Blue flag, a member of the iris family, is found throughout North America. It was widely used by Native Americans for digestive problems. In the nineteenth century, physicians of the Eclectic school of medicine also used blue flag for digestive problems, as well as to treat thyroid enlargement, enhance immunity, stimulate the liver, and “detoxify” the body.
A topical preparation of the herb was used for impetigo (a skin infection caused by
bacteria). The rhizome (underground stem) is the part used medicinally.
Blue flag has undergone no meaningful scientific study. In view of the lack of documented benefits, the absence of toxicity studies, the toxicity of related species, and the known side effects, we recommend against the use of this herb.
What Is Blue Flag Used for Today?
Blue flag is used by some herbalists today to treat liver problems and skin diseases. However, there has been essentially no scientific evaluation of the efficacy of this herb. It is thought to contain isophtalic acid, iridin, and the volatile oil furfural.
Blue flag has not undergone any meaningful scientific study. High doses of blue flag are known to cause severe gastrointestinal upset, including nausea, vomiting, and diarrhea, and related species are known to be toxic.
The fresh herb can irritate the mouth and stomach. Blue flag is considered unsafe for use by pregnant or nursing women and young children.