Herbal preparations of arnica can be poisonous if taken internally as they are strongly irritating to mucous membranes.
This can lead to severe gastroenteritis and muscle paralysis (including cardiac), symptoms of palpitations and shortness of breath, and even death — largely due to the toxic effects of helenalin.
Arnica is considered much safer when used topically, although there have been a few reports of dermatitis using the creams where it can trigger sensitivity to contact allergens.
Arnica is contraindicated in treating rheumatoid arthritis, as in some cases it can increase macrophage-induced local inflammation.
It’s also contraindicated in pregnant or breastfeeding women and those who are allergic to, or have a known hypersensitivity to, members of the daisy family, including chamomile and marigold.
Topical arnica preparations should not be used on broken skin but are safe and effective for sprains, strains, swellings etc.
Arnica should never be taken internally except in homœopathic preparations.
