Like its botanical relative true indigo ( Indigofera tinctoria),
wild indigo has historically been used as a source of a deep
blue dye. It was also used medicinally: the natives of North
America used it as a topical treatment for non-healing wounds
and infections of the mouth and throat. The root is the part
used. Currently, wild indigo is primarily used as part of a
standardized four-herb combination said to improve immune
function. This combination contains, besides wild indigo, root,
and white cedar ( Thuja occididentalis). This combination is
hypothesized to have immune-stimulating properties. In a well-
designed double-blind study of 263 people with recent onset of
the common cold, use of this combination significantly improved
cold symptoms as compared to placebo.1 Recovery occurred
approximately 3 days earlier among people taking the herbal
mixture as compared to those taking the placebo. Benefits for
the common cold were also seen in other double-blind, placebo-
controlled studies involving a total of a