In homeopathic treatment, less concentrated strengths of Arnica montana such as a 200 centesimal dilution should be limited to a few doses, according to Drugs,com. As of 2015, there is insufficient clinical evidence to support therapeutic use of Arnica montana as an anti-inflammatory or analgesic agent.
Arnica should not be taken orally, states Drugs.com. The effects of topical dosing is inconclusive, and the solution should not be applied to any area of broken skin where it could be easily absorbed.
In homeopathic medicine, arnica is used to treat boils, acne, bruises, sprains and wounds, states Drugs.com. There are generally no concerns for side effects if taken in minimal amounts; however, it can cause irritation, stomach pain, vomiting, contact dermatitis and allergic reactions.