The effect of topical arnica on muscle pain. Ann Pharmacother 2010;44:1579-84. PubMed
    3. 19101. No authors listed. Final report on the safety assessment of Arnica montana extract and Arnica montana. Int.J.Toxicol. 2001;20:1-11. DOI
    4. 19102. Karow JH, Abt HP, Frohling M, and Ackermann H. Efficacy of Arnica montana D4 for healing of wounds after Hallux valgus surgery compared to diclofenac. J Altern Complement Med 2008;14:17-25.
    5. 19107. Stevinson C, Devaraj VS, Fountain-Barber A, et al. Homeopathic arnica for prevention of pain and bruising: randomized placebo-controlled trial in hand surgery. J R Soc Med 2003;96:60-65. PubMed
    6. 90610. Canders CP, Stanford SR, Chiem AT. A dangerous cup of tea. Wilderness Environ Med. 2014 Mar;25(1):111-2. PubMed

    Hydroxyurea

    Listed in the ADVERSE REACTIONS section of the FDA label for Hydroxyurea, and in voluntary FDA adverse-event reports. Read the label on DailyMed ›

  • Headache reported in 5.1% of FDA reports for Hydroxyurea Additional detail

    Arnica

    “Orally, arnica may cause drowsiness, nervousness, and headache (11, 17113, 19101, 19107).”

    Arnica · Natural Medicines adverse-effect record, reported in cluster headache.

    Hydroxyurea

    Listed in the ADVERSE REACTIONS section of the FDA label for Hydroxyurea, and in voluntary FDA adverse-event reports. Read the label on DailyMed ›

  • Nausea / Vomiting reported in 6.2% of FDA reports for Hydroxyurea Additional detail

    Arnica

    Recorded for Arnica in the same Natural Medicines adverse-effect record shown under Shortness of breath above.

    Hydroxyurea

    Listed in the ADVERSE REACTIONS section of the FDA label for Hydroxyurea, and in voluntary FDA adverse-event reports. Read the label on DailyMed ›

  • A skin rash Additional detail

    Arnica

    Recorded for Arnica in the same Natural Medicines adverse-effect record shown under Shortness of breath above.

    Hydroxyurea

    Listed in the ADVERSE REACTIONS section of the FDA label for Hydroxyurea. Read the label on DailyMed ›

Reported for Arnica but not commonly for Hydroxyurea: a fast or pounding heartbeat, raised blood pressure, anxiety or restlessness and loss of vision.

Effects for Hydroxyurea come from the ADVERSE REACTIONS section of its FDA label; effects for Arnica come from the Natural Medicines adverse-effect record, quoted above. Where a percentage is shown, it is the share of 21,027 voluntary FDA FAERS reports for Hydroxyurea that mention that effect — a reporting proportion, not an incidence rate and not evidence the drug caused it. Wording is matched across sources by our own clinical vocabulary, so treat this as a prompt to pay attention, not a diagnosis.

Special populations

Arnica in Pregnancy & Breastfeeding

Pregnancy And Lactation Likely Unsafe

When used orally or topically; avoid using.

DISCLAIMER: This tool is intended for informational purposes only, and should not be interpreted as specific medical advice. Patients should consult with a qualified healthcare provider before making decisions about therapies and/or health conditions.© 2026 Therapeutic Research Center

From our Q&A

Questions About Arnica or Hydroxyurea

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 Hydroxyurea, 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 Hydroxyurea

This page covers Arnica only. If you take other supplements — a multivitamin, a sleep aid, something for joints — the Hydroxyurea page lists 18 supplements it has a documented interaction with, worst first, each one explained.

The most serious there right now: Activated Charcoal (major), Coffee Charcoal (moderate), European Mandrake (moderate), Glucomannan (moderate) and Guar Gum (moderate).

By severity: 1 major · 7 moderate · 10 minor.

From our pharmacist’s overview on the Hydroxyurea page

“People take hydroxyurea (Droxia, Hydrea, Siklos, Xromi) for serious reasons, most often sickle cell disease or certain blood cancers, and it only works if a steady dose reaches the bloodstream. That is exactly what nearly all 18 supplements listed here can undermine, so this page earns real vigilance rather than a skim.”

Reviewed by 2 · Jul 18, 2026

Open the Hydroxyurea 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. Even though Arnica itself has no known interaction with Hydroxyurea, another ingredient on your label might. Find your product and we’ll check every ingredient on its label:

How much people look this up

Where Arnica and Hydroxyurea 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

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

29 days ago today
Medication Hydroxyurea
Top 5%

#40 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.

Where does our data come from?
  • Source: the Natural Medicines (TRC Healthcare) clinical database — the evidence-graded professional reference for herb & supplement interactions.
  • Citation library: 103,510 references behind our interaction content, 65,311 of them resolved to verified PubMed/DOI sources. See every Arnica reference on this page ↓
  • Freshness: we automatically re-check this combination every week — this pair was last verified September 13, 2026. The Arnica and Hydroxyurea records this page draws on were last updated July 10, 2026.
  • What “no known interaction” means: no documented interaction in the sources above — not a guarantee of safety. Supplements are studied far less than prescription drugs, so we say exactly what the evidence supports, and nothing more.
Data structure & sourcing designed and verified by .
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.

Arnica montana · Asteraceae · Flowers (and sometimes roots) · Topical creams, gels, ointments, oils, and homeopathic tablets or pellets

An interaction check asks whether these two react with each other — it does not ask whether Arnica is a good idea for someone in your situation. Here is what our Arnica record says about it on its own.

Arnica: dosing

There is no well-established standard dose for arnica. Topical products vary in strength, and homeopathic products are dosed according to the Homeopathic Pharmacopeia of the United States, which uses very high dilutions.The safest approach is to follow the directions on the product label and use it only as intended. Do not take undiluted arnica by mouth.

From our Arnica monograph — the full record covers uses, side effects and every documented interaction.

Read the full Arnica monograph & all interactions
Medication

About Hydroxyurea

What Is Hydroxyurea Used For?

Brand names: Droxia, Hydrea, Siklos, Xromi

Hydroxyurea is used for several serious conditions. Droxia, Siklos, and Xromi are each indicated to reduce the frequency of painful crises and reduce the need for blood transfusions in patients with sickle cell anemia who have recurrent moderate to severe painful crises. Siklos is approved for adults and children 2 years and older; Xromi is approved for children 6 months and older; Droxia is approved for adults.

Hydrea capsules and Hydroxyurea capsules are indicated for resistant chronic myeloid leukemia and for locally advanced squamous cell carcinomas of the head and neck (excluding the lip) when used together with chemoradiation.

Most-Reported Side Effects for Hydroxyurea

From FAERS, the FDA’s public side-effect reporting system (21,027 reports, all brands). Reports are voluntary and are not proof the drug caused the effect.

Fatigue 1,548 reports
Sickle cell anaemia with crisis 1,486 reports
Diarrhea 1,408 reports
Nausea 1,306 reports
Headache 1,068 reports
See full Hydroxyurea drug information
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
122Moderate
0Minor
2,707No known interaction
122 Moderate 2,707 No interaction
Moderate

122 interactions

Showing 60 of 122 moderate interactions — see all 122 on the Arnica page.

No interaction 2,707 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 2,707 medications checked with no known interaction — see the full Arnica list.

See the full Arnica interactions page
See every supplement checked against Hydroxyurea, ranked by severity
Evidence & sources

Arnica References

The 10 references that drive our Arnica monograph and interaction data, from the evidence-graded Natural Medicines (TRC Healthcare) database. Citations with a link open the study on PubMed or the publisher’s site.

  1. Leung AY, Foster S. Encyclopedia of Common Natural Ingredients Used in Food, Drugs and Cosmetics. 2nd ed. New York, NY: John Wiley & Sons, 1996.
  2. McGuffin M, Hobbs C, Upton R, Goldberg A, eds. American Herbal Products Association's Botanical Safety Handbook. Boca Raton, FL: CRC Press, LLC 1997.
  3. 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.
  4. Adkison JD, Bauer DW, Chang T. The effect of topical arnica on muscle pain. Ann Pharmacother 2010;44:1579-84. PubMed
  5. No authors listed. Final report on the safety assessment of Arnica montana extract and Arnica montana. Int.J.Toxicol. 2001;20:1-11. DOI
  6. Karow JH, Abt HP, Frohling M, and Ackermann H. Efficacy of Arnica montana D4 for healing of wounds after Hallux valgus surgery compared to diclofenac. J Altern Complement Med 2008;14:17-25.
  7. Venkatramani DV, Goel S, Ratra V, et al. Toxic optic neuropathy following ingestion of homeopathic medication Arnica-30. Cutan.Ocul.Toxicol. 2013;32:95-97. PubMed
  8. Moghadam BK, Gier R, and Thurlow T. Extensive oral mucosal ulcerations caused by misuse of a commercial mouthwash. Cutis 1999;64:131-134.
  9. Stevinson C, Devaraj VS, Fountain-Barber A, et al. Homeopathic arnica for prevention of pain and bruising: randomized placebo-controlled trial in hand surgery. J R Soc Med 2003;96:60-65. PubMed
  10. Canders CP, Stanford SR, Chiem AT. A dangerous cup of tea. Wilderness Environ Med. 2014 Mar;25(1):111-2. PubMed

Medication overviews come from MedlinePlus (NIH); supplement label data from the NIH Dietary Supplement Label Database. Content is written and reviewed by licensed HelloPharmacist pharmacists — see our data sources and editorial standards.

Pharmacist Counseling Corner

Taking Arnica and Hydroxyurea Together: Common Questions

Is it safe to take Arnica with Hydroxyurea?
We do not list a known interaction between Arnica and Hydroxyurea. That does not guarantee the combination is risk-free, so confirm with your pharmacist or doctor — especially if you take other medications or have a health condition.
Do Arnica and Hydroxyurea have any of the same side effects?
Yes — our sources link each of them separately to 8 of the same effects. That is not an interaction: neither changes how your body handles the other. It does mean that if one of those effects turns up, it can be harder to tell which one is behind it. They are listed on this page with the source behind each.
How was the Arnica and Hydroxyurea combination checked?
Interactions in our licensed database are recorded against drug classes. Hydroxyurea is filed under 2 classifications, and Arnica has documented interactions with 1 drug class — none of Hydroxyurea's classifications are among them. A medication can belong to classes beyond those recorded in our dataset, so this describes how the check was run rather than guaranteeing safety.
Does Arnica interact with any other medications?
Yes. Arnica has 122 documented drug interactions in our database — Hydroxyurea is simply not one of them. If you take anything else, it is worth checking each one; they are all listed on this page.
Does Hydroxyurea interact with any supplements?
Yes. Hydroxyurea has documented interactions with 18 supplements in our database — Arnica is not one of them. The Hydroxyurea interaction page linked on this page lists every one, ranked by severity.

Written and reviewed by the HelloPharmacist editorial staff. Our editorial policy

Where next

Keep Exploring

Arnica monograph Uses, safety profile, and every drug interaction in one place Hydroxyurea drug information The full plain-English guide to this medication Hydroxyurea supplement interactions Every supplement checked against Hydroxyurea, 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 References The 10 citations behind this page Ask a pharmacist Free, personal answer from our licensed team

Still Have a Question About Hydroxyurea 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.