Blue flag was one of the most popular medicinal plants amongst various native North American Indian tribes[213]. In modern herbalism it is mainly employed to detoxify the body - it increases urination and bile production and has a mild laxative effect[254]. Some caution should be exercised in its use, however, since there are reports that it is poisonous[222]. The fresh root is quite acrid and when taken internally causes nausea, vomiting, colic and purging[4, 238]. The dried root is much less acrid[4]. This remedy should not be prescribed for pregnant women[238]. The root is alterative, anti-inflammatory, cathartic, cholagogue, diaphoretic, diuretic, emetic and sialagogue[21, 46, 165, 238]. Taken internally as a tea, the root has been used as a strong laxative or emetic that also acts strongly on the liver and promotes the excretion of excess body fluids[4, 213]. It is also stimulant for the circulatory and lymphatic system[165]. Its detoxifying effect make it useful in the treatment of psoriasis, acne, herpes, arthritis, swollen glands, pelvic inflammatory disease etc[238, 254]. Externally, it is applied to skin diseases, wounds and rheumatic joints[238]. The roots are harvested in late summer and early autumn and are usually dried for later use[4, 238]. The roots were boiled in water and then mashed to make a poultice which was used to relieve the pain and swelling associated with sores and bruises[213].