Drug & supplement interaction

Eyebright + 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 Eyebright 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

Eyebright 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 Eyebright 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.

Eyebright safety at a glance

Eyebright overall Use caution Likely safe in small amounts as a tea, but using homemade or non-sterile preparations directly in the eye is risky.
Pregnancy Avoid Safety has not been established, so it is best avoided during pregnancy.
Breastfeeding Avoid There is not enough safety information, so avoid use while breastfeeding.

Safety guidance is general; always confirm with your pharmacist or doctor for your situation.

Still wondering about combining Letrozole and Eyebright? 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. Eyebright has documented interactions with 1 drug class — the most serious being antidiabetes 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

Eyebright Does Interact With Other Medications

Eyebright has 86 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.

Moderate 86 No known interaction 2,744 (incl. Letrozole)
Taking anything else?

Check Another of Your Medications Against Eyebright

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

What to actually watch for

No Interaction Found — But Data Suggests Eyebright 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.

  • Swelling Additional detail

    Eyebright

    “Topically, eyebright has been reported to cause increased ocular pressure, lacrimation, pruritus, redness, swelling of eyelid margins, vision changes, and photophobia when applied to the eyes (4). Ophthalmic eyebright products should be used with caution due to the potential for contamination (8,11).”

    Eyebright · Natural Medicines adverse-effect record, reported in pruritus.

    3 sources cited
    1. 4. Newall CA, Anderson LA, Philpson JD. Herbal Medicine: A Guide for Healthcare Professionals. London, UK: The Pharmaceutical Press, 1996.
    2. 8. Wichtl MW. Herbal Drugs and Phytopharmaceuticals. Ed. N.M. Bisset. Stuttgart: Medpharm GmbH Scientific Publishers, 1994.
    3. 11. Leung AY, Foster S. Encyclopedia of Common Natural Ingredients Used in Food, Drugs and Cosmetics. 2nd ed. New York, NY: John Wiley & Sons, 1996.

    Letrozole

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

  • Headache Additional detail

    Eyebright

    “Orally, eyebright has been reported to cause confusion and headache (4).”

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

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

    Letrozole

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

  • Nausea Additional detail

    Eyebright

    “Orally, eyebright has been reported to cause nausea and constipation (4).”

    Eyebright · Natural Medicines adverse-effect record, reported in constipation.

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

    Letrozole

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

Reported for Eyebright but not commonly for Letrozole: a stuffy or runny nose, blurred vision, constipation and confusion.

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

Overlapping uses

What Letrozole Is Prescribed For, and What Eyebright Has Been Studied For

These two come up together because they touch the same health topic — not because they do the same job. Letrozole is a prescription medicine with approved uses on its FDA label. Eyebright is a supplement: what follows is what researchers have looked at it for, and how strong that evidence is.

Letrozole is prescribed for: 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.

Eyebright has been studied for:

  • Cancer studied, not established Eyebright has been studied for this. Natural Medicines rates the evidence: Insufficient Reliable Evidence To Rate Read what the research shows

    Eyebright for cancer

    Although there has been interest in using oral eyebright for cancer, there is insufficient reliable information about the clinical effects of eyebright for this purpose.

Effectiveness ratings and the research summaries above are the verbatim record from the Natural Medicines database, which grades evidence from “Effective” down to “Insufficient Reliable Evidence To Rate”. A rating below the top of that scale means researchers have looked at it — not that it works, and never that it can stand in for a prescribed medicine. Do not stop or replace Letrozole on your own; if you are taking Eyebright for the same health topic, tell your prescriber, especially if the medicine is being adjusted to a target.

From our Q&A

Questions About Eyebright 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 Eyebright 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 Eyebright 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 Eyebright as Part of a Dietary Supplement Product? Check It for Interactions

We hold 504 real supplement products containing Eyebright, each one broken down to its full ingredient list — and combination products often carry several ingredients besides Eyebright. Even though Eyebright 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 Eyebright 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 Eyebright
Top half

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

What is Eyebright?

Eyebright
  • Eye irritation and redness
  • Conjunctivitis (pink eye)
  • Eye strain
  • Allergy and cold-related eye symptoms
  • Nasal congestion and hay fever

Eyebright is a traditional herb long used for minor eye irritation, redness, and allergy symptoms, but high-quality human studies are very limited. There is not enough reliable evidence to confirm it works, and using non-sterile herbal preparations in the eye carries a real risk of infection, so talk to your pharmacist or doctor before trying it.

Euphrasia officinalis · Orobanchaceae · Aerial parts (leaves, stems, and flowers) · Tea, eye drops, tincture, capsules, homeopathic preparations, compresses

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

Eyebright: dosing

There is no standardized or well-established dose for eyebright. Traditional use as a tea typically involves steeping the dried herb in hot water, but amounts vary widely between products and sources.If you choose to use a commercial eyebright product, follow the directions on the label and choose products from reputable manufacturers. For anything used in or near the eye, only use products that are specifically made and labeled as sterile eye preparations.

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

Read the full Eyebright 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 & Eyebright

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

0Major
86Moderate
0Minor
2,743No known interaction
86 Moderate 2,743 No interaction
Moderate

86 interactions

Showing 60 of 86 moderate interactions — see all 86 on the Eyebright page.

No interaction 2,743 drugs checked — show the list

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

Showing the 60 most looked-up of 2,743 medications checked with no known interaction — see the full Eyebright list.

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

Eyebright References

The 4 references that drive our Eyebright 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. Newall CA, Anderson LA, Philpson JD. Herbal Medicine: A Guide for Healthcare Professionals. London, UK: The Pharmaceutical Press, 1996.
  2. Wichtl MW. Herbal Drugs and Phytopharmaceuticals. Ed. N.M. Bisset. Stuttgart: Medpharm GmbH Scientific Publishers, 1994.
  3. Leung AY, Foster S. Encyclopedia of Common Natural Ingredients Used in Food, Drugs and Cosmetics. 2nd ed. New York, NY: John Wiley & Sons, 1996.
  4. Porchezhian, E., Ansari, S. H., and Shreedharan, N. K. Antihyperglycemic activity of Euphrasia officinale leaves. Fitoterapia 2000;71(5):522-526. 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 Eyebright and Letrozole Together: Common Questions

Is it safe to take Eyebright with Letrozole?
We do not list a known interaction between Eyebright 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 Eyebright 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.
Are Eyebright and Letrozole used for the same thing?
They overlap in purpose, which usually means the real question is whether you need both rather than whether they are safe together. This page lists the shared uses and how strong the evidence is for Eyebright in each. That is a conversation for your prescriber, especially if Letrozole is being adjusted to a target.
How was the Eyebright and Letrozole combination checked?
Interactions in our licensed database are recorded against drug classes. Letrozole is filed under 4 classifications, and Eyebright 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 Eyebright interact with any other medications?
Yes. Eyebright has 86 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 — Eyebright 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

Eyebright 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 4 citations behind this page Ask a pharmacist Free, personal answer from our licensed team

Still Have a Question About Letrozole and Eyebright?

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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.