Herb & supplement monograph

Blue Flag Drug Interactions, Uses, Safety & More

Medically reviewed by Dr. Brian Staiger, PharmD, BCPS ·Updated July 2026

What is this page for?

First and foremost: how Blue Flag interacts with medications. The heart of this page is the interaction list — every drug Blue Flag is known to interact with, and how serious each one is.

But these pages have grown well beyond that into a full monograph — what Blue Flag is, what people use it for and how strong the evidence is, its safety and side effects, and answers to the questions we’re asked most — written and reviewed by the clinical staff at HelloPharmacist. It’s educational information from our licensed clinical databases, not medical advice, and we don’t sell or endorse products. Our editorial policy

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Blue Flag Drug Interactions: The Bottom Line

From the HelloPharmacist Editorial Team · Updated July 2026

Based on the available evidence, most Blue Flag drug interactions are moderate and largely theoretical, so the overall risk of a clinically significant problem appears modest for most people using normal amounts. Only one listed interaction is rated major, and the concerns generally arise from overuse of the supplement rather than typical use, with limited human documentation.

Interactions deserving the most attention

The interaction that deserves the most care involves digoxin, since overusing Blue Flag may raise the risk of side effects from this narrow-margin heart medication, and this pairing has the strongest supporting evidence in the profile. Blue Flag may also add to potassium loss in people taking potassium-depleting diuretics, which could increase the chance of low potassium. In people taking warfarin, the plant's laxative effect can cause diarrhea, which may raise INR and bleeding risk if large amounts are used.

What the rest of the list means

Although the full list of interacting medications is long, that does not mean every combination is harmful. Most of these concerns are moderate, rest on limited evidence, and trace back to the same few effects, mainly potassium loss and a laxative action that show up chiefly with overuse rather than ordinary amounts.

Check your medications against Blue Flag

Based on HelloPharmacist’s Blue Flag interaction data and reviewed under our editorial standards.

Interaction report

Drugs that interact with Blue Flag

78 medications have a known interaction with Blue Flag, graded by severity. Select any drug for the full evidence-based detail.

1 major interaction. These combinations can be clinically significant — best avoided, or used only with close professional supervision. Always check with your pharmacist before combining them with Blue Flag.

Don’t want to scroll the list? Just ask.

Tell us the medications you take and we’ll check each one against Blue Flag using our pharmacist-reviewed interaction data.

AI summaries are generated from our Blue Flag interaction data for education only — always confirm with your pharmacist. How we use AI

2,830 drugs

Read The List Like a Pharmacist

What Severity, Likelihood & Evidence Mean

Severity — How Serious It Can Be

Major. Clinically significant; generally best avoided, or used only under direct professional supervision.
Moderate. May need monitoring, a dose adjustment, or separating the times you take each one.
Minor. Generally not clinically significant, but still worth noting and mentioning to your pharmacist.
No known interaction. Checked against our sources with nothing documented — not the same as proven safety.

Likelihood — How Well It’s Documented

Likely. Well-controlled human studies have demonstrated the likely existence of this interaction
Probable. Interaction has not been documented in well-controlled studies, however, the interaction has been demonstrated in some small human studies or in controlled animal studies in conjunction with multiple case reports.
Possible. Interaction has been documented in animal or in lab research, or the interaction has been documented in humans but is limited to case reports or conflicting clinical research exists
Unlikely. Interaction has been demonstrated in animal or in lab research but has been shown not to occur in humans.

Where This Data Comes From

Interaction records are evidence-graded and sourced from the Natural Medicines database (TRC Healthcare), the same reference used by pharmacists and hospitals.
Each drug listed above links to the full report for that exact Blue Flag combination — clinical detail, likelihood, evidence level, and citations.
Content is reviewed by licensed HelloPharmacist pharmacists — see our data sources and editorial standards.

The big picture

The kinds of drugs Blue Flag affects

Every type of medication (drug category) Blue Flag is known to interact with. Open any category for the detail — or search your exact drug in the checker above.

All 3 drug categories Blue Flag interacts with

Digoxin (lanoxin)Diuretic DrugsWarfarin (coumadin)

Digoxin (Lanoxin)

Theoretically, overuse or abuse of this product increases the risk of adverse effects from cardiac glycoside drugs.

Likelihood Probable Evidence D

Diuretic Drugs

Overuse of blue flag might compound diuretic-induced potassium loss. There is some concern that people taking blue flag along with potassium depleting diuretics might have an increased risk for hypokalemia. Initiation of potassium supplementation or an increase in potassium supplement dose may be necessary for some patients. Some diuretics that can deplete potassium include chlorothiazide (Diuril), chlorthalidone (Thalitone), furosemide (Lasix), hydrochlorothiazide (HCTZ, Hydrodiuril, Microzide), and others.

Likelihood Possible Evidence D

Warfarin (Coumadin)

Blue flag has stimulant laxative effects. In some people blue flag can cause diarrhea. Diarrhea can increase the effects of warfarin, increase international normalized ratio (INR), and increase the risk of bleeding. Advise patients who take warfarin not to take excessive amounts of blue flag.

Likelihood Possible Evidence D

Monograph

Blue Flag: Uses, Safety & Side Effects

Medically reviewed by Dr. Brian Staiger, PharmD, BCPS · Reviewed July 2026 ·

The bottom line

Blue Flag is a flowering plant whose root has been used in traditional and herbal medicine for skin and digestive complaints, but there is very little modern scientific evidence to support these uses. The fresh root can be toxic and irritating, so it should be used cautiously, if at all, and avoided in pregnancy and breastfeeding. Talk to a pharmacist or doctor before trying it.

Scientific name: Iris versicolor
Family: Iridaceae
Part used: Dried rhizome (root)
Common forms: Dried root, tincture, liquid extract, capsules, occasionally in topical preparations

People commonly use it for

Skin conditions like acne and eczema
Constipation and digestive complaints
Liver and gallbladder support (traditional)
Lymphatic and 'detox' tonic (traditional)
Thyroid and glandular swelling (traditional)

Popular and traditional uses — not proof it works. See “Uses & effectiveness” below for the evidence.

Safety at a glance

OverallUse caution

The root, especially when fresh, can cause nausea, vomiting, and irritation, so it should be used cautiously.

PregnancyBest avoided

Avoid during pregnancy because of potential toxicity and lack of safety data.

BreastfeedingLikely Unsafe

When used orally; avoid using.

Read the full breastfeeding detail

Pregnancy & breastfeeding ratings are from Natural Medicines (Therapeutic Research Center). Safety guidance is general; always confirm with your pharmacist or doctor for your situation.

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Overview

Blue Flag (Iris versicolor) is a flowering plant in the iris family. It grows in wet meadows, marshes, and along stream banks across North America, producing showy blue-purple flowers. The part used in herbal medicine is the dried underground stem, called the rhizome or root.

Historically, Blue Flag root was used by Native American peoples and later by herbalists for skin problems, sluggish digestion, and as a 'blood purifier' or 'detox' remedy. Today it is sometimes found in tinctures, dried root preparations, and herbal blends, but it is far less common than many other herbs.

Uses & effectiveness

People have traditionally used Blue Flag for skin conditions such as acne and eczema, for constipation, and as a general 'cleansing' tonic for the liver, gallbladder, and lymph system. Some traditional uses also include glandular swelling and thyroid complaints.

It is important to be honest: there is very little modern scientific evidence to show that Blue Flag works for any of these conditions. Most claims come from traditional use and old herbal texts rather than well-designed human studies. Because of this, Blue Flag should not be relied on to treat any medical condition.

How it works

Blue Flag root contains compounds such as resins, oils, and other plant chemicals that may irritate the gut and stimulate the digestive system, which is thought to be why it was traditionally used as a laxative and 'cleanser.'

The exact way it might affect the skin, liver, or lymph system is not well understood, and proposed mechanisms are based mostly on tradition and limited laboratory observations rather than solid human research. There is not enough scientific data to confirm any specific active ingredient or how it works in the body.

Safety & precautions

Blue Flag should be used with caution. The fresh root is considered toxic and can cause strong irritation of the mouth, throat, and stomach. Drying the root reduces but does not fully remove this risk. Handling the fresh plant may also irritate the skin.

People with digestive conditions, those who are sensitive to laxatives, children, and older adults should be especially careful. Because of its potential toxicity and lack of safety data, pregnant women should avoid Blue Flag, and it should also be avoided while breastfeeding. Always check with a pharmacist or doctor before using it.

Side effects

The most commonly reported side effects involve the digestive system, including nausea, vomiting, stomach cramps, and diarrhea, especially at higher doses or when fresh root is used. Burning of the mouth and throat can also occur.

In larger amounts, Blue Flag may cause more serious effects. Skin contact with the fresh plant can lead to irritation. If you notice severe vomiting, abdominal pain, or any concerning reaction, stop using it and seek medical care.

Blue Flag: Reported Adverse Effects

Documented safety reports on Blue Flag from the evidence-graded Natural Medicines (TRC Healthcare) database, shown word-for-word from the licensed record.

Orally, blue flag can cause nausea and vomiting, and the fresh root can irritate mucosa. Orally and topically, the volatile oil constituent of blue flag irritates mucous membranes and can cause lacrimation, eye inflammation, irritation of the throat, and headache.

Newall CA, Anderson LA, Philpson JD. Herbal Medicine: A Guide for Healthcare Professionals. London, UK: The Pharmaceutical Press, 1996.
Brinker F. Herb Contraindications and Drug Interactions. 2nd ed. Sandy, OR: Eclectic Medical Publications, 1998.

Reports by condition

Cluster headache Neurologic/CNS

Orally, the volatile oil constituent of blue flag can cause headache.

Newall CA, Anderson LA, Philpson JD. Herbal Medicine: A Guide for Healthcare Professionals. London, UK: The Pharmaceutical Press, 1996.

Nausea and vomiting Gastrointestinal

Orally, blue flag can cause nausea and vomiting and the fresh blue flag root can irritate mucosa. The volatile oil constituent of blue flag irritates mucous membranes and can cause irritation of the throat.

Newall CA, Anderson LA, Philpson JD. Herbal Medicine: A Guide for Healthcare Professionals. London, UK: The Pharmaceutical Press, 1996.
Brinker F. Herb Contraindications and Drug Interactions. 2nd ed. Sandy, OR: Eclectic Medical Publications, 1998.

DISCLAIMER: This tool is intended for informational purposes only, and should not be interpreted as specific medical advice. Patients should consult with a qualified healthcare provider before making decisions about therapies and/or health conditions.

Adverse-effects data: Natural Medicines, Therapeutic Research Center

Dosing

There is no well-established or standardized dose for Blue Flag, and reliable dosing information from quality clinical research is lacking. Traditional sources used small amounts of the dried root or tincture, but these are not validated by modern studies.

If a product is used, follow the directions on the label and start low. Because of the plant's potential for toxicity, it is best to speak with a pharmacist or doctor before taking Blue Flag and to avoid the fresh root.

Pregnancy & Breastfeeding

Blue Flag & Breastfeeding

Likely Unsafe

When used orally; avoid using.

Newall CA, Anderson LA, Philpson JD. Herbal Medicine: A Guide for Healthcare Professionals. London, UK: The Pharmaceutical Press, 1996.
McGuffin M, Hobbs C, Upton R, Goldberg A, eds. American Herbal Products Association's Botanical Safety Handbook. Boca Raton, FL: CRC Press, LLC 1997.

Pregnancy & lactation ratings: Natural Medicines, Therapeutic Research Center

References & further reading

The 3 references that drive our Blue Flag monograph and interaction data, from the evidence-graded Natural Medicines (TRC Healthcare) database. Citations with a link open the study on PubMed or the publisher’s site.

Newall CA, Anderson LA, Philpson JD. Herbal Medicine: A Guide for Healthcare Professionals. London, UK: The Pharmaceutical Press, 1996.
McGuffin M, Hobbs C, Upton R, Goldberg A, eds. American Herbal Products Association's Botanical Safety Handbook. Boca Raton, FL: CRC Press, LLC 1997.
Brinker F. Herb Contraindications and Drug Interactions. 2nd ed. Sandy, OR: Eclectic Medical Publications, 1998.

Keep reading

This information is for education only and is not a substitute for professional medical advice. Always check with your pharmacist or doctor before starting, stopping, or combining supplements and medications.

Parts of this content are provided by the Therapeutic Research Center, LLC.

DISCLAIMER: Currently this does not check for drug-drug interactions. This is not an all-inclusive comprehensive list of potential interactions and is for informational purposes only. Not all interactions are known or well-reported in the scientific literature, and new interactions are continually being reported. Input is needed from a qualified healthcare provider including a pharmacist before starting any therapy. Application of clinical judgment is necessary.

Brand directory

Brands that make products with Blue Flag

24 brands in our database make a supplement containing Blue Flag.

BareOrganics 145 products BIOVEA 1,494 products California Academy of Health 219 products Earth Friend Herb Co. 66 products Energetix 283 products Enzymatic Therapy 675 products Hawaii Pharm 4,726 products Herb Pharm 3,320 products Herbal Terra 3,138 products Herbalist & Alchemist 613 products Herbs, Etc. 388 products Nutri-West 294 products Pure Herbs 634 products Restorative Formulations 3 products RidgeCrest Herbals 67 products SurThrival 28 products TerraVita 2,475 products TerraVita Premium Collection 4,019 products Thorne Research 758 products Thymely Solutions 145 products Village Vitality 361 products VitalBulk 269 products Vitanica 94 products Wise Woman Herbals 237 products

Product directory

Supplement products with Blue Flag

101 products in our database contain Blue Flag. Open any to see its full ingredient list and every drug interaction we check.

Pharmacist Counseling Corner

Blue Flag: Common Questions

Does Blue Flag interact with prescription medications?

Yes. We list 78 medications with a known interaction with Blue Flag, including 1 rated major. Use the checker above to see how Blue Flag interacts with a specific drug.

How are Blue Flag interactions rated?

Each interaction is graded major, moderate, or minor based on how clinically significant it is and the strength of the evidence behind it. Major interactions are the most serious and are best avoided, or used only under close professional supervision.

Is it safe to take Blue Flag with my medications?

It depends on the specific medication. Some combinations are fine, while others call for monitoring, timing changes, or should be avoided. Check your exact drug above and confirm with your pharmacist or doctor before starting, stopping, or changing anything.

Where does this Blue Flag interaction information come from?

Our interaction data is built on the Natural Medicines database — an evidence-graded reference for vitamins, herbs, and supplements — and is reviewed by licensed HelloPharmacist pharmacists, who may add clinical context.

What is Blue Flag used for?

It has traditionally been used for skin problems like acne and eczema, for constipation, and as a 'detox' or cleansing tonic, but there is little scientific evidence that it works for these uses.

Is Blue Flag safe to take?

It should be used with caution. The root, especially when fresh, can be toxic and cause nausea, vomiting, and stomach upset, so check with a healthcare professional before using it.

Can I use Blue Flag during pregnancy or while breastfeeding?

No. Because of its potential toxicity and the lack of safety data, Blue Flag should be avoided during pregnancy and breastfeeding.

What are the side effects of Blue Flag?

The most common side effects are nausea, vomiting, stomach cramps, and diarrhea, and the fresh plant may irritate the mouth, throat, and skin.

Written and reviewed by the HelloPharmacist editorial staff. Our editorial policy

Keep exploring

Products that contain Blue Flag

A rotating sample of real supplements in our database that list Blue Flag — open any to see its full ingredients and every drug interaction we check.

See all 101 products with Blue Flag →

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