Arnica

• Arnica is for unbroken skin only. Do not swallow arnica plant products.. The EU herbal committee only covers arnica flower products for the skin. It says arnica preparations can be toxic when taken by mouth and should not be used internally, including as tea, and calls internal use obsolete. Swallowing arnica products has caused severe gastroenteritis, nervousness, fast or slow heart rate, muscle weakness, collapse and death in older reports. The main toxic compound named is helenalin. Authoritative guidance ^{14 34}
• Arnica on the skin can cause an allergic rash, especially in people allergic to daisy-family plants.. Arnica belongs to the daisy family (Asteraceae, also called Compositae). The EU monograph lists allergy to arnica or to other plants of this family as a reason not to use it. Itching, redness and eczema can happen; the frequency is not known. In one skin-clinic patch-test series 5 of 443 people (about 1.13%) reacted to arnica. Authoritative guidance ^{15 12 38 36}
• Do not put arnica on broken skin, near the eyes or on mucous membranes.. The monograph says the preparation should not be used on broken skin or near the eyes or mucous membranes, and that tinctures must be diluted. Undiluted tincture or strong preparations can cause blistering or even tissue death in the skin according to the EU assessment report, which quotes older sources. Authoritative guidance ^{15 14}
• Homeopathic arnica pills are a different product from herbal arnica, but a large swallowed amount caused serious harm in one case.. Homeopathic arnica is a very diluted product swallowed as pills or drops. The EU assessment report says it is completely different from the herbal preparations of the monograph. Pills at normal dilutions are generally mild in trials, but one person who mistakenly swallowed a large amount of Arnica-30 had severe vomiting and then lasting damage to the optic nerves in both eyes. Do not swallow large amounts of any arnica product. Case report ^{14 52}
• Pregnancy and breastfeeding: use is not recommended because safety is not established.. The EU monograph says safety in pregnancy and breastfeeding has not been established and use is not recommended. No fertility, reproductive-toxicity, genotoxicity or carcinogenicity tests have been done on the monograph preparations. The assessment report also quotes an infant with haemolytic anaemia after the mother drank arnica flower tea. Authoritative guidance ^{15 14}
• Blood thinners: a theory and one case report, not an established interaction.. A test-tube study found an arnica flower extract reduced platelet clumping, and the EU assessment report quotes one case of a raised INR in an 81-year-old woman on warfarin who used a large amount of topical arnica. The EU monograph says no interactions are reported. A trial of homeopathic arnica in healthy volunteers found no effect on clotting tests. If you take warfarin or other blood thinners, ask your doctor or pharmacist before using arnica. Pharmacological theory ^{15 14 41 4}
• Skin use is meant to be short. See a doctor if symptoms last 3 to 4 days.. The EU monograph advises seeing a doctor if symptoms last more than 3 to 4 days or get worse. The assessment report says prolonged treatment can cause swollen, blistering dermatitis or eczema. Authoritative guidance ^{15 14}
• A trial found more pain, not less, after arnica cream on exercised legs.. In one trial of 53 volunteers, leg pain 24 hours after calf exercises was higher on the arnica-treated leg than on the placebo leg (3.04 vs 2.36). This did not last to 48 hours. It shows results can go either way and that reactions to the cream are possible. Controlled trial ¹

We found no published human case of liver injury caused by arnica used on the skin. In mice, a single injected dose of helenalin (25 mg/kg) raised the liver marker ALT, though liver tissue itself showed no change on examination (quoted in the EU report). LiverTox was not read. ^{14 15}

How often. No frequency of human liver injury was found. Absence of reports is not proof of safety, and no human liver test data from the trials are given in the abstracts read. The EU report says no data exist for people with impaired liver or kidney function.

Monitoring. No agency monitoring advice was found. People with liver disease should ask a doctor before using arnica, and should not swallow it.

This is a safety connection. It is not evidence that Arnica supports liver health.

Summary. Arnica flower heads contain helenalin-type sesquiterpene lactones. These give the plant its anti-inflammatory activity and also its allergic and toxic effects. On the skin the main problems are allergy and irritation. Swallowed as plant material, arnica is poisonous.

Animal. Single-dose studies quoted in the EU report: the oral LD50 of an unspecified extract was more than 5 g/kg in rats and 123 mg/kg in mice. For helenalin injected into the abdomen the LD50 was 43 mg/kg in one mouse study, and 85 to 150 mg/kg (route not stated) across mice, rats, rabbits and hamsters. In mice a single injection of 25 mg/kg raised liver and kidney blood markers (ALT, LDH, BUN), repeated doses affected the thymus, spleen and lymph-node lymphocytes and lowered liver P450 enzymes. Rat tests of arnica tincture on the skin found most sesquiterpene lactones absorbed into the skin, blood levels below the detection limit and no irritation or dermal toxicity at the amounts tested.

Human doses studied. Skin gels, creams and ointments were studied for 2 to 6 weeks in trials. A tincture was used on the skin for 30 to 45 days in a small trial. No oral arnica plant-material doses were studied in the trials read; homeopathic dilutions were studied separately.

High dose or long term signals. The EU report says prolonged skin treatment can cause oedematous dermatitis with pustules, and eczema; and that higher concentrations can cause blistering or tissue damage. Serious but non-fatal symptoms followed swallowing 30 mL of a 20% tincture.

Overdose response. The EU report says no case of overdose with the monograph preparations (skin use) has been reported. Swallowed arnica has caused gastroenteritis, heart-rate changes, collapse and paralysis in older sources. For homeopathic Arnica-30, a case report describes vomiting and optic nerve damage after a large mistaken intake.

Genotoxicity. No guideline tests exist for the monograph preparations (EMA). An arnica extract was mutagenic in the Ames test, which the authors linked to flavonols; helenalin itself was not mutagenic in two Ames tests (quoted in the EU report). No carcinogenicity or reproductive toxicity data.

Toxic plant parts. The flower heads are the part used and contain the helenalin-type compounds; the EU report says the flower is irritant to mucous membranes. The cosmetic safety report notes that the name Arnica montana is also used for plant material from the roots or rhizomes. Use of the plant in teas or by mouth is the highest-risk exposure.

Arnica products vary in chemistry and may be adulterated or mislabelled.

Adulteration with other daisy-family flowers. The EU report lists adulteration with Chrysanthemum segetum, Crepis biennis, Hieracium, Hypochoeris, Picris hieracioides, Taraxacum officinalis and Tussilago farfara, and says the most common substitute is Mexican arnica (Heterotheca inuloides). ¹⁴

Chemistry depends on where the flowers grew. Flowers from central and eastern Europe contain mostly helenalin esters; flowers from the Iberian peninsula contain almost only 11 alpha,13-dihydrohelenalin esters, and the two types differ in potency. The European Pharmacopoeia requires at least 0.4% sesquiterpene lactones in the dried flower. ^{43 14}

Homeopathic versus herbal products. Homeopathic arnica is made from different parts of the plant, often the whole plant, and is diluted. It is not the same as the flower-head preparations covered by the EU monograph. ¹⁴

• Swelling of the face, lips or tongue, trouble breathing or a spreading hive-type rash after using arnica: get urgent medical help.
• Blisters, weeping or spreading rash, or skin that turns dark or breaks down where arnica was applied: stop using it and see a doctor.
• Anyone who has swallowed arnica plant products or a large amount of homeopathic arnica: vomiting, abdominal pain, a fast, slow or irregular heartbeat, weakness, confusion or collapse: call emergency services or a poison control centre.
• Sudden loss or dimming of vision, or eye pain, after swallowing arnica or after arnica reached the eye: emergency care.
• A breastfed baby who becomes pale, yellow or very sleepy after the mother used or drank an arnica product: seek medical help.
• Unusual bleeding, nosebleeds or bruising while taking a blood thinner and using arnica: contact your doctor.

Stop the supplement and contact a clinician or emergency service. In the US, Poison Control is 1-800-222-1222.