Drug & supplement interaction

Parsley + 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 Parsley 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

Parsley 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 Parsley 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.

Parsley safety at a glance

Parsley overall Use caution Safe as a food, but concentrated extracts, seeds, and essential oil may not be safe in large amounts.
Pregnancy Likely Unsafe When used orally in medicinal amounts. Parsley has been used orally as an abortifacient and to stimulate menstrual flow. Population evidence suggests that mater... Read the full pregnancy detail
Breastfeeding Use caution Food amounts are likely fine, but avoid concentrated supplements due to lack of safety data.

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 Parsley? 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. Parsley has documented interactions with 8 drug classes — the most serious being anticoagulant/antiplatelet drugs (moderate), antidiabetes drugs (moderate) and cytochrome p450 1a2 (cyp1a2) substrates (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

Parsley Does Interact With Other Medications

Parsley has 443 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 443 No known interaction 2,387 (incl. Letrozole)
Taking anything else?

Check Another of Your Medications Against Parsley

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

What to actually watch for

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

  • Bleeding or bruising Worth acting on Additional detail

    Parsley

    “Orally, parsley seems to be well tolerated when used low to moderate doses. Large doses may be unsafe.

    Serious Adverse Effects (Rare):

    Orally, Hallucinations, hemolytic anemia, hypotension, hepatic impairment, kidney impairment, nephrotic syndrome, paralysis, and thrombocytopenia purpura when taken in very high doses (200 grams parsley oil or 10 grams or more of parsley's apiole or myristicin constituents).”

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

    “Parsley contains the potentially toxic constituent apiole, which can cause significant adverse effects at high doses (11). Adverse effects specifically associated with more than 10 grams of the constituent apiole include hemolytic anemia and thrombocytopenia purpura (4).”

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

    2 sources cited
    1. 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.
    2. 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 Parsley but not commonly for Letrozole: a low platelet count, hallucinations, a slow heartbeat and low blood pressure.

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

Parsley in Pregnancy & Breastfeeding

Pregnancy Likely Unsafe

When used orally in medicinal amounts. Parsley has been used orally as an abortifacient and to stimulate menstrual flow. Population evidence suggests that maternal intake of An-Tai-Yin, an herbal combination product containing parsley and dong quai, during the first trimester increases the risk of congenital malformations of the musculoskeletal system, connective tissue, and eyes.

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

We hold 3,292 real supplement products containing Parsley, each one broken down to its full ingredient list — and combination products often carry several ingredients besides Parsley. Even though Parsley 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 Parsley 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 Parsley
Top 10%

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

What is Parsley?

Parsley
  • Water retention and bloating
  • Urinary and bladder support
  • Digestive upset
  • Freshening breath
  • Source of vitamins and antioxidants

Parsley is a popular culinary herb that is safe to eat in normal food amounts and is a good source of vitamins K and C. It is traditionally used as a diuretic and for digestion, but solid human evidence for medicinal benefits is limited. Concentrated supplements, seed extracts, and the essential oil are much stronger than food and should be used cautiously, especially during pregnancy.

Petroselinum crispum · Apiaceae · Leaves, seeds, root, and essential oil · Fresh or dried herb, tea, capsules, extracts, seed oil, essential oil

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

Parsley: dosing

There is no well-established standardized medicinal dose for parsley. Using it as a food or in a cup of parsley tea is the most common and lowest-risk way to take it.If you choose a parsley supplement, follow the directions on the product label and do not exceed the recommended amount. Avoid the concentrated essential oil and high-dose seed products unless guided by a healthcare professional.

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

Read the full Parsley 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 & Parsley

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

0Major
443Moderate
0Minor
2,386No known interaction
443 Moderate 2,386 No interaction
Moderate

443 interactions

Showing 60 of 443 moderate interactions — see all 443 on the Parsley page.

No interaction 2,386 drugs checked — show the list

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

Showing the 60 most looked-up of 2,386 medications checked with no known interaction — see the full Parsley list.

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

Parsley References

The 21 references that drive our Parsley 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. Leung AY, Foster S. Encyclopedia of Common Natural Ingredients Used in Food, Drugs and Cosmetics. 2nd ed. New York, NY: John Wiley & Sons, 1996.
  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. Brinker F. Herb Contraindications and Drug Interactions. 2nd ed. Sandy, OR: Eclectic Medical Publications, 1998.
  5. Robbers JE, Tyler VE. Tyler's Herbs of Choice: The Therapeutic Use of Phytomedicinals. New York, NY: The Haworth Herbal Press, 1999.
  6. Foster S, Tyler VE. Tyler's Honest Herbal, 4th ed., Binghamton, NY: Haworth Herbal Press, 1999. DOI
  7. Eberhard P, Gall HM, Muller I, Moller R. Dramatic augmentation of a food allergy by acetylsalicylic acid. J Allergy Clin Immunol 2000;105:844 PubMed
  8. Tunali T, Yarat A, Yanardag R, et al. Effect of parsley (Petroselinum crispum) on the skin of STZ induced diabetic rats. Phytother Res 1999;13:138-41.. DOI
  9. Chuang CH, Doyle P, Wang JD, et al. Herbal medicines used during the first trimester and major congenital malformations: an analysis of data from a pregnancy cohort study. Drug Saf 2006;29:537-48. PubMed
  10. Ciganda C, and Laborde A. Herbal infusions used for induced abortion. J Toxicol.Clin Toxicol. 2003;41:235-239. PubMed
  11. Jakovljevic, V., Raskovic, A., Popovic, M., and Sabo, J. The effect of celery and parsley juices on pharmacodynamic activity of drugs involving cytochrome P450 in their metabolism. Eur.J Drug Metab Pharmacokinet. 2002;27(3):153-156. PubMed
  12. Kreydiyyeh, S. I. and Usta, J. Diuretic effect and mechanism of action of parsley. J Ethnopharmacol 2002;79(3):353-357. PubMed
  13. Yanardag, R., Bolkent, S., Tabakoglu-Oguz, A., and Ozsoy-Sacan, O. Effects of Petroselinum crispum extract on pancreatic B cells and blood glucose of streptozotocin-induced diabetic rats. Biol Pharm Bull. 2003;26(8):1206-1210. PubMed
  14. Bolkent, S., Yanardag, R., Ozsoy-Sacan, O., and Karabulut-Bulan, O. Effects of parsley (Petroselinum crispum) on the liver of diabetic rats: a morphological and biochemical study. Phytother.Res 2004;18(12):996-999.
  15. Ozsoy-Sacan, O., Yanardag, R., Orak, H., Ozgey, Y., Yarat, A., and Tunali, T. Effects of parsley (Petroselinum crispum) extract versus glibornuride on the liver of streptozotocin-induced diabetic rats. J Ethnopharmacol 3-8-2006;104(1-2):175-181. 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 Parsley and Letrozole Together: Common Questions

Is it safe to take Parsley with Letrozole?
We do not list a known interaction between Parsley 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 Parsley 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 Parsley and Letrozole combination checked?
Interactions in our licensed database are recorded against drug classes. Letrozole is filed under 4 classifications, and Parsley has documented interactions with 8 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 Parsley interact with any other medications?
Yes. Parsley has 443 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 — Parsley 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

Parsley 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 21 citations behind this page Ask a pharmacist Free, personal answer from our licensed team

Still Have a Question About Letrozole and Parsley?

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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.