Is Boiron Arnica 30c the right pain relief supplement for you? Arnica Montana has been used for centuries as a natural pain reliever. Today, it has grown to be one of the most popular homeopathic medicines throughout the world. Arnica is trusted by professional athletes to relieve sore muscles, by prominent plastic surgeons to ease the post-procedure pain, and by savvy moms to treat playground bumps and bruises.