Drug & supplement interaction

Black Walnut + Ondansetron

Ondansetron brand name: Zofran.

No Known Interaction
Medically reviewed by · Updated July 2026 · Pair last verified Sep 20, 2026
The bottom line No known interaction

We found no known interaction between Black Walnut and Ondansetron 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

Black Walnut and Ondansetron

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 Ondansetron and Black Walnut 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.

Worth understanding: our licensed dataset holds no drug-interaction record for Black Walnut at all — not against Ondansetron, and not against any other medication we track. This verdict therefore rests on the absence of any recorded data, not on research that looked at this combination and found nothing. We cannot rule an interaction out.

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.

Black Walnut safety at a glance

Black Walnut overall Use caution May be acceptable short-term for most adults, but human safety data are limited and long-term use is not well studied.
Pregnancy Likely Safe When the fruit (nut) is consumed in amounts normally found in foods. Read the full pregnancy detail
Breastfeeding Likely Safe When the fruit (nut) is consumed in amounts normally found in foods. 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 Ondansetron and Black Walnut? Ask Dr. Brian Staiger, PharmD, BCPS directly ›
What to actually watch for

What Black Walnut Itself Has Been Linked To

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

  • A severe allergic reaction Worth acting on Additional detail

    “Orally, black walnut fruit (nut) is well tolerated. However, the leaf, bark, and hull of black walnut contain high quantities of tannins, which may cause adverse effects when used orally or topically.

    Most Common Adverse Effects:

    Orally: The leaf, bark, and hull can cause gastrointestinal upset.

    Topically: Hull preparations may cause a temporary yellow or brown discoloration at the site of application.”

    Black Walnut · Natural Medicines adverse-effect record, reported in cancer.

  • An allergic reaction Worth acting on Additional detail

    “Tree nuts, which include black walnuts, can cause allergic reactions in sensitive individuals. Due to the prevalence of this allergy in the general population, tree nuts are classified as a major food allergen in the United States.”

    Black Walnut · Natural Medicines adverse-effect record, reported in allergic rhinitis (hay fever).

    1 source cited
    1. 105410. Food and Drug Administration. Food Allergen Labeling and Consumer Protection Act of 2004 (FALCPA); Public Law 108-282, Title II. Accessed on May 19, 2021. Available at: https://www.fda.gov/food/food-allergensgluten-free-guidance-documents-regulatory-infor
  • Stomach upset Additional detail

    “Orally, black walnut leaf, bark, or hull may cause gastrointestinal upset due to tannin content (12). Also, daily use of the juglone-containing bark of a related species (English walnut) is associated with increased risk of tongue cancer and lip leukoplakia (2,12).”

    Black Walnut · Natural Medicines adverse-effect record, reported in cancer.

    2 sources cited
    1. 12. McGuffin M, Hobbs C, Upton R, Goldberg A, eds. American Herbal Products Association's Botanical Safety Handbook. Boca Raton, FL: CRC Press, LLC 1997.
    2. 2. Blumenthal M, ed. The Complete German Commission E Monographs: Therapeutic Guide to Herbal Medicines. Trans. S. Klein. Boston, MA: American Botanical Council, 1998.

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

Special populations

Black Walnut in Pregnancy & Breastfeeding

Pregnancy And Lactation Likely Safe

When the fruit (nut) is consumed in amounts normally found in foods.

Pregnancy And Lactation Possibly Unsafe

When the bark is used orally or topically; avoid using. There is insufficient reliable information available about the safety of black walnut leaf or hull when used orally in medicinal amounts during pregnancy or lactation; avoid using.

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 Black Walnut or Ondansetron

These are real questions from readers, answered by the pharmacists at HelloPharmacist — written by a person, not generated from a database. Each one covers Black Walnut or Ondansetron, 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 Ondansetron

This page covers Black Walnut only. If you take other supplements — a multivitamin, a sleep aid, something for joints — the Ondansetron page lists 195 supplements it has a documented interaction with, worst first, each one explained.

The most serious there right now: Activated Charcoal (major), Grapefruit (major), Lithium (major), St. John's Wort (major) and 1,3-dmaa (moderate).

By severity: 4 major · 145 moderate · 46 minor.

From our pharmacist’s overview on the Ondansetron page

“Ondansetron (Zofran) often stands between you and relentless nausea from chemotherapy or surgery, so read this page carefully. Four of the 195 ingredients rate major.”

Reviewed by 2 · Jul 18, 2026

Open the Ondansetron interaction page

One more smart check

Taking Black Walnut as Part of a Dietary Supplement Product? Check It for Interactions

We hold 863 real supplement products containing Black Walnut, each one broken down to its full ingredient list — and combination products often carry several ingredients besides Black Walnut. Even though Black Walnut itself has no known interaction with Ondansetron, 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 Black Walnut and Ondansetron 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 Black Walnut
Top 25%

#220 of 1,452 supplements looked up here in the last 7 days

29 days ago today
Medication Ondansetron
Steady interest

#2,073 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 Black Walnut reference on this page ↓
  • Freshness: we automatically re-check this combination every week — this pair was last verified September 20, 2026. The Black Walnut and Ondansetron 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 Black Walnut

What is Black Walnut?

  • Intestinal parasites and worms
  • Digestive complaints
  • Antimicrobial and antifungal support
  • Skin and topical washes
  • Laxative or 'cleanse' products

Black walnut is a tree whose green hulls are traditionally used as a natural antiparasitic and digestive remedy, but solid human evidence for these uses is lacking. It contains a compound called juglone that may be irritating, so use it cautiously, avoid long-term use, and check with your pharmacist or doctor first.

Juglans nigra · Juglandaceae · Hulls (the green outer covering of the nut), bark, leaves, and nut · Capsules, tinctures, liquid extracts, powders, and teas

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

Black Walnut: dosing

There is no well-established, standardized dose for black walnut. The amount of active compounds varies a lot between products and forms (capsule, tincture, or tea), which makes consistent dosing difficult.If you choose to use it, follow the directions on the product label and do not exceed them.

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

Read the full Black Walnut monograph & all interactions
Medication

About Ondansetron

What Is Ondansetron Used For?

Brand name: Zofran

Ondansetron is used to prevent nausea and vomiting in several situations. Oral forms (tablets, orally disintegrating tablets, and oral solution) are approved to prevent nausea and vomiting from highly or moderately emetogenic (nausea-causing) cancer chemotherapy, from radiation therapy to the abdomen or whole body, and from surgery.

Ondansetron injection (given intravenously or intramuscularly in a clinical setting) is approved to prevent nausea and vomiting from emetogenic cancer chemotherapy — including high-dose cisplatin — in adults and children as young as 6 months old, as well as to prevent postoperative nausea and vomiting.

Most-Reported Side Effects for Ondansetron

From FAERS, the FDA’s public side-effect reporting system (121,840 reports, all brands). Reports are voluntary and are not proof the drug caused the effect.

Nausea 14,459 reports
Fatigue 10,275 reports
Diarrhea 9,488 reports
Vomiting 8,777 reports
Dyspnea 5,971 reports
See full Ondansetron drug information
Keep checking

Other Drugs & Black Walnut

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

0Major
0Moderate
0Minor
2,829No known interaction
2,829 No interaction
No interaction 2,829 drugs checked — show the list

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

Showing the 60 most looked-up of 2,829 medications checked with no known interaction — see the full Black Walnut list.

See the full Black Walnut interactions page
See every supplement checked against Ondansetron, ranked by severity
Evidence & sources

Black Walnut References

The 3 references that drive our Black Walnut 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. McGuffin M, Hobbs C, Upton R, Goldberg A, eds. American Herbal Products Association's Botanical Safety Handbook. Boca Raton, FL: CRC Press, LLC 1997.
  3. Food and Drug Administration. Food Allergen Labeling and Consumer Protection Act of 2004 (FALCPA); Public Law 108-282, Title II. Accessed on May 19, 2021. Available at: https://www.fda.gov/food/food-allergensgluten-free-guidance-documents-regulatory-infor

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 Black Walnut and Ondansetron Together: Common Questions

Is it safe to take Black Walnut with Ondansetron?
We do not list a known interaction between Black Walnut and Ondansetron. 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.
Does Ondansetron interact with any supplements?
Yes. Ondansetron has documented interactions with 195 supplements in our database — Black Walnut is not one of them. The Ondansetron 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

Black Walnut monograph Uses, safety profile, and every drug interaction in one place Ondansetron drug information The full plain-English guide to this medication Ondansetron supplement interactions Every supplement checked against Ondansetron, 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 3 citations behind this page Ask a pharmacist Free, personal answer from our licensed team

Still Have a Question About Ondansetron and Black Walnut?

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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.