Health Care Professional Information

Scientific Name
Arnica montana
Common Name

Mountain tobacco, leopard’s bane, wolf’s bane, mountain arnica

Clinical Summary

Arnica is a perennial herb found in East Asia, Europe, the northern United States, and Canada. Its medicinal history dates back several centuries and arnica continues to be popular today. Its flowers and roots have been used to treat bruises, sprains, arthritic pain, and muscle aches. A highly diluted form of Arnica is also used in homeopathic remedies.

In vitro studies show that arnica has antimicrobial (1) and anti-inflammatory (2) properties. A few clinical trials suggest that topical arnica is helpful for osteoarthritis (3) (4) (5) and significantly reduces bruising compared with placebo or low-concentration vitamin K ointments (6). However, a small study reported that topical arnica actually increased pain 24 hours after calf exercises (7).

A systematic review of homeopathic arnica studies has previously considered their evidence of effectiveness to be insufficient (8). More recent studies report reduced postoperative swelling in patients following knee surgery (9), and reduced pain following tonsillectomy (10). Rigorous research is needed to determine the clinical benefits of homeopathic arnica.

Purported Uses
  • Bruises
  • Fevers
  • Inflammation
  • Osteoarthritis
  • Pain
  • Skin disorders
  • Sprains
Constituents
  • Flavonoid glycosides
  • Sesquiterpene lactones: helenalin and 11 alpha,13-dihydrohelenalin
  • Polysaccharides
  • Polyacetylenes
  • Tannins
  • Volatile oils
    (2) (11) (12) (13)
Mechanism of Action

Sesquiterpene lactones in arnica have anti-inflammatory properties and inhibit binding of transcription factors AP-1 and NF-κB to DNA (14). Using a tincture prepared from arnica flowers, this led to suppressed collagenase-1 (MMP1) and interstitial collagenase-13 (MMP13) mRNA levels in human articular chondrocytes in vitro (14). MMP13 and MMP1 enzymes are thought to play a significant role in cartilage and joint destruction and inflammation seen in osteoarthritis and rheumatoid arthritis. Both arnica tinctures and sesquiterpene lactones were found to suppress NF-κB activation and IL-12 production in dendritic cells at high concentrations, but can also have immunostimulatory effects when diluted (2). Another study found that sesquiterpene lactones inhibit platelet function by interacting with platelet sulfhydryl groups, probably associated with reduced phospholipase A2 activity (12). In addition to sesquiterpene lactones, the allergenic potential of arnica may be partly due to other allergens such as polyacetylenes (15).

Warnings

Oral intake of arnica-containing products can result in serious side effects. The FDA has classified pure arnica as an unsafe herb (16) and there are associated adverse effects with its use (see below) (11).

Contraindications

Surgical procedures: Avoid perioperatively due to antiplatelet effects demonstrated in vitro (12).
Open cuts, wounds, broken skin, mucous membranes: Topical arnica should be avoided on these areas.
Pregnant and nursing women: Ingestion of arnica tea by a nursing mother caused serious side effects in a newborn (17).
Allergies to sunflowers, marigolds, or ragweed: Individuals with allergies to members of the Asteracea family may likely be allergic to arnica.

Adverse Reactions

The FDA has classified pure arnica as an unsafe herb (16), and its oral intake has resulted in serious side effects. Topical and homeopathic arnica are generally considered safe, although one report describes an overdose with homeopathic arnica (see below).

Case reports
Oral, raw herb: Gastrointestinal distress, internal bleeding, tachycardia, dyspnea, and coma (11).
Oral, homeopathic overdose: Severe vomiting followed by acute, bilateral vision loss after accidental overdose (18).
Oral, infant exposure through breast-milk: Hemolytic anemia in a 9-day-old breastfed infant 48 hours after his mother began drinking an arnica flower tea (17).
Topical: Contact dermatitis (8).

Herb-Drug Interactions

Antiplatelet agents: Arnica inhibits platelet aggregation in vitro (12).
Warfarin or other anticoagulants: Arnica may potentiate their effects (19).

Literature Summary and Critique

Adkison JD, et al. The effect of topical arnica on muscle pain. Ann Pharmacother. 2010;44:1579-1584.
A total of 53 subjects were enrolled in this randomized, double-blind, placebo-controlled trial to evaluate whether topical Arnica montana cream could decrease subjective leg pain after a prescribed calf-raise exercise. Each patient received two tubes of cream: one containing arnica and the other containing placebo. The creams were applied to the right or left calf (as directed on tubes labels) immediately after exercise, and again 24 and 48 hours post-exercise. Subjects used an analog scale to rate pain severity at baseline, and 24, 48, and 72 hours after exercising. At 48 hours post-exercise, ankle range of motion and muscle tenderness were also measured. There were no significant differences in pain scores for the legs treated with the arnica or placebo creams at baseline. However, 24 hours post-exercise, pain scores for the arnica-treated legs were significantly higher than placebo (P<.005). Pain scores for the arnica and placebo creams were not significantly different at 48 and 72 hours post-exercise. No significant differences in ankle range of motion or muscle tenderness were detected for the two treatments.

Leu S, et al. Accelerated resolution of laser-induced bruising with topical 20% arnica: a rater-blinded randomized controlled trial. Br J Dermatol. 2010;163:557-563.
This double-blind, randomized, controlled study investigated the effect of a topical arnica formula on the resolution of skin bruising. The study enrolled 16 patients who then had two bruises created on each bilateral upper inner arm by a pulsed dye laser. One of 4 topical agents (5% vitamin K, 1% vitamin K/0.3% retinol, arnica, or white petrolatum) was randomly assigned to treat one of the 4 bruises. Each treatment was applied to the assigned bruise twice daily under occlusion for 2 weeks. A dermatologist rated the severity of the bruises at baseline and after 2 weeks of treatment. Improvement in bruise severity score was found to be significantly greater for arnica than for white petrolatum (P=.003) or 1% vitamin K/0.3 retinol (P=.01). Bruise reduction was also found to be nominally better with arnica than with 5% vitamin K, but the difference was not statistically significant. Investigators concluded that topical arnica ointment may reduce bruising more effectively than placebo or low-concentration vitamin K formulations.

Ross SM. Osteoarthritis: a proprietary Arnica gel is found to be as effective as ibuprofen gel in osteoarthritis of the hands. Holist Nurs Pract. 2008;22:237-239.
This randomized, double-blind, controlled, multicenter study enrolled 204 outpatients with osteoarthritis of the interphalangeal joints. Patients were randomized to receive 5% topical ibuprofen or arnica gel 3 times daily for 3 weeks. Patients were also allocated a preset number of acetaminophen tablets to be used as “rescue treatment” if the pain was unbearable. Study results indicated that the arnica gel was comparable to ibuprofen gel with respect to hand functional capacity, pain intensity, number of painful joints, duration and severity of morning stiffness, and acetaminophen consumption. The researchers concluded that arnica gel can be used as an alternative to ibuprofen gel in patients with osteoarthritis of the hand.

Dosage (Inside MSKCC Only)
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References
  1. Iauk L, Lo Bue AM, Milazzo I, et al. Antibacterial activity of medicinal plant extracts against periodontopathic bacteria. Phytother Res. Jun 2003;17(6):599-604.
  2. Lass C, Vocanson M, Wagner S, et al. Anti-inflammatory and immune-regulatory mechanisms prevent contact hypersensitivity to Arnica montana L. Exp Dermatol. Oct 2008;17(10):849-857.
  3. Knuesel O, Weber M, Suter A. Arnica montana gel in osteoarthritis of the knee: an open, multicenter clinical trial. Adv Ther. Sep-Oct 2002;19(5):209-218.
  4. Widrig R, Suter A, Saller R, et al. Choosing between NSAID and arnica for topical treatment of hand osteoarthritis in a randomised, double-blind study. Rheumatol Int. Apr 2007;27(6):585-591.
  5. Ross SM. Osteoarthritis: a proprietary Arnica gel is found to be as effective as ibuprofen gel in osteoarthritis of the hands. Holist Nurs Pract. Jul-Aug 2008;22(4):237-239.
  6. Leu S, Havey J, White LE, et al. Accelerated resolution of laser-induced bruising with topical 20% arnica: a rater-blinded randomized controlled trial. Br J Dermatol. Sep 2010;163(3):557-563.
  7. Adkison JD, Bauer DW, Chang T. The effect of topical arnica on muscle pain. Ann Pharmacother. Oct 2010;44(10):1579-1584.
  8. Ernst E, Pittler MH. Efficacy of homeopathic arnica: a systematic review of placebo-controlled clinical trials. Arch Surg. Nov 1998;133(11):1187-1190.
  9. Brinkhaus B, Wilkens JM, Ludtke R, et al. Homeopathic arnica therapy in patients receiving knee surgery: results of three randomised double-blind trials. Complement Ther Med. Dec 2006;14(4):237-246.
  10. Robertson A, Suryanarayanan R, Banerjee A. Homeopathic Arnica montana for post-tonsillectomy analgesia: a randomised placebo control trial. Homeopathy. Jan 2007;96(1):17-21.
  11. Dinman S. Arnica. Plast Surg Nurs. Jan-Mar 2007;27(1):52-53.
  12. 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. Mar 15 1990;57(6):839-845.
  13. Schulte KE, Rucker G. [Polyacetylenes and some other new contents of Arnica blossoms]. Arch Pharm Ber Dtsch Pharm Ges. May 1966;299(5):468-480.
  14. Jager C, Hrenn A, Zwingmann J, et al. Phytomedicines prepared from Arnica flowers inhibit the transcription factors AP-1 and NF-kappaB and modulate the activity of MMP1 and MMP13 in human and bovine chondrocytes. Planta Med. Oct 2009;75(12):1319-1325.
  15. Salapovic H, Geier J, Reznicek G. Quantification of Sesquiterpene Lactones in Asteraceae Plant Extracts: Evaluation of their Allergenic Potential. Sci Pharm. 2013;81(3):807-818.
  16. Hausen BM. FDA Poisonous Plant Database. 1980. Accessed March 18, 2014.
  17. Miller AD, Ly BT, Clark RF. Neonatal hemolysis associated with nursing mother ingestion of arnica tea. Abstracts of the 2009 North American Congress of Clinical Toxicology Annual Meeting, September 21–26, 2009, San Antonio, Texas, USA [abstr. 120]. Clinical Toxicology. 2009;47:726.
  18. Venkatramani DV, Goel S, Ratra V, et al. Toxic optic neuropathy following ingestion of homeopathic medication Arnica-30. Cutan Ocul Toxicol. Mar 2013;32(1):95-97.
  19. Heck AM, DeWitt BA, Lukes AL. Potential interactions between alternative therapies and warfarin. Am J Health Syst Pharm. Jul 1 2000;57(13):1221-1227; quiz 1228-1230.

Consumer Information

How It Works

Bottom Line: There is some evidence that arnica is effective in healing bruises and osteoarthritis. It has not been studied for any anticancer effects.

Laboratory experiments on arnica have shown that it can kill bacteria and decrease inflammation. However, it is not clear if the herb has similar effects in humans. A few studies have shown that topical arnica applied to affected areas may reduce symptoms of osteoarthritis and heal bruising. Arnica is often used in homeopathic formulas, in which extremely dilute solutions of botanicals and substances are taken by mouth. More research is needed to determine whether they are effective.

Purported Uses
  • To reduce swelling
    There is some evidence that arnica reduces swelling. More studies are needed.
  • To treat sprains and muscle pain following exercise
    Clinical trials do not support this use.
  • As a post-operative antibacterial agent
    Arnica has antibacterial effects, but human data are lacking.
  • To reduce symptoms of osteoarthritis
    Arnica was shown in a few studies to be effective against osteoarthritis.
  • To reduce bruising
    A small study found that arnica ointment was more effective for bruise healing than low-concentration Vitamin K formulas.
Research Evidence

Pain
Fifty-three subjects received two tubes of cream: one containing arnica and the other containing placebo. The creams were applied to the right or left calf as directed on tube labels immediately after calf-raise exercises, and again 24 and 48 hours after exercise. Compared with placebo, the sensation of pain increased in the arnica group after 24 hours. Pain scores were not different between the two groups at 48 and 72 hours after exercise.

Bruise healing
In this study, 16 patients had two bruises created on both upper inner arms to test 4 different topical agents: vitamin K, vitamin K+retinol, arnica, or white petrolatum. Patients were randomly assigned on which agent to use with each of their bruises for 2 weeks. Improvement in bruise healing was greater for arnica than for white petrolatum or vitamin K+retinol.

Osteoarthritis
This study included 204 outpatients with osteoarthritis at various medical centers. Patients were randomized to receive topical ibuprofen or arnica gel 3 times daily for 3 weeks. They could also use acetaminophen tablets as a “rescue treatment” if pain was unbearable. Arnica had similar effectiveness to topical ibuprofen with respect to relieving pain and stiffness, and intake of additional rescue treatment.

Patient Warnings

Accidental overdose with homeopathic arnica has caused severe side effects.
Oral intake of pure arnica can also result in serious to severe side effects.

Do Not Take If
  • You are taking warfarin or other blood thinners: Arnica may increase their effects.
  • You are having surgery: In the lab, arnica has been shown to prevent the formation of clots.
  • You have open cuts, wounds, broken skin: Arnica creams or ointments should not be applied to these areas. It should also be avoided on mucous membranes as it may irritate these areas.
  • You are pregnant or nursing: Arnica tea ingested by one mother caused serious side effects in her breast-fed newborn.
  • You are allergic to sunflowers, marigolds, ragweed or other members of Asteracea family.
Side Effects

Pure arnica herb is considered unsafe and can cause serious side effects.

Topical and homeopathic arnica are generally considered safe, but there has been a reported overdose with homeopathic arnica (see below).

Case reports
Oral, raw herb: Gastrointestinal distress, internal bleeding, rapid heartbeat, shortness of breath, and coma.
Oral, homeopathic overdose: Severe vomiting followed by acute vision loss in both eyes after accidental overdose.
Oral, infant exposure through breast-milk: Breakdown of red blood cells in a 9-day-old breastfed infant 48 hours after his mother began drinking arnica flower tea.
Topical: Rash, skin inflammation at area of contact.

Special Point
  • Topical arnica generally should not be used on broken skin, open wounds, or mucous membranes.
  • Raw or pure arnica herb is considered unsafe by the FDA and should be avoided.
E-mail your questions and comments to aboutherbs@mskcc.org.