Drug & supplement interaction

Brewer's Yeast + 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 Brewer's Yeast 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

Brewer's Yeast 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 Brewer's Yeast 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.

Brewer's Yeast safety at a glance

Brewer's Yeast overall Use caution Generally well tolerated in food amounts, but it can cause gas and may not be safe for people with weakened immune systems or certain conditions.
Pregnancy Use caution Likely fine in normal food amounts, but the safety of concentrated supplements during pregnancy is not well studied, so check with your provider.
Breastfeeding Use caution Food amounts are likely fine, but there is not enough information on supplement doses, so use caution and ask your provider.

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

Still wondering about combining Letrozole and Brewer's Yeast? 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. Brewer's Yeast has documented interactions with 4 drug classes — the most serious being monoamine oxidase inhibitors (maois) (major), antidiabetes drugs (moderate) and lithium (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

Brewer's Yeast Does Interact With Other Medications

Brewer's Yeast has 9 major, 87 moderate, 40 minor 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 9 Moderate 87 Minor 40 No known interaction 2,694 (incl. Letrozole)
Taking anything else?

Check Another of Your Medications Against Brewer's Yeast

Covers the 2,830 medications we’ve checked against Brewer's Yeast. Pick one to open its full report.

What to actually watch for

No Interaction Found — But Data Suggests Brewer's Yeast 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

    Brewer's Yeast

    “Allergic reactions to brewer's yeast can occur in hypersensitive individuals. Symptoms include itching, urticaria, local or general exanthemas, and Quincke's edema (2). Rarely, anaphylaxis may occur. In one case, a 33-year-old male experienced dyspnea, chest tightness, and throat tightness shortly after ingesting a few sips of craft beer brewed using brewer's yeast.”

    Brewer's Yeast · Natural Medicines adverse-effect record, reported in pruritus.

    2 sources cited
    1. 2. Blumenthal M, ed. The Complete German Commission E Monographs: Therapeutic Guide to Herbal Medicines. Trans. S. Klein. Boston, MA: American Botanical Council, 1998.
    2. 111107. Mourey F, Decherf A, Jeanne JF, et al. Saccharomyces cerevisiae I-3856 in irritable bowel syndrome with predominant constipation. World J Gastroenterol 2022;28(22):2509-2522.

    Letrozole

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

  • Headache Additional detail

    Brewer's Yeast

    “Orally, brewer's yeast can cause migraine-like headaches in sensitive individuals (2).”

    Brewer's Yeast · Natural Medicines adverse-effect record, reported in migraine headache.

    1 source cited
    1. 2. Blumenthal M, ed. The Complete German Commission E Monographs: Therapeutic Guide to Herbal Medicines. Trans. S. Klein. Boston, MA: American Botanical Council, 1998.

    Letrozole

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

Reported for Brewer's Yeast but not commonly for Letrozole: an allergic reaction, chest pain, stomach pain and a severe allergic reaction.

Effects for Letrozole come from the ADVERSE REACTIONS section of its FDA label; effects for Brewer's Yeast 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.

From our Q&A

Questions About Brewer's Yeast 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 Brewer's Yeast 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 Brewer's Yeast 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 Brewer's Yeast as Part of a Dietary Supplement Product? Check It for Interactions

We hold 126 real supplement products containing Brewer's Yeast, each one broken down to its full ingredient list — and combination products often carry several ingredients besides Brewer's Yeast. Even though Brewer's Yeast 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 Brewer's Yeast 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 Brewer's Yeast
Top half

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

What is Brewer's Yeast?

Brewer's Yeast
  • Source of B vitamins
  • Diarrhea (certain types)
  • Cold and flu support
  • Digestive health
  • Acne and skin health
  • Blood sugar support

Brewer's yeast is a nutrient-rich fungus that provides B vitamins, protein, and minerals, and a related yeast product (S. boulardii) is used for some types of diarrhea. Most other health claims have limited or weak evidence. It is generally well tolerated as a food or supplement, but talk to your pharmacist or doctor before using it regularly, especially if you have a weakened immune system.

Saccharomyces cerevisiae · Saccharomycetaceae · Whole dried yeast cells (and their fermentation products) · Tablets, capsules, powder, flakes, liquid

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

Brewer's Yeast: dosing

There is no single official or proven dose for brewer's yeast. Products vary widely in their form (tablets, powder, flakes) and in how much yeast they contain.The best approach is to follow the directions on the product label and start with a lower amount to see how your stomach handles it. They can help you decide whether it is appropriate and whether a different, better-studied product (such as a specific probiotic) might be a better fit.

From our Brewer's Yeast monograph — the full record covers uses, side effects and every documented interaction.

Read the full Brewer's Yeast 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 & Brewer's Yeast

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

9Major
87Moderate
40Minor
2,693No known interaction
9 Major 87 Moderate 40 Minor 2,693 No interaction
Major

9 interactions

Moderate

87 interactions

Showing 60 of 87 moderate interactions — see all 87 on the Brewer's Yeast page.

Minor

40 interactions

No interaction 2,693 drugs checked — show the list

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

Showing the 60 most looked-up of 2,693 medications checked with no known interaction — see the full Brewer's Yeast list.

See the full Brewer's Yeast interactions page
See every supplement checked against Letrozole, ranked by severity
Evidence & sources

Brewer's Yeast References

The 6 references that drive our Brewer's Yeast 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. Lewis SJ, Freedman AR. Review article: the use of biotherapeutic agents in the prevention and treatment of gastrointestinal disease. Aliment Pharmacol Ther 1998;12:807-22. PubMed
  3. Bahijiri, S. M., Mira, S. A., Mufti, A. M., and Ajabnoor, M. A. The effects of inorganic chromium and brewer's yeast supplementation on glucose tolerance, serum lipids and drug dosage in individuals with type 2 diabetes. Saudi.Med.J. 2000;21(9):831-837. DOI
  4. Schrauzer, G. N. and de, Vroey E. Effects of nutritional lithium supplementation on mood. A placebo-controlled study with former drug users. Biol.Trace Elem.Res. 1994;40(1):89-101. PubMed
  5. Gayathri R, Aruna T, Malar S, Shilpa B, Dhanasekar KR. Efficacy of Saccharomyces cerevisiae CNCM I-3856 as an add-on therapy for irritable bowel syndrome. Int J Colorectal Dis. 2020;35(1):139-145. PubMed
  6. Mourey F, Decherf A, Jeanne JF, et al. Saccharomyces cerevisiae I-3856 in irritable bowel syndrome with predominant constipation. World J Gastroenterol 2022;28(22):2509-2522.

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 Brewer's Yeast and Letrozole Together: Common Questions

Is it safe to take Brewer's Yeast with Letrozole?
We do not list a known interaction between Brewer's Yeast 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 Brewer's Yeast and Letrozole have any of the same side effects?
Yes — our sources link each of them separately to 2 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 Brewer's Yeast and Letrozole combination checked?
Interactions in our licensed database are recorded against drug classes. Letrozole is filed under 4 classifications, and Brewer's Yeast has documented interactions with 4 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 Brewer's Yeast interact with any other medications?
Yes. Brewer's Yeast has 136 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 — Brewer's Yeast 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

Brewer's Yeast 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 6 citations behind this page Ask a pharmacist Free, personal answer from our licensed team

Still Have a Question About Letrozole and Brewer's Yeast?

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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.