Drug & supplement interaction

Spiny Restharrow + Letrozole

Letrozole brand name: Femara.

No Known Interaction
Medically reviewed by · Updated June 2026 · Pair last verified Sep 13, 2026
The bottom line No known interaction

We found no known interaction between Spiny Restharrow 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

Spiny Restharrow 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 Spiny Restharrow 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.

Spiny Restharrow safety at a glance

Spiny Restharrow overall Use caution Generally regarded as traditionally used, but human safety data are limited.
Pregnancy Avoid Not enough safety information, so it is best avoided during pregnancy.
Breastfeeding Avoid Safety while breastfeeding is unknown, so avoid use.

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

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

Spiny Restharrow Does Interact With Other Medications

Spiny Restharrow has 1 moderate known drug interaction in our database — Letrozole isn’t one of them. If you take anything else, check it against the full list below.

Moderate 1 No known interaction 2,829 (incl. Letrozole)
Taking anything else?

Check Another of Your Medications Against Spiny Restharrow

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

What to actually watch for

What Letrozole’s Own FDA Label Lists

This is not an interaction — none of it involves Spiny Restharrow. These are the most notable effects listed in the ADVERSE REACTIONS section of Letrozole’s own FDA label, for the medication by itself. Knowing the drug’s own list makes it easier to work out the likely cause if something new turns up while you take both. One of them is worth acting on rather than waiting out — marked below.

  • Bleeding or bruising Worth acting on
  • Flushing
  • Sweating
  • Joint pain
  • Muscle pain
  • Swelling
  • Tiredness
  • Dizziness
  • Headache
  • Nausea

From the ADVERSE REACTIONS section of the FDA label for Letrozole. Read the label on DailyMed › Spiny Restharrow’s licensed record lists no adverse effects our clinical vocabulary could match, so there is no Spiny Restharrow side to compare — that is a limit of the record, not a statement that Spiny Restharrow has no side effects.

From our Q&A

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

We hold 17 real supplement products containing Spiny Restharrow, each one broken down to its full ingredient list — and combination products often carry several ingredients besides Spiny Restharrow. Even though Spiny Restharrow 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 Spiny Restharrow 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 Spiny Restharrow
Steady interest

#746 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 Spiny Restharrow reference on this page ↓
  • Freshness: we automatically re-check this combination every week — this pair was last verified September 13, 2026. The Spiny Restharrow and Letrozole records this page draws on were last updated June 22, 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 Spiny Restharrow

What is Spiny Restharrow?

  • Increasing urine flow (mild diuretic)
  • Flushing the urinary tract
  • Mild bladder and kidney complaints
  • Fluid retention
  • Traditional support for skin and joint complaints

Spiny Restharrow is a traditional European herb whose root has long been used as a mild diuretic to help flush the urinary tract. Solid human evidence for its benefits is very limited, so any effect remains unproven. If you want to try it, talk with a pharmacist or doctor first, especially if you have kidney, heart, or fluid-balance concerns.

Ononis spinosa · Fabaceae · Root (and sometimes the aerial/flowering parts) · Tea (dried root), tinctures, liquid extracts, capsules

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

Spiny Restharrow: dosing

There is no well-established standardized dose for Spiny Restharrow. Traditional use mainly involves a tea made from the dried root, but exact amounts vary widely between products and references.The safest approach is to follow the directions on the product label and not exceed them.

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

Read the full Spiny Restharrow 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 & Spiny Restharrow

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

0Major
1Moderate
0Minor
2,828No known interaction
1 Moderate 2,828 No interaction
Moderate

1 interaction

No interaction 2,828 drugs checked — show the list

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

Showing the 60 most looked-up of 2,828 medications checked with no known interaction — see the full Spiny Restharrow list.

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

Spiny Restharrow References

The 2 references that drive our Spiny Restharrow 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. Gruenwald J, Brendler T, Jaenicke C. PDR for Herbal Medicines. 1st ed. Montvale, NJ: Medical Economics Company, Inc., 1998.

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 Spiny Restharrow and Letrozole Together: Common Questions

Is it safe to take Spiny Restharrow with Letrozole?
We do not list a known interaction between Spiny Restharrow 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 Spiny Restharrow and Letrozole combination checked?
Interactions in our licensed database are recorded against drug classes. Letrozole is filed under 4 classifications, and Spiny Restharrow 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 Spiny Restharrow interact with any other medications?
Yes. Spiny Restharrow has 1 documented drug interaction 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 — Spiny Restharrow 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

Spiny Restharrow 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 2 citations behind this page Ask a pharmacist Free, personal answer from our licensed team

Still Have a Question About Letrozole and Spiny Restharrow?

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.