Arnica grows 1-3 pairs of oblong, ovate basal leaves. The stem terminates by branching into 1-3 peduncles, each bearing a flower which is present from June to August. In Germany, for example, arnica is one of the most prescribed herbal remedies for stimulating the immune system. It is seldom used in North America, and indeed has acquired a somewhat unfavourable reputation in the United States, perhaps due to lack of knowledge about its use.
Arnica is also a common homeopathic remedy for multiple sclerosis.
Arnica's main alkaloids resemble the active alkaloids of echinacea, both in structure and in activity. Has Cardiovascular Action Arnica has been found to strengthen circulation by stimulating coronary heart vessels and by increasing heart capacity. There is such a thing as too much of a good thing, however, and too much arnica extract could produce hypertension and adverse effects on the heart. In support of the immunostimulant property referred to above, it has been found arnica extract stimulated phagocytosis in laboratory animals. Among the bacteria counteracted were Listeria monocytogenes and Salmonella typhimurium.