Medically reviewed by Drugs.com. Last updated on May 6, 2020.
Scientific Name(s): Arnica chamissonis subsp. foliosa (Nutt.) Maguire, Arnica cordifolia Hook., Arnica fulgens Pursh., Arnica montana L., Arnica sororia Greene
Common Name(s): Arnica flos, Leopard's bane, Mountain snuff, Mountain tobacco, Sneezewort
Arnica and its extracts have been widely used in folk and homeopathic medicine as a treatment for acne, boils, bruises, rashes, sprains, pains, and wounds. There does not appear to be sufficient evidence to support the use of arnica as an anti-inflammatory or analgesic agent or in the prevention of bruising. Heterogeneity of doses, delivery forms, and indications in available clinical studies also makes generalization difficult.
Arnica is classified as an unsafe herb by the US Food and Drug Administration (FDA) because of its toxicity and should not be administered orally or applied to broken skin where absorption can occur. No consensus exists on topical dosing, and evidence from clinical trials is lacking to support therapeutic dosing. In homeopathic use, less concentrated strengths, such as 12C, 200C, 1M (1,000C), and 10M (10,000C) (C = centisimal dilution [1 part in 100]; M = millesimal dilution [1 part in 1,000]), are recommended for use before and after surgery.
Contraindications have not been identified.
Avoid use. Uterine stimulation has been documented.
None well documented.
Homeopathic doses of arnica are unlikely to result in any adverse reactions because of the small amount ingested. Arnica irritates mucous membranes and causes stomach pain, diarrhea, and vomiting. Allergy and contact dermatitis have been reported.
The plant is poisonous and ingestion can cause gastroenteritis, dyspnea, cardiac arrest, and death. The flowers and roots of the plant have caused vomiting, drowsiness, and coma when eaten by children.
- Asteraceae (daisy)
Arnica, a perennial native to the mountainous regions of Europe and southern Russia, grows from 0.3 to 0.6 m tall. Oval-shaped, opposite leaves form a basal rosette at the soil surface. Arnica has bright yellow, daisy-like flowers that, when dried, are the primary parts used medicinally. Roots and rhizomes may also be utilized. Arnica is sometimes called wolf's bane; however, this name more commonly refers to the unrelated plant monkshood (Aconitum spp.). Lychnophora ericoides is known as false arnica or arnica-da-serra.1, 2, 3
Internal and external preparations made from the flowering heads of arnica have been used medicinally for hundreds of years. Arnica was used extensively in European folk medicine, and alcoholic tinctures were produced by early North American settlers to treat sore throats, as a febrifuge, and to improve circulation. Homeopathic uses include the treatment of surgical or accidental trauma, use as an analgesic, and the treatment of postoperative thrombophlebitis and pulmonary emboli. Arnica has been applied externally to acne, bruises, sprains, and muscle aches. In addition, it has been used as a general topical counterirritant and a CNS stimulant, as well as an antibacterial for abrasions and gunshot wounds. Arnica is also an ingredient in hair tonics, dandruff treatments, perfumes, and cosmetics. A. montana and A. chamissonis subsp. foliosa have been approved for external use in the Complete German Commission E Monographs.2, 4, 5 However, arnica is classified by the FDA as an unsafe herb.
A number of flavonoid glycosides have been identified in arnica. Flavonoids (0.4% to 0.6%) include betuletol, eupafolin, flavonol glucuronides, hispidulin, isorhamnetin, luteolin, patuletin, spinacetin, tricin, 3,5,7,-trihydroxy-6,3′,4′-trimethoxyflavone, kaempferol, quercetin, kaempferol and quercetin derivative, jaceosidin, and pectolin-arigenin. Isomeric alcohols include arnidiol and foradiol. Terpenoids in arnica include arnifolin, arnicolide, and the sesquiterpenes helenalin (and derivatives) and dihydrohelenalin. The pseudoguaianolide ester helenalin methacrylate has been isolated from the flowers. The quantity of sesquiterpene lactones varies widely among species and geographical locations, making standardization of preparations difficult. The European Pharmacopoeia recommends a minimum sesquiterpene lactone content of 0.4% in A. montana preparations used as herbal medicines.6
Amines in the plant are betaine, choline, and trimethylamine. Coumarins include scopoletin and umbelliferone. Carbohydrates, such as mucilage and polysaccharides (eg, inulin), are found in arnica. Two homogeneous polysaccharides, an acidic arabino-3,6-galactan-protein, and a neutral fucogalactoxyloglucan have been isolated. Further polysaccharide isolation has been performed on a group of water-soluble acidic heteroglycans. Volatile oils (0.3% to 1%) may be obtained from rhizomes and roots or from flower parts and are used in perfume. Constituents in the oil include thymol, its derivatives, and fatty acids (eg, palmitic, linoleic, myristic, linolenic). The fatty acid content in arnica leaf essential oil has been evaluated as well. Other components found in arnica include the bitter compound arnicin, caffeic acid, carotenoids (alpha- and beta-carotene, cryptoxanthin, lutein), phytosterols, resin, tannins, lignans, and anthoxanthine.7, 8, 9, 10, 11, 12, 13
Uses and Pharmacology
Controversy exists concerning evaluations of the clinical efficacy of homeopathic arnica. Criticisms of clinical trials include publication bias, sample size, and intention-to-treat analysis. Although topical arnica preparations differ from homeopathic arnica, outcome measures such as pain, inflammation, and coagulation assays have been used as a standard measurement of effect.14, 15, 16 Heterogeneity of doses, delivery forms, and indications in available clinical studies also makes generalization difficult.
A systematic review of trials prior to October 1997 found no evidence for arnica in reducing inflammation.20 Additional trials revealed no difference in swelling or wrist circumference compared with placebo following carpal tunnel surgery,21, 22 equivalence (no difference) to diclofenac 50 mg 3 times daily for swelling after foot surgery,23 and no difference in swelling after knee surgery except for cruciate ligament surgery (pooled data from 3 individual trials).24 In 1 study in postrhinoplasty ecchymosis and edema, patients who received arnica had less edema during the early postoperative period compared with controls, suggesting that arnica has a beneficial effect on postrhinoplasty inflammation.25 Overall, there is insufficient evidence to support the use of arnica as an anti-inflammatory agent.8, 15, 20, 26
The availability of clinical trial data makes findings from animal studies less important.
A systematic review of trials prior to October 1997 found no evidence for arnica as an analgesic.20 Studies evaluating the efficacy of arnica gel compared with ibuprofen gel in osteoarthritis suggest equivalence.27, 28 However, methodological weaknesses exist in the studies.26, 29 No difference in pain following knee or foot surgery, tonsillectomy, or surgery for carpal tunnel syndrome has been found between arnica and placebo.21, 22, 23, 30, 31, 32
The sesquiterpene lactones helenalin and 11-alpha, 13-dihydrohelenalin inhibited platelet aggregation by interacting with platelet sulfhydryl groups in vitro.33, 34 Wound healing following topical application of arnica has been studied with limited success in rats.35
A case report of extensive bleeding during orthognathic surgery attributed to previous consumption of arnica exists.36 However, arnica did not affect blood coagulation parameters in a randomized, controlled trial.15, 37, 38
No difference was found between arnica and placebo for laser-induced or surgical bruising,22, 39, 40, 41 despite arnica being widely recommended for this purpose.42, 43 Following rhytidectomy (face-lift), a decrease in bruising was observed on days 1 and 7, but not days 5 and 10.15 Another study in patients with upper eyelid dermatochalais undergoing blepharoplasty found no benefit in size or severity of ecchymosis or ease of recovery with A. montana compared with placebo; results were confirmed by a double-blind, randomized controlled trial44, 64. An open-label study evaluated the use of arnica powder in umbilical cord care. No infections were noted and stump detachment was unaffected; however, the study had no comparator agent.45
Pooled data from 2 trials evaluating muscle soreness and cell damage in marathon runners reached statistical significance for muscle soreness but showed no difference in relevant cellular enzymes.47 A subsequent trial reported no difference for muscle soreness in marathon runners.25 A small (N = 22) study found reductions in pain 3 days after exercise but no effect on markers of muscle damage or inflammation with topically applied arnica.48 In a study of 53 participants, topical arnica increased calf muscle pain at 24 hours after exercise but not at 48 hours.49
A review of practice patterns of facial plastic surgeons found a commonly cited regimen of A. montana 500 mg capsules taken orally every 8 hours on the day of surgery and continued for 3 days.42
No consensus exists on topical dosing, and evidence from clinical trials is lacking to support therapeutic dosing.8, 15, 20 Experiments show that absorption of active chemical constituents is dependent on the concentration and form of preparation. Microemulsion preparations exhibit greater absorption, as do more concentrated forms of the tincture.6, 58 Creams typically contain arnica oil 15% and salves have arnica oil 20% to 25%.8
Clinical evidence is lacking to support therapeutic dosing. Less concentrated strengths, such as 12C, 200C, 1M, and 10M, have been used in surgery. Because paradoxical effects, such as causing bleeding instead of preventing bruising, can be observed, pre- and postoperative homeopathic use of arnica should be limited.57 (C = centesimal dilution; potency is based on the ratio of 1 part substance to 99 parts dilution.) Designated with a C (or left blank in Europe) after the remedy name, C potencies are considered medium potencies. C potency is often used for seasonal problems and chronic conditions. M = millesimal dilution; potency is based on the ratio of 1 part substance to 1,000 parts dilution. Designated with an M after the remedy name, M potencies are considered high potencies. M potency is used by practitioners for constitutional treatment.16, 44
Pregnancy / Lactation
Avoid use. Uterine stimulation has been documented. Arnica was traditionally used as an abortifacient, possibly due to oxytocic action of constituent sesquiterpene lactones.2, 4 Homeopathic arnica is widely used after childbirth to reduce bruising and postpartum bleeding.59, 60
None well documented. The potential for interactions with anticoagulants has been described; however, no evidence of increased bleeding times or changes in coagulation assay tests were observed in healthy volunteers.15, 34, 38, 61
Homeopathic doses of arnica are unlikely to result in any adverse reactions because of the small amount ingested15; however, a case report exists of toxic optic neuropathy following ingestion of homeopathic arnica.62 Oral ingestion of arnica (eg, tincture, flowers, roots, rhizomes) has caused stomach pain, diarrhea, and vomiting and irritates the mucous membranes, although no adverse events have been reported in clinical trials.2, 15, 38 Numerous cases of allergy and contact dermatitis related to arnica have been described; sesquiterpene lactones helenalin, helenalin acetate, and helenalin methacrylate are the primary sources of contact dermatitis. Chemical and animal experimentation found a topical sensitizing effect.2, 17
Arnica is classified as an unsafe herb by the FDA because of its toxicity. Internal use of arnica and its extracts is not recommended because the plant is considered poisonous.2, 4, 15 The cardiotoxicity of the plant's helenolide constituents has been determined in animal studies.61 Gastroenteritis has occurred with high oral dosages, and dyspnea, cardiac arrest, and death may occur.63 The flowers and roots of the plant have caused vomiting, drowsiness, and coma when eaten.2, 4, 15
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