FYI

Available scientific evidence does not support most of the claims about arnica's effectiveness. A 1998 review in the Archives of Surgery looked at 8 controlled human trials of arnica, and found that arnica worked no better in treating injuries than the placebo with which it was compared. The authors found that the studies they reviewed had serious flaws in the methods used to evaluate the effectiveness of arnica. They concluded that the human trials did not show that arnica was helpful or beneficial. One randomized clinical trial actually found that arnica appeared to increase pain and cause more swelling than the placebo in patients who had their wisdom teeth removed.

A 2003 study of 62 patients tested homeopathic arnica to find out whether it reduced pain and bruising in patients having surgery for carpal tunnel syndrome. There were no differences in pain or bruising between the arnica and placebo groups.

A double-blind, randomized British study of 37 patients looked at homeopathic arnica in tablet and ointment form to learn whether it helped people having surgery for carpal tunnel syndrome. A week after surgery, there were no differences in grip strength, wrist swelling, or pain between the group that was given arnica and the placebo group. Two weeks after surgery, the group that had arnica reported somewhat less pain than the other group, although there were still no differences in grip strength or swelling. Further studies are needed to find out whether this one difference is due to chance or to the effects of the arnica.

In 2002, a small Miami study looked at arnica gel to see whether it would reduce bruising after laser surgery to the face. No difference in bruising was noted between the patients who used plain gel and those who used the arnica gel.

In 2006, German researchers analyzed 3 studies on the use of arnica after knee surgery. Homeopathic arnica was given before and after surgery in all 3 studies. There were no significant differences in swelling after surgery between the arnica groups and the placebo groups in 2 out of 3 of the studies.

A 2007 controlled study looked at homeopathic arnica in patients who had their tonsils removed. One group received arnica and the other a placebo. Patients were surveyed afterward, with 111 out of 190 patients returning their questionnaires. The arnica group reported slightly lower pain levels than the placebo group, although there was no difference in how much pain medicine they needed, the period of time before they went back to work, and the number of visits they made to the doctor afterward. There was also no difference between the groups in bleeding and infection after surgery. A similar outcome was observed in a study published in 2010, in which patients got a mixture of arnica along with another homeopathic remedy after heart valve surgery. There was no difference between the placebo and homeopathic arnica groups in terms of blood loss, pain, fever, or lab results.

A toxicology assessment completed in 2001 concluded that there was not enough safety information on arnica to support allowing its use in cosmetics.

One 1994 study found that some of the chemicals extracted from arnica can kill colon and lung cancer cells growing in laboratory dishes. No follow-up studies in animals or humans have been published since then, possibly due to the side effects that can happen when arnica is taken internally.

Several laboratory studies suggest that arnica may reduce the activity of certain types of immune system cells. However, much more research in animals and humans would be needed to find out whether this effect is helpful or harmful to people with cancer or other diseases.