Significance

• Arnica is poisonous if ingested by mouth and is only safe for topical use.
  
  

Risks of Ingestion

• If eaten, Arnica causes many harmful effects, including stomach pain, vomiting, diarrhea, shortness of breath, rapid heartbeat, hypertension, heart damage and coma. In some cases, ingestion of Arnica can be fatal.
  
  

Side Effects of Skin Usage

• When applied topically, Arnica causes minor itching. Some patients have an allergy to Arnica and experience redness, irritation and swelling from the plant. This is most common in people with an allergy to daisies, chamomile, marigolds and yarrow.
  
  

Drug Interactions

• Because Arnica is partially absorbed by the skin, it poses a risk for interacting with the prescription blood thinner Warfarin. When taken with Warfarin, Arnica increases your risk of developing uncontrollable bleeding following an accident, injury or surgery.
  
  

Considerations

• Never use Arnica on broken skin, around your eyes or inside of your nose. If you are pregnant or nursing or if you suffer from Crohn's disease or irritable bowel syndrome, avoid using Arnica.