Arnica montana, an herb that also known as wolf’s bane, leopard’s bane and mountain arnica, is not safe for anyone, including pregnant women, to take by mouth, according to the University of Maryland Medical Center. Arnica is also used as a topical treatment or as part of homeopathic medications, where the concentration of active ingredients becomes miniscule to non-existent after dilution. The United States Food and Drug Administration classifies arnica as a poisonous plant. Ask your physician before using arnica in any form during pregnancy.
Arnica can act as a uterine stimulant, possibly causing contractions that could lead to miscarriage or preterm labor if you take it during pregnancy.
Topical Side Effects
When used topically to treat bruising, sprains, muscle aches, joint pain, inflammation or swelling, this herb can cause skin irritation, including blistering, burning, rashes or other skin irritations. Do not use on broken skin; when the skin barrier is breached, some of the drug could be absorbed systemically, which could cause the same effects as taking the drug orally.
Internal Side Effects
Arnica can have severe, even fatal side effects whether you’re pregnant or not. Taking this herb by mouth in doses other than homeopathic doses can cause low blood pressure, dizziness, tremors, rapid heartbeat, gastrointestinal symptoms, shortness of breath, coma and death.
When you’re pregnant, you’re best off to avoid any potentially harmful substance. Since arnica could have extremely harmful effects to you or your baby if you ingest or absorb enough of it, your safest bet is to avoid it completely. Homeopathic formulations probably do not contain enough of the herb to cause harm, but homeopathic drugs are not regulated and tested in the same way as other drugs and may contain more or less of a substance than they claim.