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.
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 Studies on whether arnica can speed healing of bruises are mixed.
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.
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.
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.
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). Arnica may reduce bruising from rhinoplasty (20)(21), but was not helpful after blepharoplasty (22). Rigorous research is needed to determine the clinical benefits of homeopathic arnica.
Mechanism of Action
Sesquiterpene lactones, the active constituents in arnica, have anti-inflammatory properties and inhibit binding of transcription factors AP-1 and NF-κB to DNA (14). A tincture prepared from arnica flowers 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).
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).
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.
The FDA has classified pure arnica as an unsafe herb (16), and oral intake of arnica 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).
Antiplatelet agents: Arnica inhibits platelet aggregation in vitro (12). Warfarin or other anticoagulants: Arnica may potentiate their effects (19).