The side effects of arnica include throat and mouth irritation, stomach pain, rashes, diarrhea, vomiting, elevated heartbeat and blood pressure, organ failure, heart damage, coma and death. The Canadian government prohibits the use of arnica as an ingredient in food, according to WebMD.
For people who are allergic to ragweed and similar plants, arnica can lead to an allergic reaction, and related plants include chrysanthemums, daisies and marigolds, among others. People who have elevated heart rate, irritable bowel syndrome, Crohn's disease, ulcers or high blood pressure should avoid arnica, as it can exacerbate all of those conditions, states WebMD.
Arnica grows as a flower and is converted to an oral and topical medicine. On the skin, its uses include soothing aches, sprains and bruises as well as the pain associated with arthritis. Acne, cartilage pain, insect bites and chapped lips are other topical uses. Its oral uses include treatment of sore throat and mouth, superficial phlebitis, and gum soreness after wisdom teeth removal and to initiate abortions, as stated by WebMD.
Within food manufacturing, arnica acts as a flavor ingredient in candy, gelatins, puddings, baked goods, drinks and frozen dairy desserts. When it appears in homeopathic remedies, arnica is used at such a weak concentration that its presence is almost indiscernible, notes WebMD.