Arnica, a flower used as an herbal supplement, may be useful in treating pain and swelling caused by osteoarthritis when applied topically, as WebMD states. Arnica can be dangerous or fatal when taken orally and can cause effects that include mouth irritation, vomiting, organ failure, bleeding and skin rashes.Continue Reading
Arnica is also used homeopathically as a treatment for acne, bruises, pain, rashes and boils, according to Drugs.com; however, its efficacy in treatment of these ailments has not been proven, and evidence does not support claims that it functions as an anti-inflammatory or anti-bruising treatment. In addition, arnica has a long history and folklore of being used to treat sore throats, to improve circulation, to treat postoperative thrombophlebitis, to calm muscle pain and to stop dandruff.
When applied topically, the only side effects of arnica reported are contact dermatitis, irritation of mucous membranes and some allergic reactions, reports Drugs.com. When taken internally in the very small amounts used in homeopathic treatments, arnica is not likely to cause negative reactions; however, arnica is toxic in larger amounts and can cause cardiac arrest and death. It is also probably dangerous for pregnant women and may increase heart rate and blood pressure and cause bleeding after surgery, according to WebMD.Learn more about Side Effects