Drug & supplement interaction

Foxglove + Letrozole

Letrozole brand name: Femara.

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 Foxglove and Letrozole 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 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

Foxglove and Letrozole

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 Letrozole and Foxglove 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.

Foxglove safety at a glance

Foxglove overall Avoid Foxglove is poisonous and can cause fatal heart rhythm problems; it should never be self-used.
Pregnancy Unsafe When used orally for self-medication; avoid using. Read the full pregnancy detail
Breastfeeding Unsafe When used orally for self-medication; avoid using. 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 Letrozole and Foxglove? Ask Dr. Brian Staiger, PharmD, BCPS directly ›
How we checked

Why No Interaction Is Listed for Letrozole

Interactions in our licensed database are recorded against drug classes, not just single drug names. Letrozole is filed under 4 classifications — including aromatase inhibitors, cytochrome p450 2c19 (cyp2c19) inhibitors, cytochrome p450 3a4 (cyp3a4) substrates. Foxglove has documented interactions with 6 drug classes — the most serious being digoxin (lanoxin) (major), quinine (major) and diuretic drugs (moderate) — and none of Letrozole’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

Foxglove Does Interact With Other Medications

Foxglove has 3 major, 130 moderate known drug interactions in our database — Letrozole isn’t one of them. If you take anything else, check it against the full list below.

Major 3 Moderate 130 No known interaction 2,697 (incl. Letrozole)
Taking anything else?

Check Another of Your Medications Against Foxglove

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

What to actually watch for

No Interaction Found — But Data Suggests Foxglove and Letrozole 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.

  • Tiredness / Dizziness Additional detail

    Foxglove

    “Orally, acute poisoning of foxglove includes symptoms of dizziness, stupor, confusion, convulsions, fatigue and sometimes vision disturbances (6,159,501,102790,105852). Chronic use of foxglove can lead to intoxication symptoms including visual halos and yellow-green vision (6).”

    Foxglove · Natural Medicines adverse-effect record, reported in fatigue.

    5 sources cited
    1. 6. The Review of Natural Products by Facts and Comparisons. St. Louis, MO: Wolters Kluwer Co., 1999.
    2. 159. Gossel TA, Bricker JD. Principles of Clinical Toxicology. New York, NY:Raven Press, 1994.
    3. 501. De Smet PAGM, Keller K, Hansel R, Chandler RF, Eds. Adverse Effects of Herbal Drugs 1. Verlag, Berlin: Springer, 1992. DOI
    4. 102790. Negroni MS, Marengo A, Caruso D, et al. A case report of accidental intoxication following ingestion of foxglove confused with borage: High digoxinemia without major complications. Case Rep Cardiol. 2019;2019:9707428. PubMed
    5. 105852. Rouault E, Ghnassia C, Filippi-Codaccioni E, Maillard N. Dose and efficacy of repeated administrations of digoxin-specific antibody fragments: Case report of foxglove poisoning. Basic Clin Pharmacol Toxicol 2021;128(1):183-186. PubMed

    Letrozole

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

  • Nausea Additional detail

    Foxglove

    “Orally, acute poisoning of foxglove includes nausea, vomiting, and gastrointestinal (GI) upset (6,159,501,102790,102791,105851,105852). Chronic use of foxglove can also lead to intoxication symptoms including GI upset (6).”

    Foxglove · Natural Medicines adverse-effect record, reported in nausea and vomiting.

    6 sources cited
    1. 6. The Review of Natural Products by Facts and Comparisons. St. Louis, MO: Wolters Kluwer Co., 1999.
    2. 159. Gossel TA, Bricker JD. Principles of Clinical Toxicology. New York, NY:Raven Press, 1994.
    3. 501. De Smet PAGM, Keller K, Hansel R, Chandler RF, Eds. Adverse Effects of Herbal Drugs 1. Verlag, Berlin: Springer, 1992. DOI
    4. 102790. Negroni MS, Marengo A, Caruso D, et al. A case report of accidental intoxication following ingestion of foxglove confused with borage: High digoxinemia without major complications. Case Rep Cardiol. 2019;2019:9707428. PubMed
    5. 102791. Maes KR, Depuydt P, Vermassen J, De Paepe P, Buylaert W, Lyphout C. Foxglove poisoning: diagnostic and therapeutic differences with medicinal digitalis glycosides overdose. Acta Clin Belg. 2020:1-7. PubMed
    6. 105851. Lehmann A, Späni S, Harings-Kaim A, Probst C, Christ A, Leuppi-Taegtmeyer AB. A case of intoxication with tea made from Digitalis purpurea. Glob Cardiol Sci Pract 2021;2021(1):e202102. PubMed

    Letrozole

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

Reported for Foxglove but not commonly for Letrozole: an electrolyte imbalance, muscle weakness, blurred vision and seizures.

Effects for Letrozole come from the ADVERSE REACTIONS section of its FDA label; effects for Foxglove 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

Foxglove in Pregnancy & Breastfeeding

Pregnancy And Lactation Unsafe

When used orally for self-medication; avoid using.

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

From our Q&A

Questions About Foxglove or Letrozole

These are real questions from readers, answered by the pharmacists at HelloPharmacist — written by a person, not generated from a database. Each one covers Foxglove or Letrozole, 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 Letrozole

This page covers Foxglove only. If you take other supplements — a multivitamin, a sleep aid, something for joints — the Letrozole page lists 142 supplements it has a documented interaction with, worst first, each one explained.

The most serious there right now: Activated Charcoal (major), Grapefruit (major), St. John's Wort (major), 7-methoxyflavone (moderate) and Acacia Rigidula (moderate).

By severity: 3 major · 99 moderate · 40 minor.

From our pharmacist’s overview on the Letrozole page

“Letrozole (Femara) is prescribed to keep hormone-driven breast cancer from returning, so a supplement that shifts its blood level can quietly undercut treatment. Give this list of 142 ingredients genuine respect, and learn the three major entries first.”

Reviewed by 2 · Jul 18, 2026

Open the Letrozole interaction page

One more smart check

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

We hold 1 real supplement products containing Foxglove, each one broken down to its full ingredient list — and combination products often carry several ingredients besides Foxglove. Even though Foxglove itself has no known interaction with Letrozole, 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 Foxglove and Letrozole 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 Foxglove
Top half

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

29 days ago today
Medication Letrozole
Top 5%

#50 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 Foxglove reference on this page ↓
  • Freshness: we automatically re-check this combination every week — this pair was last verified September 13, 2026. The Foxglove and Letrozole 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 Foxglove

What is Foxglove?

  • Heart failure (historical/medical use)
  • Irregular heartbeat (historical/medical use)
  • Fluid retention or 'dropsy' (historical use)
  • Ornamental garden plant

Foxglove is a beautiful but highly poisonous plant that contains powerful heart-affecting compounds called cardiac glycosides. It should never be used as a home remedy or supplement because even small amounts can cause life-threatening heart problems. The purified prescription drugs derived from it (like digoxin) are used only under close medical supervision.

Digitalis purpurea · Plantaginaceae · Leaves (the dried leaf was historically the source of medicine) · Not recommended in any form; historically used as dried leaf, tincture, or purified drug (digoxin/digitoxin)

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

Foxglove: dosing

There is no safe home dose of foxglove. Because the strength of the natural plant cannot be measured reliably, it should not be taken in any amount as a supplement, tea, or tincture.If your doctor decides you need the heart medicine derived from this plant, you will receive a purified, prescription product with a precise dose and regular blood tests and monitoring.

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

Read the full Foxglove monograph & all interactions
Medication

About Letrozole

What Is Letrozole Used For?

Brand name: Femara

Letrozole (brand name Femara) is used to treat breast cancer in postmenopausal women whose tumors are driven by estrogen. It is used in three settings: as adjuvant (after-surgery) treatment for hormone receptor positive early breast cancer; as extended adjuvant treatment for women who have already completed about five years of tamoxifen therapy; and as first- or second-line treatment for locally advanced or metastatic (spread) breast cancer.

Femara is specifically indicated for first-line treatment of hormone receptor positive or receptor-unknown locally advanced or metastatic breast cancer, and for advanced breast cancer in women whose disease has progressed after antiestrogen therapy.

See full Letrozole drug information
Keep checking

Other Drugs & Foxglove

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

3Major
130Moderate
0Minor
2,696No known interaction
3 Major 130 Moderate 2,696 No interaction
Major

3 interactions

Moderate

130 interactions

Showing 60 of 130 moderate interactions — see all 130 on the Foxglove page.

No interaction 2,696 drugs checked — show the list

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

Showing the 60 most looked-up of 2,696 medications checked with no known interaction — see the full Foxglove list.

See the full Foxglove interactions page
See every supplement checked against Letrozole, ranked by severity
Evidence & sources

Foxglove References

The 19 references that drive our Foxglove 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. Blumenthal M, ed. The Complete German Commission E Monographs: Therapeutic Guide to Herbal Medicines. Trans. S. Klein. Boston, MA: American Botanical Council, 1998.
  2. The Review of Natural Products by Facts and Comparisons. St. Louis, MO: Wolters Kluwer Co., 1999.
  3. McGuffin M, Hobbs C, Upton R, Goldberg A, eds. American Herbal Products Association's Botanical Safety Handbook. Boca Raton, FL: CRC Press, LLC 1997.
  4. Ellenhorn MJ, et al. Ellenhorn's Medical Toxicology: Diagnoses and Treatment of Human Poisoning. 2nd ed. Baltimore, MD: Williams & Wilkins, 1997.
  5. Brinker F. Herb Contraindications and Drug Interactions. 2nd ed. Sandy, OR: Eclectic Medical Publications, 1998.
  6. Gossel TA, Bricker JD. Principles of Clinical Toxicology. New York, NY:Raven Press, 1994.
  7. De Smet PAGM, Keller K, Hansel R, Chandler RF, Eds. Adverse Effects of Herbal Drugs 1. Verlag, Berlin: Springer, 1992. DOI
  8. Burnham TH, ed. Drug Facts and Comparisons, Updated Monthly. Facts and Comparisons, St. Louis, MO.
  9. Ramlakhan, S. L. and Fletcher, A. K. It could have happened to Van Gogh: a case of fatal purple foxglove poisoning and review of the literature. Eur.J Emerg.Med 2007;14(6):356-359. PubMed
  10. Yaginuma, M., Orimo, S., Kurosawa, T., Arai, M., and Hiyamuta, E. [Muscle weakness of the upper arms in the last trimester of administering digitalis]. Rinsho Shinkeigaku 1988;28(3):338-341.
  11. Friedman, P. L. and Smith, T. W. Foxglove and Fab: immunological approaches to digitalis intoxication. Int.J.Cardiol. 1983;3(2):237-240. PubMed
  12. Rich, S. A., Libera, J. M., and Locke, R. J. Treatment of foxglove extract poisoning with digoxin-specific Fab fragments. Ann.Emerg.Med 1993;22(12):1904-1907. PubMed
  13. Janssen RM, Berg M, Ovakim DH. Two cases of cardiac glycoside poisoning from accidental foxglove ingestion. CMAJ. 2016;188(10):747-50. PubMed
  14. Lin CC, Yang CC, Phua DH, Deng JF, Lu LH. An outbreak of foxglove leaf poisoning. J Chin Med Assoc. 2010;73(2):97-100. PubMed
  15. Wu IL, Yu JH, Lin CC, Seak CJ, Olson KR, Chen HY. Fatal cardiac glycoside poisoning due to mistaking foxglove for comfrey. Clin Toxicol (Phila). 2017:1-4. PubMed

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 Foxglove and Letrozole Together: Common Questions

Is it safe to take Foxglove with Letrozole?
We do not list a known interaction between Foxglove and Letrozole. 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 Foxglove and Letrozole have any of the same side effects?
Yes — our sources link each of them separately to 3 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.
How was the Foxglove and Letrozole combination checked?
Interactions in our licensed database are recorded against drug classes. Letrozole is filed under 4 classifications, and Foxglove has documented interactions with 6 drug classes — none of Letrozole'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 Foxglove interact with any other medications?
Yes. Foxglove has 133 documented drug interactions in our database — Letrozole 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 Letrozole interact with any supplements?
Yes. Letrozole has documented interactions with 142 supplements in our database — Foxglove is not one of them. The Letrozole 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

Foxglove monograph Uses, safety profile, and every drug interaction in one place Letrozole drug information The full plain-English guide to this medication Letrozole supplement interactions Every supplement checked against Letrozole, 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 19 citations behind this page Ask a pharmacist Free, personal answer from our licensed team

Still Have a Question About Letrozole and Foxglove?

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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.