Text Size

Site Search powered by Ajax

Blue Flag

Blue Flag

Botanical Description & Habitat

Iris versicolor


Common Names

Flag lilyFleur-de-lis
Flower-de-luceLiver lily
Poison flagSnake lily
Water flagWild iris

A wetlands perennial, native to eastern North America, exported to Europe.

Medicinal Parts
Dried rootstock, gathered in the fall.

Historical Properties & Uses

Blue flag is defined as a cathartic, diuretic, sialagogue, for use in the treatment of gastrointestinal disorders, including gastritis, heartburn, chronic vomiting, and enteritis. Some sufferers of migraine claim they obtain relief from Blue flag.

In India blue flag has been used for centuries much as curry, i.e., to prevent the absorption of cholesterol. This may have been the basis for the use of this plant in weight control programs in that country.

Blue flag finds its most common modern usage in homeopathic preparations for the treatment of diabetes, gastrointestinal problems, skin problems, liver disorders, headaches of all kinds, nausea, and inflammatory disorders.

Method of Action

Not much is known about the mechanisms of action of blue flag. It does contain essential oil of complicated composition, gums, resins, starch, and some fatty acids.

The British Herbal Pharmacopoeia recognizes blue flag as a cholagogue, laxative, diuretic, dermatological agent, anti-inflammatory, and antiemetic in small doses, for use in the treatment of skin diseases and biliousness with constipation and liver dysfunction, with specific application for cutaneous eruptions.

Combined with yellow dock, red clover, pokeroot and stillingia in skin disease.

Drug Interactions & Precautions

Known Interactions
Blue flag, insofar as its diuretic action increases the renal excretion of sodium and chloride, may potentiate the hyperglycemic and hyperuremic effects of glucose elevating agents.

Diuretics may potentiate the action of antihypertensive, ganglionic or peripheral adrenergic blocking drugs, tubocurarine and norepinephrine. The effects of dopamine and diuretic agents are additive.

Blue flag, due to its cathartic activity, may potentiate anticoagulant therapy by reducing absorption of vitamin K from the gut. It may also inhibit absorption of dextrose from the intestines.

This cathartic may increase intestinal transit time of digitalis glycosides, inhibit their absorption and cardiac action. But cathartic-induced hypokalmia increases toxicity and potency of absorbed digitalis. Cathartic-induced hypokalemia potentiates muscle relaxants. In addition to the specific interactions listed, the cathartic action of blue flag tends to hasten the passage of all oral medications through the gut and thereby inhibit their action.

In sub-laxative and sub-emetic doses this herb should have no drug interactions. At higher doses, interactions similar to those involving diuretics and cathartics may occur.

Possible Interactions
In conjunction with ACTH or corticosteroids, this diuretic is more prone to produce hypokalemia.

The use of diuretics may require dosage adjustments of antidiabetic drugs. The diuretic action of this herb may reduce renal clearance of lithium. An initial dose of captopril (an antihypertensive) may cause a severe drop in blood pressure within three hours if the person is also using a strong diuretic.

Laxative-induced diarrhea may result in decreased absorption of isoniazid the same is true with sulfisoxazole, but it appears to be a clinically unimportant interaction effect.

The antiinflammatory activity of this herb can be seriously inhibited by phenobarbital and certain other sedatives and hypnotics (chloral hydrate, meprobamate, etc.), as well as beta-adrenergic blocking agents (propanolol). Colchicine may increase sensitivity or enhance the response to this herb.

Prolonged use of this diuretic may affect certain lab test results such as electrolytes (esp. potassium and sodium), uric acid, glucose, and pbi.

Strong diuretics such as this in conjunction with indomethacin may produce natriuretic effects.

Laxative induced increased speed of intestinal emptying may result in decreased absorption of vitamin K and/or anticoagulants.

Safety Factors & Toxicity

Blue flag is said to contain an acrid, resinous substance (iridin) that can irritate the gastrointestinal tract, cause nausea and severe prostration.

Preparation & Administration

Use three times daily

Use 0.6-2g of dried rhizome

Liquid Extract
Use 1-2ml of 1:1 in 45% alcohol


Braun, H. & Frohne, D. Heilplanzen-Lexikon Fuer Aerzte und Apotheker. Gustav Fisher Verlag, Stuttgart, New York, 1987.

D'amico, M.L. Richerche sulla presenza di sostanze ad azione antibiotica nelle piante sueriori. Fitoterapia, 26(1), 77-79, 1950.

Duke, J.A. CRC Handbook of Medicinal Herbs, CRC Press, Inc., Boca Raton, Florida, 1985.

Mowrey, Daniel B., Ph.D. Exper. Psych., Brigham Young University. Director of Nebo Institute of Herbal Sciences. Director of Behavior Change Agent Training Institute. Director of Research, Nova Corp.