True arnica (Arnica montana) [1], known as arnica or mountain arnica, is a plant of the genus Arnica within the aster family (Asteraceae). It thrives in the mountains of Europe and is a protected species. Arnica montana was named Flower of the Year in 1986 and Medicinal Plant of the Year in 2001. It is considered a poisonous plant [2]. The main active ingredients in arnica flowers are in esterified form, particularly helenalin and dihydrohelenalin esters (https://de.wikipedia.org/wiki/Sesquiterpenlactone). Plants in Central European regions contain more helenalin, while dihydrohelenalin predominates in Spain. In addition, the yellow flower heads of arnica contain flavones, flavonols, and essential oil, including thymol, thymol methyl ether, and azulene. Furthermore, triterpenes, phenolic carboxylic acids, polysaccharides, and the terpenoids 2,5-dimethoxy-p-cymol, arnicolides A, B, C, and D, as well as arnifolin, have been identified in arnica flowers [1].
The anti-inflammatory effect of arnica is mainly attributed to the sesquiterpene lactone helenalin [3]. In vitro, helenalin and its derivatives inhibit NF-kappaB and telomerase activity and impair protein and DNA synthesis. In vitro, helenalin induces apoptosis in activated CD4+ T cells by triggering the mitochondrial apoptotic pathway. Furthermore, helenalin suppresses the nuclear translocation of NFATc2 in activated CD4+ T cells [4].
Data from studies using Arnica mother tincture and 1C, 3C, 5C, and 9C dilutions demonstrated an inhibitory effect on TNF-α, IL-6, COX-2, MCP-1, and ICAM-1, as well as reactive oxygen species, in various human and murine cell culture models [5]. In vitro, Arnica stimulated the expression of three genes encoding regulatory proteins of the extracellular matrix, namely fibronectin 1, low-density lipoprotein receptor-related protein 1, and heparan sulfate proteoglycan 2, and may thus potentially influence in vitro cell adhesion and migration during tissue development and healing [6].
In a rat model of collagen-induced arthritis, oral administration of arnica flower methanol extract reduced clinical symptoms and improved joint function in the hind limbs. Treated rats exhibited lower expression levels of nitric oxide, TNF-α, IL-1β, IL-6, and IL-12, as well as a lower titer of anti-type-II-collagen antibodies, compared to untreated animals [7].
In Germany, approximately 200 preparations containing arnica are listed, including numerous homeopathic preparations [9].
Several arnica preparations are available as over-the-counter herbal medicines [8], such as:
A PubMed search for scientific articles on the keyword “Arnica montana” yielded (as of July 31, 2025) 420 references, and 185 for the keyword “Helenalin.” Of these, 62 are clinical studies. These primarily concern non-inflammatory rheumatological indications such as postoperative pain, edema, wound healing following orthopedic, dental, and plastic surgery procedures (e.g., facelifts), as well as degenerative joint changes.
A meta-analysis of 28 studies examined the effect of arnica before or after surgery to improve wound healing, stop bleeding and swelling, and relieve pain. All comparisons with placebo (18 placebo-controlled studies) yielded an insignificant (<0.2) and non-significant effect size (p = 0.059). Studies with active comparators (NSAIDs, acetaminophen) showed a highly heterogeneous, statistically significant, but small effect size of g = 0.26 [10].
In a randomized, double-blind, placebo-controlled study involving 53 participants, the effect of Arnica cream on subjective leg pain was investigated following a standardized calf-raising protocol as part of a training regimen. Each participant received two tubes of cream, one containing active Arnica (right leg) and one containing a placebo (left leg). No significant differences were observed in pain scores prior to training (Arnica: 0.07 vs. placebo: 0.09, p = 0.32). Instead of alleviating leg pain, Arnica increased leg pain 24 hours after eccentric calf exercises. This effect persisted when measured after 48 hours [11].
An open-label, multicenter, uncontrolled clinical trial investigated the use of an arnica gel in patients with mild to moderate knee osteoarthritis. After six weeks, a significant improvement was observed in WOMAC scores regarding pain, stiffness, and function. The treatment was well tolerated, with a low rate of local side effects [12].
A randomized double-blind study in patients with polyarthritis of the fingers showed no difference in the effect on pain and functional limitation between ibuprofen (5% gel) and arnica (50 g tincture/100 g gel, drug-to-extract ratio 1:20) after 21 days in 174 patients [13].
Arnica montana is primarily used to treat postoperative pain and degenerative joint diseases such as osteoarthritis [10, 14]. Clinical data on the treatment with Arnica in patients with inflammatory rheumatic diseases are currently unavailable. The effects of components from Arnica montana on inflammatory mediators in vitro and in vivo do not out rule therapeutic potential. However, there is currently insufficient scientific evidence for the use of Arnica montana in the treatment of inflammatory rheumatic diseases. There are no systematic controlled clinical trials of Arnica montana as monotherapy in patient cohorts with clearly defined inflammatory rheumatic conditions. Due to potential toxicity, systemic use is not recommended.
Oral use of herbal arnica products should be avoided due to the presence of toxic compounds [15]. The medicinal formulations used in homeopathic and commercially manufactured products contain sometimes highly diluted herbal extracts. However, dosing is not standardized across all products, leading to varying concentrations of active ingredients among different manufacturers. Furthermore, the active ingredient content of the plants can vary considerably depending on their geographical origin [16]. This illustrates that higher doses may be associated with safety risks [15].
Preclinical studies showed that the oral lethal dose 50 (LD50) in mice was 512.5 mg/kg body weight. Another study showed that the LD50 for arnica in rats was 54.7 mg/kg body weight [17].
In clinical studies, dermatological side effects were frequently reported with topical arnica use. Contact dermatitis may develop, leading to rash, itching, and dry skin [18]. In addition, patients taking oral arnica products reported gastrointestinal side effects, dry mouth, headaches, drowsiness, and lethargy [19]. The use of arnica during treatment with anticoagulants or antiplatelet agents was not recommended due to an increased risk of bleeding [20]. Due to a lack of data and potentially toxic ingredients, the use of arnica during pregnancy is considered unsafe [20]. One study documented hemolytic anemia and elevated bilirubin levels in an infant, which were likely caused by the mother’s intake of arnica [21].
Although some studies show positive effects in the treatment of pain and inflammation following surgical procedures as well as in the treatment of osteoarthritis, there are limitations in the scientific evidence. Many available studies exhibit methodological weaknesses, such as small sample sizes or the absence of placebo controls; there is a lack of comprehensive data on safety with long-term use, particularly at higher dosages, as well as a lack of consistent standardization of the preparations. The concentration of the active ingredient varies between products, which complicates comparability and dosing.
The scientific evidence is insufficient to recommend the prescription and use of Arnica montana for patients with symptoms resulting from a defined inflammatory rheumatic condition. Topical application of Arnica montana in patients with osteoarthritis should not be discouraged if the patient wishes to pursue this therapy.
Last updated: September 28, 2024