The oral use of arnica is currently limited to homeopathic preparations, due to a certain degree of toxicity being observed in past studies when arnica was taken orally in higher dosages.[1]
Notably, one randomized controlled trial (RCT) reported side effects such as dry mouth, headaches, drowsiness, and lethargy with the use of homeopathic arnica tablets,[2] though causality could not be definitively established.
Although infrequent, topical applications of arnica may lead to skin irritation or contact dermatitis, emphasizing the importance of conducting a patch test before applying it to larger areas.[3][4] Moreover, arnica should not be applied to broken skin.
Finally, due to a lack of data, arnica is not recommended during pregnancy or breastfeeding.[5]