The tea form is unlikely to be effective, since the active compounds in blue flag are not water soluble. Blue flag, in excessive amounts, can cause nausea, vomiting, and loose stools if too much is taken. 5 People should not exceed the recommended amount given above. Fresh rhizome should only be applied topically and never taken internally, since it can irritate the mouth 6 and is much more likely to cause nausea and diarrhea . Blue flag should only be taken on the advice of a physician or herbalist trained in its use.
Blue flag is unsafe for use during pregnancy or lactation.
People should not give blue flag to children. Use of blue flag as a cathartic laxative is not recommended. At the time of writing, there were no well-known drug interactions with blue flag. For the convenience of the reader, the information in the table listing the supplements for particular conditions is also categorized. Ellingwood F. American Materia Medica, Therapeutics and Pharmacognosy , 11th ed.