Arnica

A herbal by Tabernaemontanus described arnica as a wound herb in 1613 ^{31Reference 31Committee on Herbal Medicinal Products · 2014Assessment report on Arnica montana L., flos (EMA/HMPC/198794/2012)View study →}. In the medieval period it was used for bruises and other injuries, varicose veins, phlebitis, gout, rheumatism, indigestion and heart disease ^{31Reference 31Committee on Herbal Medicinal Products · 2014Assessment report on Arnica montana L., flos (EMA/HMPC/198794/2012)View study →}. Early twentieth-century herbals give the tincture externally for sprains, bruises and chilblains on unbroken skin, and note that it was seldom taken internally because it irritates the stomach ^{27Reference 27A Modern Herbal · 2016A Modern Herbal. (n.d.). Arnica. Retrieved August 13, 2016, from http://www.botanical.com/botanical/mgmh/a/arnic058.htmlView study →}.

In Germany arnica has been used since 1957 for injuries such as bruises, sprains and haematomas, swelling after a fracture, rheumatic muscle and joint complaints, boils, insect-bite inflammation and superficial phlebitis ^{31Reference 31Committee on Herbal Medicinal Products · 2014Assessment report on Arnica montana L., flos (EMA/HMPC/198794/2012)View study →}. The German Commission E monograph of 1984 covered much the same list, and restricted arnica to external use ^{23,31Reference 23Blumenthal · 1998ReviewThe Complete German Commission E Monographs: Therapeutic Guide to Herbal Medicine — pharmacopoeial monograph (external use only)Reference 31Committee on Herbal Medicinal Products · 2014Assessment report on Arnica montana L., flos (EMA/HMPC/198794/2012)View study →}.

Commission E’s traditional preparations are the tincture diluted three- to tenfold for compresses, an infusion of 2 g in 100 mL, an oil of one part flowers to five parts fixed oil, and ointments containing 20–25% tincture, all for unbroken skin ^{23Reference 23Blumenthal · 1998ReviewThe Complete German Commission E Monographs: Therapeutic Guide to Herbal Medicine — pharmacopoeial monograph (external use only)}.

Homeopathic arnica is an ultra-dilution taken by mouth, not a herbal preparation. It is given for a wider list than the herbal tincture, above all bruising, soreness and swelling after surgery or childbirth ^{16,17Reference 16Ernst et al. · 1998Systematic reviewEfficacy of homeopathic arnica: a systematic review of placebo-controlled clinical trials — systematic reviewView study →Reference 17Hart et al. · 1997RCTDouble-blind, placebo-controlled, randomised clinical trial of homoeopathic arnica C30 for pain and infection after total abdominal hysterectomy — randomisedView study →}.

Placebo-controlled trials of the homeopathic preparation have largely found no effect ^{16,17,18Reference 16Ernst et al. · 1998Systematic reviewEfficacy of homeopathic arnica: a systematic review of placebo-controlled clinical trials — systematic reviewView study →Reference 17Hart et al. · 1997RCTDouble-blind, placebo-controlled, randomised clinical trial of homoeopathic arnica C30 for pain and infection after total abdominal hysterectomy — randomisedView study →Reference 18Tao et al. · 2022ReviewHomeopathic agents or vitamins in reducing ecchymosis after oculofacial surgery: a report by the American Academy of Ophthalmology — reviewView study →}.

A randomised, double-blind trial in 204 patients with radiologically confirmed hand osteoarthritis found an arnica tincture gel (50 g tincture per 100 g, DER 1:20) not inferior to 5% ibuprofen gel for pain and hand function over 21 days ^{1Reference 1Widrig et al. · 2007RCTChoosing between NSAID and arnica for topical treatment of hand osteoarthritis in a randomised, double-blind study — randomised, double-blindView study →}. Adverse events were similar (4.8% on arnica, 6.1% on ibuprofen) ^{1Reference 1Widrig et al. · 2007RCTChoosing between NSAID and arnica for topical treatment of hand osteoarthritis in a randomised, double-blind study — randomised, double-blindView study →}.

An open, multicentre study of a fresh-plant arnica gel, applied twice daily in 79 patients with mild to moderate knee osteoarthritis, reported significant improvements in WOMAC pain, stiffness and function scores at 3 and 6 weeks ^{2Reference 2Knuesel et al. · 2002Clinical trialArnica montana gel in osteoarthritis of the knee: an open, multicenter clinical trial — clinical trialView study →}. The local adverse-event rate was 7.6%, with one allergic reaction ^{2Reference 2Knuesel et al. · 2002Clinical trialArnica montana gel in osteoarthritis of the knee: an open, multicenter clinical trial — clinical trialView study →}.

One trial was an active-comparator non-inferiority study and the other was uncontrolled.

Gap: no placebo-controlled RCT of topical arnica in osteoarthritis exists, and the comparator in the one controlled trial was itself a topical gel.

The sesquiterpene lactone helenalin inhibits the transcription factor NF-κB. It does this not by blocking IκB degradation, as older models proposed, but by alkylating the p65 subunit directly ^{3Reference 3Lyss et al. · 1998In vitroThe anti-inflammatory sesquiterpene lactone helenalin inhibits the transcription factor NF-κB by directly targeting p65 — in vitroView study →}.

Arnica flower preparations suppress NF-κB and NF-AT activation and reduce croton-oil ear swelling in mice ^{4Reference 4Klaas et al. · 2002In vitroStudies on the anti-inflammatory activity of phytopharmaceuticals prepared from Arnica flowers — in vitro / animal model (mouse ear edema)View study →}. Their potency follows their sesquiterpene-lactone content, and the esters of dihydrohelenalin with unsaturated acids are more active than its acetate ^{4Reference 4Klaas et al. · 2002In vitroStudies on the anti-inflammatory activity of phytopharmaceuticals prepared from Arnica flowers — in vitro / animal model (mouse ear edema)View study →}. The lactones permeate the outer layer of the skin from tinctures and fresh-plant preparations, much more than the isolated compounds do ^{19Reference 19Wagner et al. · 2004In vitroSkin penetration studies of Arnica preparations and of their sesquiterpene lactones — in vitroView study →}.

The material varies. Spanish populations include both helenalin-rich and dihydrohelenalin-rich chemotypes ^{20Reference 20Perry et al. · 2009Sesquiterpene lactones in Arnica montana: helenalin and dihydrohelenalin chemotypes in SpainView study →}, and total lactone content rises as the flowers mature and is highest in the disc florets ^{21Reference 21Douglas et al. · 2004Sesquiterpene lactones in Arnica montana: a rapid analytical method and the effects of flower maturity and simulated mechanical harvesting on quality and yieldView study →}. A tincture of the helenalin chemotype inhibited NF-κB about twice as strongly as one of the dihydrohelenalin chemotype ^{29Reference 29Schmidt · 2023ReviewArnica montana L.: doesn’t origin matter? — reviewView study →}.

The human osteoarthritis and muscle-soreness results are the clinical read-out of this pathway. No human trial has measured an inflammatory biomarker.

Results are mixed, and concentration may be the reason.

A rater-blinded RCT using standardised pulsed-dye-laser bruises found a 20% arnica ointment, applied twice daily under occlusion for two weeks, improved bruising more than white petrolatum and more than a 1% vitamin K and retinol mix, though not more than 5% vitamin K ^{5Reference 5Leu et al. · 2010RCTAccelerated resolution of laser-induced bruising with topical 20% arnica: a rater-blinded randomised controlled trial — randomisedView study →}.

A double-blind, placebo-controlled trial of an arnica gel in 19 patients with post-laser facial bruising found no difference from its base ^{6Reference 6Alonso et al. · 2002RCTEffects of topical arnica gel on post-laser treatment bruises — randomised, placebo-controlledView study →}. A 2022 American Academy of Ophthalmology review found that in seven controlled studies, oral or topical arnica gave no or negligible benefit for bruising after eyelid, facial or laser surgery ^{18Reference 18Tao et al. · 2022ReviewHomeopathic agents or vitamins in reducing ecchymosis after oculofacial surgery: a report by the American Academy of Ophthalmology — reviewView study →}.

Gap: the positive result comes from a high-concentration (20%) topical. Lower-strength gels have failed, and no trial has standardised the preparation.

An ethanolic extract of arnica flowers, rich in phenolics and flavonoids, scavenged free radicals in DPPH, ORAC and Trolox-equivalent assays ^{7Reference 7Craciunescu et al. · 2012In vitroEvaluation of antioxidant and cytoprotective activities of Arnica montana L. and Artemisia absinthium L. ethanolic extracts — in vitroView study →}. In a mouse fibroblast (NCTC) cell line it protected cells against hydrogen-peroxide damage, best at 10 mg/L ^{7Reference 7Craciunescu et al. · 2012In vitroEvaluation of antioxidant and cytoprotective activities of Arnica montana L. and Artemisia absinthium L. ethanolic extracts — in vitroView study →}. The extract was rich in quercetin, rutin and apigenin ^{7Reference 7Craciunescu et al. · 2012In vitroEvaluation of antioxidant and cytoprotective activities of Arnica montana L. and Artemisia absinthium L. ethanolic extracts — in vitroView study →}.

This is a single cell line with no human outcome, and a wormwood (Artemisia absinthium) extract was more strongly antioxidant in the same assays ^{7Reference 7Craciunescu et al. · 2012In vitroEvaluation of antioxidant and cytoprotective activities of Arnica montana L. and Artemisia absinthium L. ethanolic extracts — in vitroView study →}.

A double-blind, randomised, placebo-controlled trial tested topical arnica in 20 well-trained men after a downhill run designed to cause delayed-onset muscle soreness, reapplied every 4 waking hours ^{8Reference 8Pumpa et al. · 2014RCTThe effects of topical Arnica on performance, pain and muscle damage after intense eccentric exercise — randomised, placebo-controlledView study →}. The arnica group reported less pain, on both a visual analogue scale and muscle tenderness, at 72 hours after exercise ^{8Reference 8Pumpa et al. · 2014RCTThe effects of topical Arnica on performance, pain and muscle damage after intense eccentric exercise — randomised, placebo-controlledView study →}.

Arnica changed no performance measure (peak torque, jump height) and no blood marker of muscle damage or inflammation (creatine kinase, myoglobin, IL-1β, IL-6, TNF-α, CRP) ^{8Reference 8Pumpa et al. · 2014RCTThe effects of topical Arnica on performance, pain and muscle damage after intense eccentric exercise — randomised, placebo-controlledView study →}.

A 10% w/v Arnica montana extract was tested by agar diffusion against 15 oral micro-organisms, alongside propolis ^{9Reference 9Koo et al. · 2000In vitroIn vitro antimicrobial activity of propolis and Arnica montana against oral pathogens — in vitroView study →}. The arnica extract showed no significant antimicrobial activity ^{9Reference 9Koo et al. · 2000In vitroIn vitro antimicrobial activity of propolis and Arnica montana against oral pathogens — in vitroView study →}. It slightly reduced the adherence of Streptococcus mutans (19%) and S. sobrinus (15%) and the formation of insoluble glucan (29%), where propolis inhibited all three strongly ^{9Reference 9Koo et al. · 2000In vitroIn vitro antimicrobial activity of propolis and Arnica montana against oral pathogens — in vitroView study →}.

Reviews list antibacterial and antifungal activity as a property of arnica extracts ^{13Reference 13Kriplani et al. · 2017ReviewArnica montana L. — a plant of healing: review — reviewView study →}. There is no infection model and no clinical antimicrobial use.

Purified helenalin induces apoptosis in leukaemia (Jurkat) T cells at 10–50 µM through caspase-3 and -8 activation. The effect does not depend on the CD95 death receptor and is not blocked by Bcl-2 or Bcl-xL overexpression ^{10Reference 10Dirsch et al. · 2001In vitroHelenalin triggers a CD95 death receptor-independent apoptosis that is not affected by overexpression of Bcl-xL or Bcl-2 — in vitroView study →}. Related sesquiterpene lactones share this property ^{11Reference 11Dirsch et al. · 2001In vitroCytotoxic sesquiterpene lactones mediate their death-inducing effect in leukemia T cells by triggering apoptosis — in vitroView study →}.

The same NF-κB p65 repression behind the anti-inflammatory action also triggers autophagic cell death in cancer cells ^{12Reference 12Lim et al. · 2012In vitroNF-κB p65 repression by the sesquiterpene lactone, helenalin, contributes to the induction of autophagy cell death — in vitroView study →}.

Helenalin is toxic taken internally, and arnica is used only on intact skin ^{22,23Reference 22Cosmetic Ingredient Review Expert Panel · 2001ReviewFinal report on the safety assessment of Arnica montana extract and Arnica montanaView study →Reference 23Blumenthal · 1998ReviewThe Complete German Commission E Monographs: Therapeutic Guide to Herbal Medicine — pharmacopoeial monograph (external use only)}.

Gap: cell-line only, at micromolar concentrations of an isolated toxic constituent. There is no whole-herb, animal or clinical anticancer evidence.

A methanolic extract of Arnica montana flower heads showed moderate anti-acetylcholinesterase activity in vitro, alongside antioxidant capacity ^{24Reference 24Zheleva-Dimitrova et al. · 2012In vitroAntioxidant and acetylcholinesterase inhibitory potential of Arnica montana cultivated in Bulgaria — in vitroView study →}. Cholinesterase inhibitors are used for the symptoms of Alzheimer’s disease.

Gap: one enzyme assay, with no animal or clinical follow-up.

Internal use. Arnica must not be taken by mouth. Swallowed arnica products have caused severe gastroenteritis, nervousness, a fast heart rate, muscle weakness and death ^{22Reference 22Cosmetic Ingredient Review Expert Panel · 2001ReviewFinal report on the safety assessment of Arnica montana extract and Arnica montanaView study →}. Heart-rhythm disturbance and organ damage have also been attributed to helenalin taken internally. Commission E and the EU monograph limit arnica to use on the skin ^{23,28,31Reference 23Blumenthal · 1998ReviewThe Complete German Commission E Monographs: Therapeutic Guide to Herbal Medicine — pharmacopoeial monograph (external use only)Reference 28Committee on Herbal Medicinal Products · 2014ReviewCommunity herbal monograph on Arnica montana L., flos (EMA/HMPC/198793/2012) — pharmacopoeial monographView study →Reference 31Committee on Herbal Medicinal Products · 2014Assessment report on Arnica montana L., flos (EMA/HMPC/198794/2012)View study →}.

Broken skin, eyes and mucous membranes. Arnica should not be used on broken skin ^{28Reference 28Committee on Herbal Medicinal Products · 2014ReviewCommunity herbal monograph on Arnica montana L., flos (EMA/HMPC/198793/2012) — pharmacopoeial monographView study →}. The EU monograph’s draft revision adds that it should not be applied near the eyes or mucous membranes, and that the tincture should be diluted before use ^{30Reference 30Committee on Herbal Medicinal Products · 2025ReviewEuropean Union herbal monograph on Arnica montana L., flos — draft revision 1 (EMA/HMPC/524586/2024)View study →}. The lactones pass into the outer layer of the skin from tinctures and gels ^{19Reference 19Wagner et al. · 2004In vitroSkin penetration studies of Arnica preparations and of their sesquiterpene lactones — in vitroView study →}.

Allergy. Arnica is contraindicated in people allergic to it or to other members of the daisy family (Asteraceae) ^{28Reference 28Committee on Herbal Medicinal Products · 2014ReviewCommunity herbal monograph on Arnica montana L., flos (EMA/HMPC/198793/2012) — pharmacopoeial monographView study →}. Allergic reactions such as itching, redness and eczema can occur ^{28Reference 28Committee on Herbal Medicinal Products · 2014ReviewCommunity herbal monograph on Arnica montana L., flos (EMA/HMPC/198793/2012) — pharmacopoeial monographView study →}. Allergic contact dermatitis is well known, but given how widely arnica is used, contact allergy is relatively uncommon ^{31Reference 31Committee on Herbal Medicinal Products · 2014Assessment report on Arnica montana L., flos (EMA/HMPC/198794/2012)View study →}. Prolonged or repeated use raises the risk ^{22Reference 22Cosmetic Ingredient Review Expert Panel · 2001ReviewFinal report on the safety assessment of Arnica montana extract and Arnica montanaView study →}.

Children. The 2014 EU monograph does not recommend arnica under 12 years of age for lack of data ^{28Reference 28Committee on Herbal Medicinal Products · 2014ReviewCommunity herbal monograph on Arnica montana L., flos (EMA/HMPC/198793/2012) — pharmacopoeial monographView study →}. The draft revision keeps this for some preparations and lowers it to 3 years for others ^{30Reference 30Committee on Herbal Medicinal Products · 2025ReviewEuropean Union herbal monograph on Arnica montana L., flos — draft revision 1 (EMA/HMPC/524586/2024)View study →}.

Duration. If symptoms worsen, or last longer than 3–4 days, a doctor or qualified practitioner should be consulted ^{28Reference 28Committee on Herbal Medicinal Products · 2014ReviewCommunity herbal monograph on Arnica montana L., flos (EMA/HMPC/198793/2012) — pharmacopoeial monographView study →}. For insect bites and boils, fever or a spreading skin infection is a reason to seek care, and boils on the face should be treated by a doctor ^{30Reference 30Committee on Herbal Medicinal Products · 2025ReviewEuropean Union herbal monograph on Arnica montana L., flos — draft revision 1 (EMA/HMPC/524586/2024)View study →}.

Interactions. None have been reported ^{28Reference 28Committee on Herbal Medicinal Products · 2014ReviewCommunity herbal monograph on Arnica montana L., flos (EMA/HMPC/198793/2012) — pharmacopoeial monographView study →}.

Homeopathic arnica. Homeopathic ultra-dilutions are a separate preparation and are not covered by these cautions.