e200921c_sity_of_Michigan_Health_System__Why
[Supplement] 1 Star Wild Indigo Refer to label instructions [Why] 
Wild indigo appears to stimulate immune function and is considered a strong antimicrobial agent. In tinctures with echinacea, boneset, white cedar, and homeopathic arnica, it also has prevented and reduced colds. According to test tube experiments,73 wild indigo stimulates immune function, which might account for its role in fighting the common cold and flu. In combination with echinacea, boneset, and homeopathic arnica, wild indigo has prevented and reduced symptoms of the common cold in double-blind research. Wild indigo is traditionally considered a strong antimicrobial agent, though it has not yet been investigated as an agent against cold viruses.
Common Cold/Sore Throat (Holistic) | University of Michigan Health System
Why