Medicinal Properties of Arnica
Arnica is a daisy-like plant with yellow flowers. Although high oral doses are toxic, it’s used as a cream or homeopathic pills to reduce pain, bruises, swelling from injuries, and speed recovery after plastic or dental surgery. But what’s the difference between herbal and homeopathic arnica and do both work? Read on to find out, along with an evidence-based review and side effects.
What Is Arnica?
Arnica (Arnica montana L.), also known as mountain daisy, mountain tobacco, and leopard’s bane, is a plant with orange-yellow flowers that belongs to the same family as sunflowers, dandelions, daisies, and marigolds (Asteraceae) [R+, R+].
Arnica grows best at an altitude of 500 – 2,500 meters and is native to the meadows and mountainous regions of Europe, western North America, and northern Asia. Because arnica is endangered in several European countries, its cultivation has increased but the harvesting of wild plants is not allowed [R+, R+].
- Soft tissue injuries (e.g., smashed fingers)
- Sprains, strains, fractures, and contusions
- Muscle soreness
- Post-surgical bruises and swelling
Arnica can also be formulated in oral homeopathic pills that are mainly used for [R+]:
- Mouth, gum, and throat inflammation
- Diabetic eye damage
- Post-surgical bruises and swelling
- Muscle soreness
The German Commission E has only approved the use of topical arnica (creams, gels, ointments) for injuries, consequences of accidents, and inflammation (mouth and throat, insect bites, boils, veins). The FDA considers oral arnica unsafe due to its toxicity and the Canadian Government prohibits its use as a food ingredient [R+, R+].
It’s important not to confound Arnica montana with other plants popularly known as “arnicas”, such as Brazilian (Solidago chilensis and Lychnophora spp.) and Mexican (Heterotheca inuloides) arnicas. They belong to the same family and are also used in traditional medicine, but may have different active compounds and applications [R, R, R].
Snapshot of Arnica
- Improves arthritis
- Easy to apply
- Few side effects when applied to the skin or used as homeopathic pills
- Insufficient evidence for most benefits
- Toxic at high oral doses
- Long-term use can irritate the skin
- Endangered species
Active Components of Arnica
The main active compounds of arnica are sesquiterpene lactones such as helenalin, dihydrohelenalin, and their derivatives [R].
Other components of the plant include [R+]:
- Antioxidant compounds (flavonoids, polyphenols, lignans, carotenoids, and chlorogenic acid derivatives) [R, R, R+, R]
- Toxic compounds (alkaloids, polyacetylenes, and coumarins) [R, R+]
- Essential oils [R]
- Sugars [R]
Most active compounds are found in the flowers, which are particularly rich in sesquiterpene lactones (0.5 – 0.9%), flavonoids (0.4 – 0.6%), and essential oils (0.2 – 0.5%). The amount of sesquiterpene lactones increases with flower maturity [R+, R+].
Seeds are the richest in polyphenols and flavonoids [R].
The sesquiterpene lactone composition in flowers strongly depends on geography. Flowers from high altitudes mainly contain helenalin, while those from lower meadows are richer in dihydrohelenalin [R+, R+].
How Does Herbal Arnica Work?
When arnica’s sesquiterpene lactones penetrate the skin, they block the master inflammation pathway, NF-kb, and proteins that trigger an inflammatory immune response (RelA and NF-AT). This prevents the activation, division, and development of Th immune cells and stops them from releasing inflammatory substances (cytokines) [R, R, R, R].
Arthritis and Bruises
Arnica’s sesquiterpene lactones also block the production of two enzymes (MMP1 and MMP13) that degrade collagen in joint cartilages and blood vessels. By preventing collagen breakdown, arnica protects joints from arthritis and strengthens blood vessels [R].
Benefits and Uses of Herbal Arnica
Herbal arnica is formulated into creams, gels, and ointments. These products contain arnica tinctures or dried flowers (1 – 25%) and their effects rely on arnica’s bioactive components (unlike homeopathic pills). Arnica tea can also be used on the skin, but should not be consumed orally.
Creams or ointments should contain a maximum of 15% arnica oil or 20 – 25% tincture [R].
1) Herbal Arnica Is a Natural Pain Reliever
In a clinical trial of 79 people with knee arthritis, arnica gel (2.5% arnica extract) applied 2x/day for up to 6 weeks reduced pain, stiffness, and disability. The same gel 3x/day for 3 weeks reduced hand arthritis symptoms as effectively as a 5% ibuprofen gel in a clinical trial on almost 200 people [R, R].
In rats with arthritis, a high-dose arnica extract (up to 500 mg/kg body weight) reduced joint damage, inflammation, and increased antioxidants [R].
Pain from Traumatic Injuries
A spray for sports injuries with 10% arnica tincture and an anti-inflammatory painkiller (hydroxyethyl salicylate) reduced the pain from ankle distortion and sports injuries in two clinical trials of over 600 people. The combination worked better than either substance alone [R, R].
In a clinical trial on 20 people, 2.5 g of a 1% arnica flower gel applied every 4 hours after a downhill run reduced muscle soreness better than placebo, but only after 3 days [R].
2) Herbal Arnica May Improve Bruises
In a clinical trial on 16 people, a 20% arnica extract ointment applied 2x/day for 2 weeks reduced bruising from a laser procedure. It was as effective as a low-dose vitamin K cream and better than placebo [R].
Steroids are most commonly used to reduce bruises and swelling after plastic surgery. But herbal remedies are also gaining popularity [R].
In a clinical trial on over 100 people undergoing nose plastic surgery, a cream with arnica applied 4x/day for 10 days reduced bruises and swelling. However, a 10% arnica ointment failed to improve bruises and swelling after eyelid surgery in a trial on 136 people [R, R].
3) Herbal Arnica Speeds Up Wound Healing
In newborn babies, the umbilical cord stump takes up to 2 weeks to dry up and fall off. During this period, special care must be taken due to the risk of infections. In an observational study on over 6,000 babies, a powder containing arnica and echinacea 2x/day prevented infections and helped umbilical cord stumps fall off within only 4 days on average [R].
In an observational study on 50 people with chronic wounds, a powder blend with 0.01% arnica and other herbs was rated effective by 85 – 89% of caregivers. The effects could have been due to other, more abundant components of this blend (mint, sandalwood, and calendula) [R].
4) Herbal Arnica May Prevent Infections
In hamsters, an arnica tincture healed skin injuries caused by a parasitic infection (leishmaniasis) better than the more conventional medicine meglumine antimoniate [R].
Arnica extract prevented the growth of several microbes that cause gum disease (Porphyromonas gingivalis, Prevotella spp., Eikenella corrodens, Peptostreptococcus spp., and Actinomyces spp.) in one cellular study [R+].
5) Herbal Arnica May Improve Breathing
In Guinea pigs, an arnica complex safely reduced coughing and widened the airways. Its effects were similar to an anti-asthma drug (salbutamol) [R].
6) Herbal Arnica May Reduce Skin and Gum Inflammation
Arnica creams are sometimes used to reduce skin inflammation and acne, while dental washes can be used to soothe gum inflammation [R].
Based on cellular studies, arnica blocks the master inflammation pathway NF-kB, reducing the production of many inflammatory substances (IL-1, IL-2, IL-6, IL-8, and TNF-alpha). It also blocks the inflammation-triggering enzyme COX-2 (like NSAIDs such as Advil and Motrin – ibuprofen) and reduces the expression of genes that worsen immune over-activation [R].
However, products with high arnica concentrations used over longer periods of time are more likely to cause skin irritation too, especially in people sensitive to similar plants [R].
7) Other Herbal Arnica Uses (Food Industry)
The food industry uses arnica as a flavoring in [R+]:
- Alcoholic and soft drinks
- Frozen dairy desserts
- Baked goods
Benefits and Uses of Homeopathic Arnica
Arnica is often used as a homeopathic remedy. Homeopathic remedies are prepared by diluting the active compound with alcohol or water several times.
What’s the Difference Between Herbal and Homeopathic Arnica?
It’s very important to discriminate between herbal preparations, such as arnica creams and gels, and homeopathic ones. Homeopathic remedies are not the same as herbal tinctures, extracts, and other products used in herbal medicine in an evidence-based way.
Sometimes herbal products are combined with homeopathic remedies. But homeopathy relies on completely different principles, such as the “vital force” and “like cures like” to explain how the remedies supposedly act.
Homeopathy also uses a lot of substances that are toxic in normal, oral doses, including arnica. Substances are greatly diluted in a process called “dynamisation” or “potentisation” and thought to exert an energetic effect on the body.
Homeopathic preparations are commonly critiqued for using such high dilutions that they contain only a few or no molecules of the active compound. Homeopathy does not consider that the effects of the remedies come from the active components of the substance used.
Scientific evidence does not back up the claims made by homeopathy. Indeed, a meta-analysis concluded that homeopathic remedies had no effect beyond placebo [R].
Understanding Homeopathic Dilutions and Doses
Homeopathic dilutions are written as a number followed by a letter (e.g., 30C). The number is the number of times the diluting process was performed. The letter represents the dilution factor, or how much the substance was diluted [R+]:
- X or D: 1/10 means it was diluted 10 times and contains 10% of the active compound; 1 part of extract per 10 of alcohol or water
- C: 1/100
- M: 1/1,000,000
So, a homeopathic arnica remedy labeled as 10X would contain only about 0.000000001% of arnica. One labeled as 30C would contain much less, as it would mean that the substance was 30 times diluted by 100.
Because homeopathic arnica preparations are not standardized, it’s almost impossible to compare the doses of different products. But it’s worthy to note that most of them probably do not contain any arnica at all. The upside of this is that, unless adulterated, they act similar to placebo and won’t cause serious side effects or drug interactions [R+].
1) Homeopathic Arnica May Provide Pain Relief
The evidence isn’t convincing, as homeopathic arnica remedies had either no effect or very slightly improved pain in most of the mentioned studies. Its effects were mostly comparable to the placebo, with some exceptions.
However, pain is especially susceptible to the placebo effect, which shouldn’t be overlooked. The placebo effect can be looked at as therapeutic. It may reduce the use of dangerous painkillers and train people to become active agents of their therapy [R].
The placebo effect, and most probably the pain-relieving effects of arnica, also depend on the healing environment and the practitioner you may come into contact with [R].
A homeopathic ointment with arnica and other components applied 3x/day reduced pain and increased shoulder mobility in a clinical trial on 41 people with shoulder arthritis. However, there was no placebo group in the study [R].
In a clinical trial on 30 people with low-back pain caused by arthritis, 2 homeopathic tablets of arnica (6C) and other plants 2x/day combined with physiotherapy outperformed placebo. They improved pain and disability after 4 weeks but didn’t reduce the use of other painkillers [R].
Pain from Traumatic Injuries
Traumeel, a homeopathic preparation with arnica (3D) and other plants, reduced pain as effectively as conventional medicines in an observational study on over 100 people with ankle, hand, or knee injuries [R].
A 5% arnica ointment combined with homeopathic arnica tablets (6D) 1x/day for two weeks reduced pain but not swelling in a clinical trial on 37 people undergoing carpal tunnel syndrome surgery. But homeopathic arnica tablets alone (6C or 30C) were not better than placebo at reducing pain, bruising, or swelling after this procedure in another trial on 64 people [R, R].
A homeopathic complex with arnica taken before surgery and for 3 days after wasn’t more effective than placebo at reducing pain in a clinical trial of 158 people undergoing knee ligament reconstruction. Similarly, homeopathic arnica (30X) before and after knee surgery only slightly reduced pain and swelling in 21% of the cases in trials on over 300 people [R, R].
In one clinical trial, over 100 people undergoing tonsil removal claimed that homeopathic arnica (30C tablets 6x/day) reduced their pain when taken for a week after surgery. But when the data were analyzed, there was no difference to placebo [R, R+].
In a clinical trial on over 100 people who had their wisdom teeth removed, homeopathic arnica (200C 2x/day) was worse than an antibiotic (metronidazole) and placebo at reducing pain and swelling. In another trial on 24 people, a homeopathic complex with arnica (30D) didn’t improve pain nor inflammation after wisdom teeth removal [R, R].
In a clinical trial on 88 people undergoing bunion removal, homeopathic arnica (10 D4 pills 3x/day) reduced pain less than an anti-inflammatory drug (diclofenac 50 mg). However, it did reduce wound irritation and improved mobility similar to the drug with fewer side effects [R].
In a clinical trial on 73 women, arnica (30C) taken before and for 5 days after uterus removal surgery (hysterectomy) didn’t reduce pain nor infections better than placebo [R].
In 2 trials of 82 runners, homeopathic arnica (5 30C pills 2x/day for 4 days) lowered muscle soreness immediately after a marathon. However, homeopathic arnica (30X and 200C) before and after long-distance runs was not better than placebo in 2 clinical trials on over 500 people. [R, R, R].
In a clinical trial on 53 people, a homeopathic arnica cream (1X) wasn’t better than placebo at improving muscle soreness after doing calf raises. On the contrary, it worsened muscle soreness slightly one day after the exercise [R].
2) Homeopathic Arnica May Improve Bruises
In a clinical trial on 11 people, homeopathic arnica (30C) before and after being bruised didn’t have any effect. In another trial, homeopathic arnica (10M) taken after bruising reduced bruise size more than placebo in 6 out of 13 cases [R].
Homeopathic arnica (1M) 3x/day for 3 – 4 days slightly accelerated the healing of bruises caused by plastic surgery in a clinical trial on 22 people. But it only improved swelling on day 2 in another trial of 48 people [R, R, R].
Homeopathic arnica (1M) taken before eyelid surgery and for 3 days after (12C 3x/day) didn’t reduce bruises in a trial of 30 people [R].
In a clinical trial on 29 people with bruises from face-lift surgery, homeopathic arnica tablets (3x/day) didn’t improve pain nor bruise color after 4 days. They only caused a slight bruised surface reduction that couldn’t be detected without a computer [R].
Other Medical Procedures
In a clinical trial on over 100 people undergoing vein stripping surgery, homeopathic arnica (5C) before and after surgery didn’t prevent nor reduce bruises [R].
Homeopathic arnica pills (6C or 30C 1x/day) for one week before and two weeks after carpal tunnel syndrome surgery didn’t prevent bruising or reduce swelling in a clinical trial on 64 people [R].
A pulsed dye laser is routinely used to remove skin birthmarks and help heal bruised skin. A homeopathic ointment with arnica (1X) wasn’t better than placebo at preventing nor improving bruises in a clinical trial on 19 people [R].
A laryngeal mask keeps airways open during surgery but can cause vocal cord bruising and sore throat. In 2 case studies, homeopathic arnica (200C) reduced sore throat symptoms in 2 days [R].
3) Homeopathic Arnica May Improve Wound Healing
In a clinical trial on 88 people undergoing bunion removal, homeopathic arnica (10 D4 pills 3x/day) was as effective as an anti-inflammatory drug (diclofenac 50 mg) at reducing the redness, swelling, and heat of inflamed wounds [R].
Homeopathic arnica dilutions enhanced wound healing and the production of wound-healing proteins by white blood cells (macrophages) in two cell studies. However, the alcohol used in the dilutions could have contributed to these effects [R, R, R].
4) Homeopathic Arnica May Reduce Bleeding
In a clinical trial on 40 women who recently gave birth, 3 homeopathic pills of arnica (6C or 30C) combined with 3 homeopathic pills of the common daisy (Bellis perennis) every 5 hours for 1 day and 3x/day for 2 additional days reduced blood loss [R].
A combination of homeopathic arnica and bryonia (5C 2x/day) for 5 days after heart surgery didn’t reduce bleeding, inflammation, pain, nor poor blood flow in a clinical trial on 92 people [R].
5) Homeopathic Arnica May Reduce Menopause Symptoms
In a clinical trial on over 100 menopausal women, a homeopathic mixture containing arnica (4C) and 4 other remedies reduced hot flashes better than placebo over 12 weeks [R].
Side Effects and Safety of Arnica
- Digestive problems (gastroenteritis, stomachache, vomiting, diarrhea)
- Mood disturbances (drowsiness, nervousness)
- Muscle weakness
- Increased heart rate
- Shortness of breath
- Coma, and even
- Death from heart failure (very high doses)
In an observational study on 86 women who took in different plants to induce abortion, 2 out of 3 women using arnica suffered multiple organ failure [R].
Because the dose of the active compounds in homeopathic preparations is exceptionally low, homeopathic arnica is generally considered to have no risk of toxicity. However, a person who took in a very high amount (100-200 mL) of arnica 30C suffered from blood-stained vomiting and loss of vision. This could have been caused by the alcohol used in the dilutions [R].
Although topical arnica is generally well tolerated, gels and ointments can cause mild to moderate allergic reactions on the skin in people sensitive to its compounds, such as [R+]:
- Local rash
- Colored spots
The long-term use of arnica can sensitize the skin and increases the risk of allergic skin reactions.
In an observational study on over 400 people with chronic dermatitis, 5 were allergic to arnica. They all reported applying it on the skin or coming into contact with the plant as hobby-gardeners. A person who repeatedly used arnica tincture for a skin condition (rosacea) developed a contact allergy with blistering [R, R].
A person who used an undiluted arnica mouthwash (meant to be diluted 1:5 with water) experienced a burning sensation with each rinse and mouth lining injuries [R].
Importantly, arnica shouldn’t be applied on open wounds or broken, damaged skin to prevent the absorption of too much arnica and its toxicity [R+].
People with an allergy to plants of the same family (Asteraceae) such as marigolds and coneflowers should avoid both oral and topical arnica [R].
- Digestive problems
- High heart rate or blood pressure
- Scheduled surgery (due to reduced blood clotting)
Oral arnica (excluding highly diluted homeopathic remedies) is generally considered unsafe, and especially so for pregnant and breastfeeding women. Indeed, a breastfed baby whose mother was drinking tea made from arnica flowers developed anemia due to red blood cell damage [R].
Drug Interactions of Arnica
- Painkillers/anti-inflammatories (aspirin, diclofenac, ibuprofen, naproxen)
- Blood thinners (clopidogrel, dalteparin, enoxaparin, heparin, warfarin)
Because homeopathic arnica contains few or no molecules of its active compounds, this interaction may only occur in people taking high-concentration (‘low-potency’) pills, such as 3 – 5 D/X. The interaction is more likely with oral herbal arnica use, which is very rare.
High-dose oral arnica is also not recommended in people using drugs for high blood pressure, since it may reduce their effect [R+].
Forms and Dosage of Arnica
Arnica is available as various formulations that can be applied on the skin, such as:
- Tincture: a 1:10 alcoholic extract of arnica flowers
- Oil: essential oil obtained from the distillation of arnica flowers
- Tea (2g herb/100 mL water) only for external use. Only people under strict medical supervision may drink the tea, which is considered dangerous.
- Mouth rinse: a 1:10 dilution of arnica extract
- Homeopathic creams, such as Traumeel
Creams, gels, ointments, and salves typically contain 20 – 25% arnica tincture or 15% arnica oil [R+].
It is important to buy arnica from a reliable source since it is a protected species in some countries. Unreliable manufacturers may include other plants in their products and fraudulently market them as arnica [R].
- Hair tonics
- Preparations for dandruff and acne
- Shampoos and bath gels
- Homeopathic pills or tablets: typically 5C or 30C
- Less diluted, lower ‘potency’, such as 5D, 6D, 10D or 10X
- More diluted, higher ‘potency’, such as 1M or even 50M
- Tinctures: Dilute 3 – 10x with water and apply to the affected area of the skin or dilute 10x to use as a mouthwash [R+].
- Arthritis: Apply a 2.5% arnica extract gel 2-3x/day for up to 6 weeks [R, R].
- Sports injuries: Apply a 10% arnica tincture spray 5x/day for 10 days [R].
- Muscle soreness: Apply 2.5 g of a 1% arnica flower gel every 4 hours for 4 days or take 5 arnica 30C pills 2x/day for 4 days [R, R].
- Bruises due to injuries: Apply 0.25 g of 20% arnica tincture ointment 2x/day for 2 days [R].
- Post-surgical bruises: Apply a cream 4x/day for 10 days or take arnica 1M 3x/day for 3-4 days [R, R, R].
Genetics Related to Arnica
Arnica’s helenalin blocks the activation of the pro-inflammatory protein RelA, which is part of the key inflammation pathway NF-kB. It does so by binding to a specific amino acid (Cys38). Variants of the protein with a different amino acid may increase or reduce the effects of arnica by enhancing or preventing the action of helenalin [R, R].
Limitations and Caveats
For most health benefits, studies reported a mix of positive and negative results. Those using homeopathic remedies most frequently showed no differences between the application of arnica and the placebo.
A lot of the studies were done on a few people (30 or less), which can produce unreliable results.
Study Funding and Conflict of Interest
Several of the studies were funded by companies selling arnica preparations (Bioforce, Boiron, Alpine Pharmaceuticals, Similasan, Cearna) or done by employees of these companies [R, R, R, R, R, R, R, R].
Most people used arnica for bruises, pain, and swelling caused by injuries. Almost all of them reported a fast and strong improvement of the symptoms. People using topical formulations were more satisfied than those taking pills. Only one reviewer who used arnica for sports injuries complained that it didn’t work for him.
Only two users reported adverse effects. One had to wash a cream off immediately due to a burning sensation on the skin and the other one experienced digestive problems after taking the pills.
Similarly, most people using arnica on the skin or as homeopathic pills after plastic surgery reported a fast improvement of bruises and swelling. Only one complained that the pills didn’t work.
Users taking arnica for inflammatory conditions generally reported satisfactory results but were concerned about its possible interaction with blood thinners.