Arnica montana Helenalin

ARNICA FLOWERS are the flower heads of Arnica montana L, family Asteraceae. The flowers contain sesquiterpenes such as helenalin and dihydrohelenalin which have antiinflammatory and analgesic effects which explain the popularity of Arnica as a remedy for bruises and aches and sprains. It must be stressed that Arnica should not be used internally because of cardiotoxicity. Equally important is the fact that the sesquiterpenes, like most if not all of those from the Asteraceae (e.g. in Chamomile and Yarrow), are highly allergenic and patients must be advised to discontinue use if a skin reaction develops and to avoid Arnica and Chamomile if they are known to have a sensitivity to other Asteraceae such as Asters, Daisies and Chrysanthemums. 

Arnica montana is not recommended for any internal uses. The plant is an irritant to mucous membranes, and ingestion may cause bumiug pain in the stomach, diarrhea, vomiting, giddiness, intense muscular weakuess, collapse, decrease or increase of the pulse rate, shortness of breath, and death. One ounce (ca. 30 mL) of the tincture (1 0.2 or 20%) has been reported to produce serious but uot fatal symptoms (usd 23rd). Evidence suggests that helenalin is responsible for many, if not all, of these toxic effects. " ... 

Reported cases of contact allergic reactions to A. montana preparations are numerous and date from as early as 1844. Cross-reactivity with other plants is also reported (e.g., sunflower, Tagetes, Chrysanthemum). Sesquiterpene lactones, especially helenalin and its derivatives, are known sensitizers. " Data on the safety of Arnica Montana extract, which is made from the dried flower heads of A. montana, are lacking. Ithas an oral LD50 of >5 g/kg in rats, whereas in mice the LD50 was 123 mg/ kg p.o. An extract made from the dried plant showed mutagenic activity in the Ames test, an effect attributed to the flavonol content. ... 

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