How It Works
Bottom Line: There is NO proof that arnica works. Homeopathic medicines are so dilute that they probably do not have any effects in the human body. Laboratory experiments on arnica have shown that it can kill bacteria on contact, decrease inflammation, stimulate the respiratory system, and increase the force of heart contractions. However, these effects have only been seen in the laboratory setting, and It is unclear whether they take place in the human body. Arnica is often used in homeopathic medicine, in which extremely dilute solutions of botanicals and substances such as arnica are taken by mouth.
Homeopathic solutions are so dilute that it is doubted whether they have any biological activity at all, and some researchers have proposed that the "placebo effect" (i.e., effect resulting from the expectation that the medicine will work) is responsible for the positive effects of these preparations.
Purported Uses
To reduce swelling
Clinical trials do not support this use.
To treat sprains and muscle pain following exercise
Clinical trials do not support this use.
As a post-operative antibacterial agent
Clinical trials do not support this use.
To reduce symptoms of osteoarthritis
One small clinical trial supports this use, but there is no other scientific evidence to support this use.
Research Evidence
Several clinical trials have tested homeopathic preparations of arnica for uses such as pain and swelling after strenuous exercise, post-surgery infections, and post-surgery hematomas. Almost none found any positive effect of arnica for these conditions.
Warnings
- The F.D.A. considers arnica, when taken orally, an unsafe herb. External use appears to pose no risk.
- Ingestion of arnica is not recommended. The effects of arnica on the lungs, heart, and uterus have not been sufficiently tested to justify the risks that are associated with taking this herb orally.
- A fatal case of poisoning has been reported following ingestion of 70 g of arnica tincture.
- This product is regulated by the F.D.A. as a dietary supplement. Unlike approved drugs, supplements are not required to be manufactured under specific standardized conditions. This product may not contain the labeled amount or may be contaminated. In addition, it may not have been tested for safety or effectiveness.
Do Not Take If
You are taking medication to lower your blood pressure (Arnica may lessen their effects).
You are taking warfarin or other blood thinners (Arnica may increase their effects).
Side Effects
When taken orally: Gastrointestinal distress, tachycardia (abnormally fast heart rate), shortness of breath, coma, and death
When used topically: Contact dermatitis (redness and inflammation of the skin), burning
Scientific Name
Arnica montana
Common Name
Mountain tobacco, leopard's bane, wolf's bane, mountain arnica
Clinical Summary
Derived from the flowers and rhizome. The raw herb and the homeopathic arnica have been used in the treatment of bruises. In vitro studies showed that Arnica montana has antimicrobial activities (9). Conclusions from a systematic review point to insufficient evidence to support use of arnica (8). But clinical trials conducted since then suggest benefits of arnica for osteoarthritis (7) (10) and reduction in postoperative swelling (11) and pain (12).
Side effects following oral administration of the herb (but not the homeopathic preparation) include gastrointestinal distress, hypotension, tachycardia, shortness of breath, coma, and death (3) (4). Topical administration is benign, but can cause contact dermatitis, irritation, and burning (1).
Purported uses
Constituents
Amines: Betaine, choline, trimethylamine
Carbohydrates: Mucilage, polysaccharides including inulin
Coumarins: Scopoletin, umbelliferone
Flavonoids: Betuletol, eupafolin, flavonol, glucuronides, kaempferol, luteolin, quercetin, spinacetin, tricin
Terpenoids: Sesquiterpenes, arnifolin, helenalin
Volatile Oils: Thymol
Other constituents: Arnicin, caffeic acid, carotenoids, phytosterols, resin, tannin
(1)
Mechanism of Action
Experimental studies on the effects of arnica preparations have demonstrated antimicrobial, anti-inflammatory, respiratory-stimulant, positive inotropic, and tonus increasing actions. The anti-inflammatory effects are attributed to helenalin, whose actions include a marked antiedemic effect that has been confirmed in experimental models. The external use of arnica preparations can cause dermatitis in individuals sensitized by sesquiterpenes of the helenalin type.
(3)
Warnings
Internal use of arnica is not advised. The effects of arnica on the lungs, heart, and uterus have not been sufficiently tested to justify the risks associated with oral use. A fatal case of poisoning has been reported following ingestion of 70 g of arnica tincture. The FDA considers oral Arnica an unsafe herb. External use appears to pose no risk.
(2) (4)
Adverse Reactions
Common (oral): GI distress, tachycardia, shortness of breath, coma and death
Infrequent (topical): Contact dermatitis, irritation, burning
(5)
Herb-Drug Interactions
Antihypertensives: Arnica may reduce hypotensive effects.
Anticoagulants / Antiplatelets: Arnica may potentiate the anticoagulant effect due to the coumarin constituents. This effect has not been documented in humans. Use with caution.
References
- Newall CA, et al. Herbal Medicines: A Guide for Health-Care Professionals. London: Pharmaceutical Press; 1996.
- Brinker F. Herb Contraindications and Drug Interactions, 3rd ed. Sandy (OR): Eclectic Medical Publications; 2001.
- Schulz V, et al. Rational Phytotherapy, A Physician's Guide to Herbal Medicine, 3rd ed. New York: Springer; 1996.
- US FDA / CFSAN / Office of plant and dairy foods and beverages. Poisonous Plant Database - Vascular Plant List [online] 1999 May 14 [cited 2001 July 12]. Available from: URL: http://vm.cfsan.fda.gov/~djw/plantnam.html
- Blumenthal, et al. Herbal Medicine, Expanded Commission E Monographs. Austin: American Botanical Council; 2000.
- Wichtl M. Herbal Drugs and Phytopharmaceuticals. Boca Raton: CRC Press; 1994.
- Knuesel O, et al. Arnica montana gel in osteoarthritis of the knee: an open, multicenter clinical trial. Adv Ther. 2002 Sep-Oct;19(5):209-18.
- Ernst E, Pittler MH. Efficacy of homeopathic arnica: a systematic review of placebo-controlled clinical trials. Arch Surg. 1998 Nov;133(11):1187-90.
- Koo H, et al. In vitro antimicrobial activity of propolis and Arnica montana against oral pathogens. Arch Oral Biol. 2000 Feb;45(2):141-8.
- Widrig R, Suter A, Saller R, Melzer J. Choosing between NSAID and arnica for topical treatment of hand osteoarthritis in a randomized, double-blind study. Rheumatol Int 2007;27(6):585-91.
- Brinkhaus B, Wilkens JM, Ludtke R, et al. Homeopathic arnica therapy in patients receiving knee surgery: results of three randomized double-blind trials. Complement Ther Med 2006;14(4):237-46.
- Robertson A, Suryanarayanan R, Banerjee A. Homeopathic Arnica montana for post-tonsillectomy analgesia: a randomized placebo control trial. Homeopathy 2007 96(1):17-21.
