Drug & supplement interaction

Blue Cohosh + Levothyroxine

Levothyroxine brand names: Euthyrox, Levothroid, Unithroid, Synthroid, Levoxyl, and others.

No Known Interaction
Medically reviewed by · Updated July 2026 · Pair last verified Sep 13, 2026
The bottom line No known interaction

We found no known interaction between Blue Cohosh and Levothyroxine in our sources. Absence of a documented interaction is not the same as proven safety, and does not guarantee one does not exist. Do not start, stop, or change a medication or supplement based on this page; confirm with your pharmacist or doctor first. Additionally, although there is no interaction, the label for Levothyroxine states a food rule worth keeping to, and the two are separately associated with some of the same side effects, which would make a new symptom harder to attribute to one or the other.

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Interaction report

Blue Cohosh and Levothyroxine

We checked these two against our interaction database. Here is what we found.

No Known Interaction Found

We did not find a documented interaction between Levothyroxine and Blue Cohosh in our sources. This does not guarantee that the combination is completely free of risk — there is often limited research on supplements and herbal products, especially around drug interactions.

If you decide to take both, the practical routine is simple: add one new thing at a time and note the date you started it. If the combination is going to disagree with you, it usually shows in the first days to a couple of weeks — and a start date turns “I’ve been feeling off” into something a pharmacist can actually work with. Do not stop a prescribed medicine on your own.

Always talk with your pharmacist or doctor before making changes to your medications or supplements, particularly if you take several medications or have an ongoing health condition.

Blue Cohosh safety at a glance

Blue Cohosh overall Use caution Blue cohosh contains compounds that can affect the heart and has been linked to serious adverse events.
Pregnancy Likely Unsafe When used orally. Blue cohosh is a uterine stimulant and can induce labor. Several blue cohosh constituents, such as anagyrine and N-methylcytisine, are potenti... Read the full pregnancy detail
Breastfeeding Likely Unsafe When used orally. Blue cohosh is a uterine stimulant and can induce labor. Several blue cohosh constituents, such as anagyrine and N-methylcytisine, are potenti... Read the full breastfeeding detail

Pregnancy & breastfeeding ratings are from Natural Medicines (Therapeutic Research Center) — the full detail is in the Special populations card below. Safety guidance is general; always confirm with your pharmacist or doctor for your situation.

Still wondering about combining Levothyroxine and Blue Cohosh? Ask Dr. Brian Staiger, PharmD, BCPS directly ›
How we checked

Why No Interaction Is Listed for Levothyroxine

Interactions in our licensed database are recorded against drug classes, not just single drug names. Levothyroxine is filed under 3 classifications — including thyroid hormone, oral drugs. Blue Cohosh has documented interactions with 3 drug classes — the most serious being antidiabetes drugs (moderate), antihypertensive drugs (moderate) and nicotine (moderate) — and none of Levothyroxine’s classifications are among them.

Classification data comes from our licensed Natural Medicines dataset. A medication can belong to classes beyond those recorded there, so this describes how the check was run — it is not a safety guarantee.

Keep it in perspective

Blue Cohosh Does Interact With Other Medications

Blue Cohosh has 259 moderate known drug interactions in our database — Levothyroxine isn’t one of them. If you take anything else, check it against the full list below.

Moderate 259 No known interaction 2,571 (incl. Levothyroxine)
Taking anything else?

Check Another of Your Medications Against Blue Cohosh

Covers the 2,830 medications we’ve checked against Blue Cohosh. Pick one to open its full report.

What to actually watch for

No Interaction Found — But Data Suggests Blue Cohosh and Levothyroxine May Share Several of the Same Side Effects

This is not an interaction. Neither one changes how your body handles the other, and nothing here says they react together. What our sources do show is that each has separately been linked to the effects below — so taking both can make those effects more likely to turn up, and harder to pin on one or the other if they do. 5 of them are worth acting on rather than waiting out — marked below.

  • A heart attack / Heart failure / Chest pain Worth acting on Additional detail

    Blue Cohosh

    “Orally, blue cohosh can cause significant adverse effects including mucous membrane irritation, stomach upset including diarrhea and cramping, chest pain (angina), hypertension, and hyperglycemia.

    Neonatal acute myocardial infarction (MI), congestive heart failure (CHF), and shock has occurred following maternal use of a blue cohosh combination product one month before delivery.”

    Blue Cohosh · Natural Medicines adverse-effect record, reported in abortion.

    6 sources cited
    1. 6002. Fetrow CW, Avila JR. Professional's Handbook of Complementary & Alternative Medicines. 1st ed. Springhouse, PA: Springhouse Corp., 1999.
    2. 566. Jones TK, Lawson BM. Profound neonatal congestive heart failure caused by maternal consumption of blue cohosh herbal medication. J Pediatr 1998;132:550-2. PubMed
    3. 3383. Edmunds J. Blue cohosh and newborn myocardial infarction? Midwifery Today Int Midwife 1999;52:34-5.
    4. 94534. Dugoua JJ, Perri D, Seely D, et al. Safety and efficacy of blue cohosh (Caulophyllum thalictroides) during pregnancy and lactation. Can J Clin Pharmacol. 2008;15(1):e66-73.
    5. 1122. McFarlin BL, Gibson MH, O'Rear J, Harman P. A national survey of herbal preparation use by nurse-midwives for labor stimulation. Review of the literature and recommendations for practice. J Nurse Midwifery 1999;44:205-16. PubMed
    6. 9492. Gunn TR, Wright IM. The use of black and blue cohosh in labour. N Z Med J 1996;109:410-1.

    “Orally, blue cohosh can cause tachycardia, hypertension, and chest pain (angina). Neonatal acute myocardial infarction (MI), congestive heart failure (CHF), myocardial toxicity, and shock has occurred following maternal use of a blue cohosh combination product one month before delivery.”

    Blue Cohosh · Natural Medicines adverse-effect record, reported in angina.

    6 sources cited
    1. 36720. Rao, R. B. and Hoffman, R. S. Nicotinic toxicity from tincture of blue cohosh (Caulophyllum thalictroides) used as an abortifacient. Vet.Hum.Toxicol. 2002;44(4):221-222.
    2. 36724. Scott, C. C. and Chen, K. K. The pharmacological action of N-methylcytisine. The Journal of Pharmacology and Experimental Therapuetics 1943;79:334-339. DOI
    3. 94934. Sirtori CR, Triolo M, Bosisio R, et al. Hypocholesterolaemic effects of lupin protein and pea protein/fibre combinations in moderately hypercholesterolaemic individuals. Br J Nutr 2012;107:1176-83. PubMed
    4. 566. Jones TK, Lawson BM. Profound neonatal congestive heart failure caused by maternal consumption of blue cohosh herbal medication. J Pediatr 1998;132:550-2. PubMed
    5. 3383. Edmunds J. Blue cohosh and newborn myocardial infarction? Midwifery Today Int Midwife 1999;52:34-5.
    6. 12047. Finkel RS, Zarlengo KM. Blue cohosh and perinatal stroke. N Engl J Med 2004;351:302-3. PubMed

    Levothyroxine

    Listed in the ADVERSE REACTIONS section of the FDA label for Levothyroxine. Read the label on DailyMed ›

  • Seizures Worth acting on Additional detail

    Blue Cohosh

    “In one case, a mother was advised to drink a blue cohosh tea to induce labor. The infant experienced a seizure during delivery and 2 days later it was discovered that the infant was experiencing an evolving ischemic stroke. There is also another case report of severe complications, including seizures, in an infant whose mother was given an unknown dose of black and blue cohosh at 42 weeks gestation to induce labor.”

    Blue Cohosh · Natural Medicines adverse-effect record, reported in epilepsy.

    5 sources cited
    1. 12047. Finkel RS, Zarlengo KM. Blue cohosh and perinatal stroke. N Engl J Med 2004;351:302-3. PubMed
    2. 94534. Dugoua JJ, Perri D, Seely D, et al. Safety and efficacy of blue cohosh (Caulophyllum thalictroides) during pregnancy and lactation. Can J Clin Pharmacol. 2008;15(1):e66-73.
    3. 1122. McFarlin BL, Gibson MH, O'Rear J, Harman P. A national survey of herbal preparation use by nurse-midwives for labor stimulation. Review of the literature and recommendations for practice. J Nurse Midwifery 1999;44:205-16. PubMed
    4. 9492. Gunn TR, Wright IM. The use of black and blue cohosh in labour. N Z Med J 1996;109:410-1.
    5. 94934. Sirtori CR, Triolo M, Bosisio R, et al. Hypocholesterolaemic effects of lupin protein and pea protein/fibre combinations in moderately hypercholesterolaemic individuals. Br J Nutr 2012;107:1176-83. PubMed

    Levothyroxine

    Listed in the ADVERSE REACTIONS section of the FDA label for Levothyroxine. Read the label on DailyMed ›

  • Shortness of breath Worth acting on Additional detail

    Blue Cohosh

    Recorded for Blue Cohosh in the same Natural Medicines adverse-effect record shown under A heart attack / Heart failure / Chest pain above.

    Levothyroxine

    Listed in the ADVERSE REACTIONS section of the FDA label for Levothyroxine. Read the label on DailyMed ›

  • Sweating Additional detail

    Blue Cohosh

    Recorded for Blue Cohosh in the same Natural Medicines adverse-effect record shown under A heart attack / Heart failure / Chest pain above.

    Levothyroxine

    Listed in the ADVERSE REACTIONS section of the FDA label for Levothyroxine. Read the label on DailyMed ›

  • A fast or pounding heartbeat Additional detail

    Blue Cohosh

    Recorded for Blue Cohosh in the same Natural Medicines adverse-effect record shown under A heart attack / Heart failure / Chest pain above.

    Levothyroxine

    Listed in the ADVERSE REACTIONS section of the FDA label for Levothyroxine. Read the label on DailyMed ›

  • Stomach pain / Diarrhea / Vomiting Additional detail

    Blue Cohosh

    “Orally, blue cohosh can cause mucous membrane irritation, stomach upset including diarrhea and cramping, nausea, vomiting, and abdominal pain.”

    Blue Cohosh · Natural Medicines adverse-effect record, reported in diarrhea.

    1 source cited
    1. 36720. Rao, R. B. and Hoffman, R. S. Nicotinic toxicity from tincture of blue cohosh (Caulophyllum thalictroides) used as an abortifacient. Vet.Hum.Toxicol. 2002;44(4):221-222.

    Levothyroxine

    Listed in the ADVERSE REACTIONS section of the FDA label for Levothyroxine. Read the label on DailyMed ›

Showing the 10 most notable of 11 shared effects — ranked by how unusual each one is, not just whether both lists mention it.

Reported for Blue Cohosh but not commonly for Levothyroxine: muscle pain, a stroke or mini-stroke, stomach upset and high blood sugar.

Effects for Levothyroxine come from the ADVERSE REACTIONS section of its FDA label; effects for Blue Cohosh come from the Natural Medicines adverse-effect record, quoted above. Wording is matched across sources by our own clinical vocabulary, so treat this as a prompt to pay attention, not a diagnosis.

Special populations

Blue Cohosh in Pregnancy & Breastfeeding

Pregnancy And Lactation Likely Unsafe

When used orally. Blue cohosh is a uterine stimulant and can induce labor. Several blue cohosh constituents, such as anagyrine and N-methylcytisine, are potentially teratogenic and might cause congenital malformations in newborns. Use of blue cohosh near term can cause life-threatening toxicity in the infant, as well as severe toxicity in the mother. Many midwives still use blue cohosh to facilitate delivery. This dangerous practice should be avoided.

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.© 2026 Therapeutic Research Center

How to take them

Some Levothyroxine Products Have a Food Rule — Blue Cohosh Should Not Break It

At least one FDA label for a product containing Levothyroxine says to take it on an empty stomach. Most supplements — Blue Cohosh included — are taken with a meal, so the easy mistake is swallowing both together at breakfast. Where that rule applies, keep Levothyroxine on its own and move Blue Cohosh to a meal later in the day.

This may not be true of your version. Food instructions belong to the product, not the ingredient: two Levothyroxine products can carry different directions, and extended-release forms often differ from immediate-release ones. The label we read is quoted below — check the directions on your own box or bottle, or ask your pharmacist, for how to take the exact product you were given.

A food rule is not an interaction — it is about how much of the medicine you absorb. The directions that came with your own product, and your pharmacist, outrank anything on this page.

From our Q&A

Questions About Blue Cohosh or Levothyroxine

These are real questions from readers, answered by the pharmacists at HelloPharmacist — written by a person, not generated from a database. Each one covers Blue Cohosh or Levothyroxine, not necessarily both, but if one is close to what you were about to ask it will usually go further than a database entry can:

Not quite your question? Ask our pharmacists directly — it is free, there is no account required, and answers usually come back within 24 hours.

Everything else you take

See Every Supplement That Interacts With Levothyroxine

This page covers Blue Cohosh only. If you take other supplements — a multivitamin, a sleep aid, something for joints — the Levothyroxine page lists 50 supplements it has a documented interaction with, worst first, each one explained.

The most serious there right now: Activated Charcoal (major), Tiratricol (major), Acetyl-l-carnitine (moderate), Alpha-lipoic Acid (moderate) and Ascophyllum Nodosum (moderate).

By severity: 2 major · 39 moderate · 9 minor.

From our pharmacist’s overview on the Levothyroxine page

“Levothyroxine replaces a hormone your body measures in tiny amounts, so small shifts in its blood level show up in how you feel, and I treat this list with genuine care. Nearly everything on it does one of two things: blocks the pill from being absorbed in the gut, the way everyday minerals like calcium do by binding it into complexes,…”

Reviewed by 2 · Jul 18, 2026

Open the Levothyroxine interaction page

One more smart check

Taking Blue Cohosh as Part of a Dietary Supplement Product? Check It for Interactions

We hold 126 real supplement products containing Blue Cohosh, each one broken down to its full ingredient list — and combination products often carry several ingredients besides Blue Cohosh. Even though Blue Cohosh itself has no known interaction with Levothyroxine, another ingredient on your label might. Find your product and we’ll check every ingredient on its label:

How much people look this up

Where Blue Cohosh and Levothyroxine Sit Against Everything Else

Out of every supplement and medication people look up on HelloPharmacist, here is where these two land this week — and which way each has been moving.

Supplement Blue Cohosh
Steady interest

#1,083 of 1,452 supplements looked up here in the last 7 days

29 days ago today
Medication Levothyroxine
Top 10

#2 of 2,830 medications looked up here in the last 7 days

29 days ago today

Position among everything looked up on this site, not a measure of how commonly either one is used or how important it is. A supplement can climb this list because of a news story. It counts every request to the page, automated ones included, and nothing here identifies anyone.

Where does our data come from?
  • Source: the Natural Medicines (TRC Healthcare) clinical database — the evidence-graded professional reference for herb & supplement interactions.
  • Citation library: 103,510 references behind our interaction content, 65,311 of them resolved to verified PubMed/DOI sources. See every Blue Cohosh reference on this page ↓
  • Freshness: we automatically re-check this combination every week — this pair was last verified September 13, 2026. The Blue Cohosh and Levothyroxine records this page draws on were last updated July 10, 2026.
  • What “no known interaction” means: no documented interaction in the sources above — not a guarantee of safety. Supplements are studied far less than prescription drugs, so we say exactly what the evidence supports, and nothing more.
Data structure & sourcing designed and verified by .
Supplement

About Blue Cohosh

What is Blue Cohosh?

  • Inducing labor or starting menstruation
  • Menstrual cramps and irregular periods
  • Symptoms of menopause
  • Pelvic or uterine discomfort
  • Traditional Native American remedy

Blue cohosh is a traditional herb historically used by Native Americans and midwives to bring on labor or menstruation, but it carries serious safety concerns, especially for the heart and during pregnancy. There is very little reliable human evidence that it works, and reports of harm—including serious problems in newborns—make it an herb most people should avoid without close professional supervision.

Caulophyllum thalictroides · Berberidaceae · Root and rhizome · Capsules, tinctures, dried root, tea, liquid extracts

An interaction check asks whether these two react with each other — it does not ask whether Blue Cohosh is a good idea for someone in your situation. Here is what our Blue Cohosh record says about it on its own.

Blue Cohosh: dosing

There is no well-established, standardized safe dose for blue cohosh. Products vary widely in strength, and the herb's safety concerns make general dosing recommendations inappropriate.Because of the risk of serious side effects, we do not provide specific amounts.

From our Blue Cohosh monograph — the full record covers uses, side effects and every documented interaction.

Read the full Blue Cohosh monograph & all interactions
Medication

About Levothyroxine

What Is Levothyroxine Used For?

Brand names: Euthyrox, Levothroid, Unithroid, Synthroid, Levoxyl, Levo-T, Eltroxin, Estre, Levothyroxine, Novothyrox, Levolet

Levothyroxine replaces or supplements the thyroid hormone your body isn't making enough of. It's used for hypothyroidism — an underactive thyroid — in adults, children, and even newborns, whether the cause is the thyroid gland itself, the pituitary gland, or the hypothalamus in the brain.

It's also used alongside surgery and radioiodine treatment in people with certain types of thyroid cancer, to help suppress the hormone that can stimulate cancer growth. It is not meant for weight loss, treating benign thyroid nodules in people who have enough iodine, or for hypothyroidism during recovery from a temporary condition called subacute thyroiditis.

See full Levothyroxine drug information
Keep checking

Other Drugs & Blue Cohosh

Browse every other medication we’ve checked against Blue Cohosh — both the ones with a known interaction and the ones without. Select any drug for the full detail.

0Major
259Moderate
0Minor
2,570No known interaction
259 Moderate 2,570 No interaction
Moderate

259 interactions

Showing 60 of 259 moderate interactions — see all 259 on the Blue Cohosh page.

No interaction 2,570 drugs checked — show the list

We also checked Blue Cohosh against these medications and found no known interaction in our sources. Open any page to confirm.

Showing the 60 most looked-up of 2,570 medications checked with no known interaction — see the full Blue Cohosh list.

See the full Blue Cohosh interactions page
See every supplement checked against Levothyroxine, ranked by severity
Evidence & sources

Blue Cohosh References

The 16 references that drive our Blue Cohosh 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.

  1. Jones TK, Lawson BM. Profound neonatal congestive heart failure caused by maternal consumption of blue cohosh herbal medication. J Pediatr 1998;132:550-2. PubMed
  2. McFarlin BL, Gibson MH, O'Rear J, Harman P. A national survey of herbal preparation use by nurse-midwives for labor stimulation. Review of the literature and recommendations for practice. J Nurse Midwifery 1999;44:205-16. PubMed
  3. Wright IM. Neonatal effects of maternal consumption of blue cohosh. J Pediatr 1999;134:384-5. DOI
  4. Edmunds J. Blue cohosh and newborn myocardial infarction? Midwifery Today Int Midwife 1999;52:34-5.
  5. Fetrow CW, Avila JR. Professional's Handbook of Complementary & Alternative Medicines. 1st ed. Springhouse, PA: Springhouse Corp., 1999.
  6. Irikura B, Kennelly E. American Health Consultants. Blue Cohosh: a word of caution. 1999. Available at: http://www.ahcmedia.com/articles/50424-blue-cohosh-a-word-of-caution.
  7. Gunn TR, Wright IM. The use of black and blue cohosh in labour. N Z Med J 1996;109:410-1.
  8. Baillie N, Rasmussen P. Black and blue cohosh in labour. N Z Med J 1997;110:20-1.
  9. Finkel RS, Zarlengo KM. Blue cohosh and perinatal stroke. N Engl J Med 2004;351:302-3. PubMed
  10. Kennelly, E. J., Flynn, T. J., Mazzola, E. P., Roach, J. A., McCloud, T. G., Danford, D. E., and Betz, J. M. Detecting potential teratogenic alkaloids from blue cohosh rhizomes using an in vitro rat embryo culture. J.Nat.Prod. 1999;62(10):1385-1389. PubMed
  11. Rao, R. B. and Hoffman, R. S. Nicotinic toxicity from tincture of blue cohosh (Caulophyllum thalictroides) used as an abortifacient. Vet.Hum.Toxicol. 2002;44(4):221-222.
  12. Gunn, T. R. and Wright, I. M. The use of black and blue cohosh in labour. N.Z Med J 10-25-1996;109(1032):410-411.
  13. Scott, C. C. and Chen, K. K. The pharmacological action of N-methylcytisine. The Journal of Pharmacology and Experimental Therapuetics 1943;79:334-339. DOI
  14. Low, D. T. Blue cohosh and neonatal myocardial toxicity. Journal of the American Herbalists Guild 2001;2(2):9-10.
  15. Dugoua JJ, Perri D, Seely D, et al. Safety and efficacy of blue cohosh (Caulophyllum thalictroides) during pregnancy and lactation. Can J Clin Pharmacol. 2008;15(1):e66-73.

Medication overviews come from MedlinePlus (NIH); supplement label data from the NIH Dietary Supplement Label Database. Content is written and reviewed by licensed HelloPharmacist pharmacists — see our data sources and editorial standards.

Pharmacist Counseling Corner

Taking Blue Cohosh and Levothyroxine Together: Common Questions

Is it safe to take Blue Cohosh with Levothyroxine?
We do not list a known interaction between Blue Cohosh and Levothyroxine. That does not guarantee the combination is risk-free, so confirm with your pharmacist or doctor — especially if you take other medications or have a health condition.
Do Blue Cohosh and Levothyroxine have any of the same side effects?
Yes — our sources link each of them separately to 10 of the same effects. That is not an interaction: neither changes how your body handles the other. It does mean that if one of those effects turns up, it can be harder to tell which one is behind it. They are listed on this page with the source behind each.
Should I take Blue Cohosh and Levothyroxine at the same time of day?
At least one FDA label for a product containing Levothyroxine says to take it on an empty stomach, and supplements are usually taken with a meal — so taking them together at breakfast is the easy mistake. Where that applies, keep Levothyroxine on its own and move Blue Cohosh to a meal later in the day. Food instructions belong to the product rather than the ingredient, so check the directions on your own box. This is about absorption, not an interaction.
How was the Blue Cohosh and Levothyroxine combination checked?
Interactions in our licensed database are recorded against drug classes. Levothyroxine is filed under 3 classifications, and Blue Cohosh has documented interactions with 3 drug classes — none of Levothyroxine's classifications are among them. A medication can belong to classes beyond those recorded in our dataset, so this describes how the check was run rather than guaranteeing safety.
Does Blue Cohosh interact with any other medications?
Yes. Blue Cohosh has 259 documented drug interactions in our database — Levothyroxine is simply not one of them. If you take anything else, it is worth checking each one; they are all listed on this page.
Does Levothyroxine interact with any supplements?
Yes. Levothyroxine has documented interactions with 50 supplements in our database — Blue Cohosh is not one of them. The Levothyroxine interaction page linked on this page lists every one, ranked by severity.

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

Where next

Keep Exploring

Blue Cohosh monograph Uses, safety profile, and every drug interaction in one place Levothyroxine drug information The full plain-English guide to this medication Levothyroxine supplement interactions Every supplement checked against Levothyroxine, ranked by severity Supplement interaction checker Check any supplement or product against your medications Browse medications A–Z Every drug we’ve checked against herbs & supplements References The 16 citations behind this page Ask a pharmacist Free, personal answer from our licensed team

Still Have a Question About Levothyroxine and Blue Cohosh?

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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.