Drug & supplement interaction

Arsenic + 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 Arsenic 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

Arsenic 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 Arsenic 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.

Arsenic safety at a glance

Arsenic overall Avoid Inorganic arsenic is a known poison and carcinogen and should not be taken as a supplement.
Pregnancy Likely Safe When organic arsenic is consumed in food amounts. Organic forms of arsenic found in a normal diet have not been linked to toxicity. Read the full pregnancy detail
Breastfeeding Likely Safe When organic arsenic is consumed in food amounts. Organic forms of arsenic found in a normal diet have not been linked to toxicity. 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 Arsenic? 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. Arsenic has documented interactions with 1 drug class — the most serious being qt interval-prolonging drugs (major) — 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

Arsenic Does Interact With Other Medications

Arsenic has 161 major, 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 161 No known interaction 2,669 (incl. Letrozole)
Taking anything else?

Check Another of Your Medications Against Arsenic

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

What to actually watch for

No Interaction Found — But Data Suggests Arsenic 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. One of them is worth acting on rather than waiting out — marked below.

  • Bleeding or bruising Worth acting on Additional detail

    Arsenic

    “Orally, organic forms of arsenic found in the diet are well tolerated, with no clear links to adverse effects. However, high doses or chronic intake of inorganic arsenic is associated with potentially serious adverse effects.

    Serious Adverse Effects (Rare):

    Orally: With the acute ingestion of inorganic arsenic, anemia, arrhythmias, bruising, gastrointestinal irritation or damage, hepatotoxicity, and peripheral neurop…”

    Arsenic · Natural Medicines adverse-effect record, reported in anemia.

    “Orally, doses of inorganic arsenic 1 mg/kg daily can cause hematopoietic depression including anemia, arrhythmias, and blood vessel damage leading to bruising. Acute ingestion of inorganic arsenic 10 mg/kg daily or more causes vasodilation and myocardial depression leading to myocardial injury, shock, and circulatory failure (17,7135,16313,16316,102892).”

    Arsenic · Natural Medicines adverse-effect record, reported in anemia.

    6 sources cited
    1. 7135. Food and Nutrition Board, Institute of Medicine. Dietary Reference Intakes for Vitamin A, Vitamin K, Arsenic, Boron, Chromium, Copper, Iodine, Iron, Manganese, Molybdenum, Nickel, Silicon, Vanadium, and Zinc. Washington, DC: National Academy Press, 2002.
    2. 16309. Uthus EO, Seaborn CD. Deliberations and evaluations of the approaches, endpoints and paradigms for dietary recommendations of the other trace elements. J Nutr 1996;126:2452s-2459s. PubMed
    3. 16312. US Department of Health and Human Services. Agency for Toxic Substances and Disease Registry. Public Health Statement: Arsenic. August 2007. Available at: www.atsdr.cdc.gov/toxprofiles/tp2-c1-b.pdf (Accessed 14 April 2008).
    4. 17. Ellenhorn MJ, et al. Ellenhorn's Medical Toxicology: Diagnoses and Treatment of Human Poisoning. 2nd ed. Baltimore, MD: Williams & Wilkins, 1997.
    5. 16313. Eckhert CD. Other trace elements. In: Shils ME, Shike M, Ross AC, et al (eds). Modern Nutrition in Health and Disease. 10th ed. Philadelphia, PA: Lippincott Williams & Wilkins, 2006.
    6. 16316. Ratnaike RN. Acute and chronic arsenic toxicity. Postgrad Med J 2003;79:391-6. PubMed

    Letrozole

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

  • Swelling / Dizziness / Headache Additional detail

    Arsenic

    “Orally, doses of inorganic arsenic 1 mg/kg daily can cause peripheral neuropathy and encephalopathy. In one case, chronic intake of inorganic arsenic 30 ng daily has reportedly caused headache, dizziness, and difficulty concentrating. Acute ingestion of inorganic arsenic 10 mg/kg daily or more can cause cerebral edema, leading to encephalopathy, convulsions, coma, and death (17,7135,16313,16316).”

    Arsenic · Natural Medicines adverse-effect record, reported in cluster headache.

    6 sources cited
    1. 7135. Food and Nutrition Board, Institute of Medicine. Dietary Reference Intakes for Vitamin A, Vitamin K, Arsenic, Boron, Chromium, Copper, Iodine, Iron, Manganese, Molybdenum, Nickel, Silicon, Vanadium, and Zinc. Washington, DC: National Academy Press, 2002.
    2. 16309. Uthus EO, Seaborn CD. Deliberations and evaluations of the approaches, endpoints and paradigms for dietary recommendations of the other trace elements. J Nutr 1996;126:2452s-2459s. PubMed
    3. 16312. US Department of Health and Human Services. Agency for Toxic Substances and Disease Registry. Public Health Statement: Arsenic. August 2007. Available at: www.atsdr.cdc.gov/toxprofiles/tp2-c1-b.pdf (Accessed 14 April 2008).
    4. 102893. Dani SU. A curious association of chronic homeopathic arsenic ingestion with nonspecific symptoms in a Swiss teenager. Swiss Med Wkly 2019;149:w20071. PubMed
    5. 17. Ellenhorn MJ, et al. Ellenhorn's Medical Toxicology: Diagnoses and Treatment of Human Poisoning. 2nd ed. Baltimore, MD: Williams & Wilkins, 1997.
    6. 16313. Eckhert CD. Other trace elements. In: Shils ME, Shike M, Ross AC, et al (eds). Modern Nutrition in Health and Disease. 10th ed. Philadelphia, PA: Lippincott Williams & Wilkins, 2006.

    Letrozole

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

Reported for Arsenic but not commonly for Letrozole: stomach upset, trouble concentrating, numbness or tingling and kidney problems.

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

Arsenic in Pregnancy & Breastfeeding

Pregnancy And Lactation Likely Safe

When organic arsenic is consumed in food amounts. Organic forms of arsenic found in a normal diet have not been linked to toxicity.

Pregnancy And Lactation Likely Unsafe

When inorganic arsenic is taken orally, especially when used long-term or in high doses. While exposure to inorganic arsenic in drinking water does not seem to increase the risk of neural tube defects, it has been associated with an increased risk for spontaneous abortion, stillbirth, and neonatal mortality. Exposure to inorganic arsenic in drinking water and other sources while pregnant has also been linked to changes in birth weight, length, and head circumference, with one study showing that higher maternal blood arsenic levels are associated with 44% greater odds of delivering a small for gestational age infant and 103% greater odds of delivering a large for gestational age infant. Avoid arsenic supplements and water contaminated with arsenic during pregnancy or lactation.

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

We hold 4 real supplement products containing Arsenic, each one broken down to its full ingredient list — and combination products often carry several ingredients besides Arsenic. Even though Arsenic 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 Arsenic 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 Arsenic
Steady interest

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

What is Arsenic?

Arsenic
  • Homeopathic digestive complaints
  • Traditional remedy for inflammatory conditions
  • Prescription use in certain leukemias (medical, not supplement)
  • Anxiety and restlessness (homeopathic tradition)

Arsenic is a naturally occurring element that is toxic in its inorganic form, and it is not a supplement you should take to improve your health. While arsenic trioxide is a real, doctor-prescribed cancer medicine, and tiny homeopathic doses exist, there is no good reason to take arsenic on your own. Avoid arsenic-containing products and talk to a pharmacist or doctor about any concerns.

Mineral/trace element (not a plant part) · Homeopathic preparations (e.g. Arsenicum album), trace amounts in food and water

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

Arsenic: dosing

There is no safe or recommended supplement dose of arsenic. It is not a nutrient you need to add to your diet, and no health authority recommends taking arsenic supplements.Homeopathic products that list arsenic are usually extremely dilute, but they still have no proven benefit. The only legitimate dosed use of arsenic is the prescription medicine arsenic trioxide, which is calculated and given by cancer specialists in a hospital setting.If you are considering any product that contains arsenic, do not guess at a dose.

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

Read the full Arsenic 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 & Arsenic

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

161Major
0Moderate
0Minor
2,668No known interaction
161 Major 2,668 No interaction
Major

161 interactions

Showing 60 of 161 major interactions — see all 161 on the Arsenic page.

No interaction 2,668 drugs checked — show the list

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

Showing the 60 most looked-up of 2,668 medications checked with no known interaction — see the full Arsenic list.

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

Arsenic References

The 35 references that drive our Arsenic 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. McEvoy GK, ed. AHFS Drug Information. Bethesda, MD: American Society of Health-System Pharmacists, 1998.
  2. Ellenhorn MJ, et al. Ellenhorn's Medical Toxicology: Diagnoses and Treatment of Human Poisoning. 2nd ed. Baltimore, MD: Williams & Wilkins, 1997.
  3. Food and Nutrition Board, Institute of Medicine. Dietary Reference Intakes for Vitamin A, Vitamin K, Arsenic, Boron, Chromium, Copper, Iodine, Iron, Manganese, Molybdenum, Nickel, Silicon, Vanadium, and Zinc. Washington, DC: National Academy Press, 2002.
  4. Uthus EO, Seaborn CD. Deliberations and evaluations of the approaches, endpoints and paradigms for dietary recommendations of the other trace elements. J Nutr 1996;126:2452s-2459s. PubMed
  5. Nielsen FH. Nutritional requirements for boron, silicon, vanadium, nickel, and arsenic: current knowledge and speculation. FASEB J 1991;5:2661-7. DOI
  6. US Department of Health and Human Services. Agency for Toxic Substances and Disease Registry. Public Health Statement: Arsenic. August 2007. Available at: www.atsdr.cdc.gov/toxprofiles/tp2-c1-b.pdf (Accessed 14 April 2008).
  7. Eckhert CD. Other trace elements. In: Shils ME, Shike M, Ross AC, et al (eds). Modern Nutrition in Health and Disease. 10th ed. Philadelphia, PA: Lippincott Williams & Wilkins, 2006.
  8. Ratnaike RN. Acute and chronic arsenic toxicity. Postgrad Med J 2003;79:391-6. PubMed
  9. Wasserman GA, Liu X, Parvez F, et al. Water arsenic exposure and children's intellectual function in Araihazar, Bangladesh. Environ Health Perspect 2004;112:1329-33. PubMed
  10. Lamm SH, Ferdosi H, Dissen EK, Li J, Ahn J. A systematic review and meta-regression analysis of lung cancer risk and inorganic arsenic in drinking water. Int J Environ Res Public Health 2015;12(12):15498-515. PubMed
  11. Hsueh YM, Chen WJ, Lee CY, et al. Association of arsenic methylation capacity with developmental delays and health status in children: a prospective case-control trial. Sci Rep 2016;6:37287. PubMed
  12. Moon KA, Oberoi S, Barchowsky A, et al. A dose-response meta-analysis of chronic arsenic exposure and incident cardiovascular disease. Int J Epidemiol 2017;46(6):1924-39. PubMed
  13. Dong J, Su SY. The association between arsenic and children's intelligence: a meta-analysis. Biol Trace Elem Res 2009;129(1-3):88-93. PubMed
  14. Nong Q, Zhang Y, Guallar E, Zhong Q. Arsenic exposure and predicted 10-year atherosclerotic cardiovascular risk using the pooled cohort equations in U.S. hypertensive adults. Int J Environ Res Public Health 2016;13(11). pii: E1093. PubMed
  15. Sung TC, Huang JW, Guo HR. Association between arsenic exposure and diabetes: a meta-analysis. Biomed Res Int 2015;2015:368087. 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 Arsenic and Letrozole Together: Common Questions

Is it safe to take Arsenic with Letrozole?
We do not list a known interaction between Arsenic 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 Arsenic and Letrozole have any of the same side effects?
Yes — our sources link each of them separately to 4 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 Arsenic and Letrozole combination checked?
Interactions in our licensed database are recorded against drug classes. Letrozole is filed under 4 classifications, and Arsenic has documented interactions with 1 drug class — 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 Arsenic interact with any other medications?
Yes. Arsenic has 161 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 — Arsenic 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

Arsenic 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 35 citations behind this page Ask a pharmacist Free, personal answer from our licensed team

Still Have a Question About Letrozole and Arsenic?

Our pharmacists answer your medication & supplement questions — free.

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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.