Drug & supplement interaction

Oregano + 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 Oregano 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

Oregano 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 Oregano 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.

Oregano safety at a glance

Oregano overall Use caution Safe as a food, but concentrated oregano oil supplements are stronger and less studied.
Pregnancy Possibly Unsafe When used orally in medicinal amounts. Oregano is thought to have abortifacient and emmenagogue effects. Read the full pregnancy detail
Breastfeeding Use caution Stick to normal food amounts; safety of supplements while breastfeeding is not established.

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.

Pharmacist analysis

Oregano (and oregano oil) supplements are generally considered safe and there is no indication that there is an interaction between the drug highlighted in this interaction monograph and oregano.

However, as with all supplements, it is important to talk to your doctor before starting anything new, so you can be appropriately monitored.

In terms of drug interactions that have been reported with oregano, below are some examples.

Anticoagulant; Antiplatelet Drugs

Anticoagulants and antiplatelet drugs work by slowing down or preventing blood clotting. While they are essential medications for individuals with certain conditions, they come with an increased risk of bleeding.

Some studies have reported that oregano oil may also increase the risk of bleeding, as it contains compounds that have antithrombin activity and can inhibit platelet aggregation.

Therefore, taking oregano oil along with anticoagulants or antiplatelet drugs may increase the risk of bleeding, bruising, and other adverse effects.

Anti-Diabetic Drugs

Several studies suggest that oregano supplements may help lower blood glucose (i.e., sugar) levels. In vitro and animal research has shown that oregano extracts might stimulate glucose uptake and reduce blood glucose levels.

Therefore, based on the available evidence, combining oregano oil with antidiabetic drugs could potentially cause blood sugar levels to drop too low, leading to hypoglycemia.

However, it is important to note that studies reporting that oregano can reduce blood glucose levels have not reported it causing hypoglycemia.

References

  • Anti-hyperglycaemic activity of the aqueous extract of Origanum vulgare growing wild in Tafilalet region. PubMed
  • Inhibitory effect of clonal oregano extracts against porcine pancreatic amylase in vitro. PubMed
  • Antithrombin activity of some constituents from Origanum vulgare. PubMed
  • Comparative screening of plant essential oils: phenylpropanoid moiety as basic core for antiplatelet activity. PubMed

—

Still wondering about combining Letrozole and Oregano? 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. Oregano has documented interactions with 2 drug classes — the most serious being anticoagulant/antiplatelet drugs (moderate) and 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

Oregano Does Interact With Other Medications

Oregano has 208 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 208 No known interaction 2,622 (incl. Letrozole)
Taking anything else?

Check Another of Your Medications Against Oregano

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

What to actually watch for

No Interaction Found — But Data Suggests Oregano and Letrozole May Share a Side Effect

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

    Oregano

    “Systemic allergic reactions have been reported with oregano. A 45-year-old male developed pruritus, respiratory difficulty, hypotension, swelling of the lips and tongue, and facial edema after ingesting pizza seasoned with oregano. He had 2 similar episodes after ingesting foods seasoned with thyme, another member of the Lamiaceae family.”

    Oregano · Natural Medicines adverse-effect record, reported in hypotension.

    1 source cited
    1. 3705. Benito M, Jorro G, Morales C, et al. Labiatae allergy: systemic reactions due to ingestion of oregano and thyme. Ann Allergy Asthma Immunol 1996;76:416-8. PubMed

    Letrozole

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

Reported for Oregano but not commonly for Letrozole: stomach upset, an allergic reaction, low blood pressure and a severe allergic reaction.

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

Oregano in Pregnancy & Breastfeeding

Pregnancy Possibly Unsafe

When used orally in medicinal amounts. Oregano is thought to have abortifacient and emmenagogue effects.

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

We hold 1,632 real supplement products containing Oregano, each one broken down to its full ingredient list — and combination products often carry several ingredients besides Oregano. Even though Oregano 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 Oregano 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 Oregano
Top 10%

#133 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 Oregano reference on this page ↓
  • Freshness: we automatically re-check this combination every week — this pair was last verified September 13, 2026. The Oregano and Letrozole records this page draws on were last updated July 11, 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 Oregano

What is Oregano?

Oregano
  • Digestive upset
  • Respiratory and cold symptoms
  • Antimicrobial support
  • Intestinal parasites
  • Skin and fungal concerns

Oregano is a common Mediterranean cooking herb that is also sold as a concentrated oil or supplement, often standardized for a compound called carvacrol. While lab studies suggest it may have antimicrobial and antioxidant properties, strong human evidence for treating any specific health condition is limited. Used as a food, oregano is very safe; concentrated oregano oil supplements should be used cautiously and discussed with your pharmacist or doctor.

Origanum vulgare · Lamiaceae · Leaves and essential oil · Culinary herb, tea, capsules, softgels, liquid oil (oil of oregano), tinctures

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

Oregano: dosing

There is no official, well-established dose for oregano supplements. Products vary widely in strength and in how much carvacrol they contain, so it is hard to compare them.The safest approach is to follow the directions on the product label and not exceed the recommended amount.

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

Read the full Oregano 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 & Oregano

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

0Major
208Moderate
0Minor
2,621No known interaction
208 Moderate 2,621 No interaction
Moderate

208 interactions

Showing 60 of 208 moderate interactions — see all 208 on the Oregano page.

No interaction 2,621 drugs checked — show the list

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

Showing the 60 most looked-up of 2,621 medications checked with no known interaction — see the full Oregano list.

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

Oregano References

The 12 references that drive our Oregano 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. Brinker F. Herb Contraindications and Drug Interactions. 2nd ed. Sandy, OR: Eclectic Medical Publications, 1998.
  2. Benito M, Jorro G, Morales C, et al. Labiatae allergy: systemic reactions due to ingestion of oregano and thyme. Ann Allergy Asthma Immunol 1996;76:416-8. PubMed
  3. Chevallier A. Encyclopedia of Herbal Medicine. 2nd ed. New York, NY: DK Publ, Inc., 2000.
  4. Ciganda C, and Laborde A. Herbal infusions used for induced abortion. J Toxicol.Clin Toxicol. 2003;41:235-239. PubMed
  5. Futrell, J. M. and Rietschel, R. L. Spice allergy evaluated by results of patch tests. Cutis 1993;52(5):288-290.
  6. Tognolini, M., Barocelli, E., Ballabeni, V., Bruni, R., Bianchi, A., Chiavarini, M., and Impicciatore, M. Comparative screening of plant essential oils: phenylpropanoid moiety as basic core for antiplatelet activity. Life Sci. 2-23-2006;78(13):1419-1432. PubMed
  7. Goun, E., Cunningham, G., Solodnikov, S., Krasnykch, O., and Miles, H. Antithrombin activity of some constituents from Origanum vulgare. Fitoterapia 2002;73(7-8):692-694. PubMed
  8. Lemhadri, A., Zeggwagh, N. A., Maghrani, M., Jouad, H., and Eddouks, M. Anti-hyperglycaemic activity of the aqueous extract of Origanum vulgare growing wild in Tafilalet region. J Ethnopharmacol. 2004;92(2-3):251-256. PubMed
  9. McCue, P., Vattem, D., and Shetty, K. Inhibitory effect of clonal oregano extracts against porcine pancreatic amylase in vitro. Asia Pac.J Clin.Nutr. 2004;13(4):401-408.
  10. Ragi, J., Pappert, A., Rao, B., Havkin-Frenkel, D., and Milgraum, S. Oregano extract ointment for wound healing: a randomized, double-blind, petrolatum-controlled study evaluating efficacy. J.Drugs Dermatol. 2011;10(10):1168-1172.
  11. Singletary K. Oregano: overview of the literature on health benefits. Nutrition Today 2010;45(3):129-38.
  12. Silva MLAE, Lucarini R, Dos Santos FF, et al. Hypoglycemic effect of rosmarinic acid-rich infusion (RosCE) from Origanum vulgare in alloxan-induced diabetic rats. Nat Prod Res 2022;36(17):4525-4531.

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 Oregano and Letrozole Together: Common Questions

Is it safe to take Oregano with Letrozole?
We do not list a known interaction between Oregano 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 Oregano and Letrozole have any of the same side effects?
Yes — our sources link each of them separately to one 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 Oregano and Letrozole combination checked?
Interactions in our licensed database are recorded against drug classes. Letrozole is filed under 4 classifications, and Oregano has documented interactions with 2 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 Oregano interact with any other medications?
Yes. Oregano has 208 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 — Oregano 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

Oregano 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 12 citations behind this page Ask a pharmacist Free, personal answer from our licensed team

Still Have a Question About Letrozole and Oregano?

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.