Arnica is a genus of perennial, herbaceous plants in the sunflower family (Asteraceae). The genus name Arnica may be derived from the Greek arni, “lamb”, in reference to the plants’ soft, hairy leaves. Arnica is also known by the names Mountain Tobacco and, confusingly, Leopard’s bane and Wolfsbane—two names that it shares with the entirely unrelated genus Aconitum.
Arnica plants have a deep-rooted, erect stem that is usually unbranched. Their downy opposite leaves are borne towards the apex of the stem. The ovoid, leathery basal leaves are arranged in a rosette.
They show large yellow or orange flowers, 6–8 cm wide with 10–15 cm long ray florets and numerous disc florets. The phyllaries (a bract under the flowerhead) has long spreading hairs. Each phyllary is associated with a ray floret. Species of Arnica, with an involucre (a circle of bracts arranged surrounding the flower head) arranged in two rows, have only their outer phyllaries associated with ray florets. The flowers have a slight aromatic smell. If taken in the wrong dose it can be very dangerous.
The seedlike fruit has a pappus of plumose, white or pale tan bristles. The entire plant has a strong and distinct pine-sage odor when the leaves of mature plants are rubbed or bruised.
Commercial Arnica preparations are frequently used by professional athletes. According to The Memorial Sloan-Kettering Cancer Center, “A few clinical trials suggest benefits of topical arnica for osteoarthritis; and for affecting significant reduction of bruising compared to placebo or low concentration vitamin K ointments. However, a small study reported that topical arnica actually increased pain 24 hours after calf exercises.
Early studies of topical arnica gels and ointments for arthritis symptoms of the hand and knee — like pain and swelling — have been positive. So far, research is mixed on whether arnica skin treatments can help ease muscle pain.
If eaten, the actual herb is toxic and can be fatal. However, some oralsupplements contain highly diluted arnica. These are considered homeopathic treatments. These low-dose arnica tablets are safe to use and have been studied for muscle pain, diabetic eye damage, and swelling and pain after surgery. More research needs to be done to establish effectiveness for those problems. A study of children with cancer, however, found that homeopathic low-dose arnica may help reduce mouth ulcers related to chemotherapy.
Because of the risks of pure arnica, the FDA classifies it as an unsafe herb. Doctors who practice complementary medicine generally advise against using arnica in any form other than in a highly diluted homeopathic form.