Herb library · Herb · Iris versicolor
Blue flag
The wild blue iris of North American marshes, whose root was a strong purge in 19th-century medicine. The fresh root is irritating and was known to cause violent vomiting; it has not been studied in people.
Traditional use
King's American Dispensatory (1905) records that the root was highly esteemed by American Indians, who used it for stomach complaints, and that it was a popular household remedy, sometimes called "vegetable mercury," for bringing on salivation. It became one of the most valued medicines of the Eclectic physicians, who used small doses for the liver and glands.
What studies show
No studies in people of this herb on its own yet. What is known of it comes from the traditions that use it.
- Insufficient
Digestion, liver and skin: no study of blue flag in people was found.
Be careful of
Cautions
- AmountDo not take it by mouth at home. King's American Dispensatory (1905) describes the root acting violently in larger doses, with vomiting, purging, burning in the bowels and severe colic, and animals that died after eating it. The fresh root is the most irritating.
- PregnancyNever use it in pregnancy or while breastfeeding.
- NoteBlue flag is easy to confuse with sweet flag (calamus), which grows in the same wet ground; the two are unrelated. Know which one you have.
- Ask a clinicianIf anyone swallows the root and becomes ill, call Poison Control (1-800-222-1222 in the U.S.) or emergency services. Talk with a clinician before any use.
From the old books
What herbals and dispensaries of the past printed. History, in their words.
“This plant was highly esteemed by our American Indians, who used it in gastric affections, and it was also a popular domestic remedy when it was thought necessary to produce salivation without resorting to mercurials”
Sources
- Phytochemical Composition and In Vitro Biological Activity of Iris spp. (Iridaceae): A New Source of Bioactive Constituents for the Inhibition of Oral Bacterial Biofilms (2020) — PubMed record (opens in a new tab) · NIH · read September 25, 2026
Reviewed September 25, 2026.