Drug & supplement interaction

Gravel Root + 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 Gravel Root 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.

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Interaction report

Gravel Root 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 Gravel Root 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.

Gravel Root safety at a glance

Gravel Root overall Use caution Limited safety data and possible liver-toxic compounds mean it should be used cautiously and short-term.
Pregnancy Likely Unsafe When used orally. Gravel root preparations containing hepatotoxic pyrrolizidine alkaloid (PA) constituents might be teratogenic and hepatotoxic. There is insuff... Read the full pregnancy detail
Breastfeeding Likely Unsafe When used orally. Hepatotoxic pyrrolizidine alkaloid (PA) constituents in gravel root are excreted in milk. There is insufficient reliable information available... 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 Gravel Root? 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. Gravel Root has documented interactions with 2 drug classes — the most serious being cytochrome p450 3a4 (cyp3a4) inducers (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

Gravel Root Does Interact With Other Medications

Gravel Root has 88 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 88 No known interaction 2,742 (incl. Letrozole)
Taking anything else?

Check Another of Your Medications Against Gravel Root

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

What to actually watch for

What Gravel Root Itself Has Been Linked To

This is not an interaction — nothing below involves Letrozole. It is the side-effect record for Gravel Root on its own, from the licensed Natural Medicines monograph. If something new turns up after you add Gravel Root, this list is the first place to look. 2 entries are worth acting on rather than waiting out — marked below.

  • Raised blood pressure Worth acting on Additional detail

    “Orally, gravel root might cause lung damage. The major concern with gravel root use is its pyrrolizidine alkaloid (PA) content. These constituents can cause lung damage with pulmonary-arterial hypertension.”

    Gravel Root · Natural Medicines adverse-effect record, reported in hypertension.

    2 sources cited
    1. 12841. Chojkier M. Hepatic sinusoidal-obstruction syndrome: toxicity of pyrrolizidine alkaloids. J Hepatol 2003;39:437-46. PubMed
    2. 12842. Roeder E. Medicinal plants in Europe containing pyrrolizidine alkaloids. Pharmazie 1995;50:83-98.
  • Liver problems Worth acting on Additional detail

    “Orally, gravel root might cause liver damage. The major concern with gravel root use is its hepatotoxic pyrrolizidine alkaloid (PA) content. Chronic exposure to other plants containing hepatotoxic PA constituents is associated with veno-occlusive disease. Sub-acute veno-occlusive disease can cause vague symptoms, including colicky pains, vomiting, diarrhea, and ascites within several days;”

    Gravel Root · Natural Medicines adverse-effect record, reported in diarrhea.

    3 sources cited
    1. 12841. Chojkier M. Hepatic sinusoidal-obstruction syndrome: toxicity of pyrrolizidine alkaloids. J Hepatol 2003;39:437-46. PubMed
    2. 12842. Roeder E. Medicinal plants in Europe containing pyrrolizidine alkaloids. Pharmazie 1995;50:83-98.
    3. 4021. WHO working group. Pyrrolizidine alkaloids. Environmental Health Criteria, 80. WHO: Geneva, 1988.
  • Diarrhea / Vomiting Additional detail

    “Orally, the major concern with gravel root use is its pyrrolizidine alkaloid (PA) content. These constituents can cause liver and lung injury. Chronic exposure to other plants containing hepatotoxic PA constituents has been associated with veno-occlusive disease. Sub-acute veno-occlusive disease can cause vague symptoms, including colicky pains, vomiting, diarrhea, and ascites within several days;”

    Gravel Root · Natural Medicines adverse-effect record, reported in diarrhea.

    4 sources cited
    1. 12841. Chojkier M. Hepatic sinusoidal-obstruction syndrome: toxicity of pyrrolizidine alkaloids. J Hepatol 2003;39:437-46. PubMed
    2. 12842. Roeder E. Medicinal plants in Europe containing pyrrolizidine alkaloids. Pharmazie 1995;50:83-98.
    3. 4021. WHO working group. Pyrrolizidine alkaloids. Environmental Health Criteria, 80. WHO: Geneva, 1988.
    4. 11990. Stickel F, Seitz HK. The efficacy and safety of comfrey. Public Health Nutr 2000;3:501-8. PubMed

Everything above comes from the Natural Medicines adverse-effect record for Gravel Root — expand a row for the licensed statement it rests on. We read the ADVERSE REACTIONS section of Letrozole’s FDA label too, and the two lists don’t meaningfully overlap — which is why no Letrozole column appears here.

Special populations

Gravel Root in Pregnancy & Breastfeeding

Pregnancy Likely Unsafe

When used orally. Gravel root preparations containing hepatotoxic pyrrolizidine alkaloid (PA) constituents might be teratogenic and hepatotoxic. There is insufficient reliable information available about the safety of using gravel root products that do not contain hepatotoxic PAs during pregnancy.

Lactation Likely Unsafe

When used orally. Hepatotoxic pyrrolizidine alkaloid (PA) constituents in gravel root are excreted in milk. There is insufficient reliable information available about the safety of using gravel root products that do not contain hepatotoxic PAs during 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 Gravel Root 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 Gravel Root 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 Gravel Root 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 Gravel Root as Part of a Dietary Supplement Product? Check It for Interactions

We hold 20 real supplement products containing Gravel Root, each one broken down to its full ingredient list — and combination products often carry several ingredients besides Gravel Root. Even though Gravel Root 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 Gravel Root 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 Gravel Root
Steady interest

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

What is Gravel Root?

  • Kidney stones
  • Urinary tract complaints
  • Fluid retention
  • Gout and joint pain
  • Bladder irritation

Gravel Root is a traditional North American herb long used by herbalists for kidney stones and urinary problems, but there is very little modern scientific evidence to support these uses. Because it contains compounds that may harm the liver and its safety is poorly studied, it should be used with caution, if at all, and avoided in pregnancy and breastfeeding.

Eutrochium purpureum · Asteraceae · Root and rhizome · Tea (decoction), tincture, capsules, dried root

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

Gravel Root: dosing

There is no established or standardized safe dose for Gravel Root. Different products vary widely in strength and quality.If you choose to use it, follow the directions on the product label and keep use short-term. Do not assume that "natural" means safe.

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

Read the full Gravel Root 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 & Gravel Root

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

0Major
88Moderate
0Minor
2,741No known interaction
88 Moderate 2,741 No interaction
Moderate

88 interactions

Showing 60 of 88 moderate interactions — see all 88 on the Gravel Root page.

No interaction 2,741 drugs checked — show the list

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

Showing the 60 most looked-up of 2,741 medications checked with no known interaction — see the full Gravel Root list.

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

Gravel Root References

The 5 references that drive our Gravel Root 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. WHO working group. Pyrrolizidine alkaloids. Environmental Health Criteria, 80. WHO: Geneva, 1988.
  2. Stickel F, Seitz HK. The efficacy and safety of comfrey. Public Health Nutr 2000;3:501-8. PubMed
  3. Chojkier M. Hepatic sinusoidal-obstruction syndrome: toxicity of pyrrolizidine alkaloids. J Hepatol 2003;39:437-46. PubMed
  4. Roeder E. Medicinal plants in Europe containing pyrrolizidine alkaloids. Pharmazie 1995;50:83-98.
  5. Wang YP, Yan J, Fu PP, Chou MW. Human liver microsomal reduction of pyrrolizidine alkaloid N-oxides to form the corresponding carcinogenic parent alkaloid. Toxicol Lett 2005;155:411-20. 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 Gravel Root and Letrozole Together: Common Questions

Is it safe to take Gravel Root with Letrozole?
We do not list a known interaction between Gravel Root 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.
How was the Gravel Root and Letrozole combination checked?
Interactions in our licensed database are recorded against drug classes. Letrozole is filed under 4 classifications, and Gravel Root 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 Gravel Root interact with any other medications?
Yes. Gravel Root has 88 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 — Gravel Root 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

Gravel Root 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 5 citations behind this page Ask a pharmacist Free, personal answer from our licensed team

Still Have a Question About Letrozole and Gravel Root?

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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.