Drug & supplement interaction

American Elder + Fostamatinib

Fostamatinib brand name: Tavalisse.

Moderate Interaction
Medically reviewed by · Updated September 2026
The bottom line Moderate

American Elder has a moderate interaction with Fostamatinib. Theoretically, taking American elder might increase levels of CYP3A4 substrates.

Read the full interaction report
SeverityModerate
LikelihoodPossible
EvidenceD
What do Severity, Likelihood & Evidence mean?
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Interaction report

American Elder and Fostamatinib

Here is the interaction we found between these two, with the evidence behind it.

Moderate

CYTOCHROME P450 3A4 (CYP3A4) SUBSTRATES

Why this applies to Fostamatinib

Fostamatinib falls under CYTOCHROME P450 3A4 (CYP3A4) SUBSTRATES — the group American Elder interacts with.

Theoretically, taking American elder might increase levels of CYP3A4 substrates.
In vitro research shows that American elder inhibits CYP3A4 enzymes.
Severity Moderate Likelihood Possible Evidence D

Interaction has been documented in animal or in lab research, or the interaction has been documented in humans but is limited to case reports or conflicting clinical research exists.

Dr. Brian Staiger, PharmD, BCPS
Dr. Brian Staiger explains PharmD, Clinical Pharmacist

Here's the situation with elderberry and your Fostamatinib (Tavalisse). Your body relies on a liver enzyme called CYP3A4 to help clear the active form of this medication. Lab tests suggest American elder may slow that enzyme down a bit. If that happened in a real person, the drug could build up slightly, which might raise the chance of side effects like high blood pressure, diarrhea, nausea, dizziness, or changes in your liver tests.

I want to be honest, though: this is only a theoretical concern based on test-tube research, not real patient studies, so the risk is uncertain. Cooked elderberry in normal food amounts is unlikely to matter much, but concentrated supplements are a different story. Just check with your pharmacist or doctor before adding it.

Contact Dr. Brian directly if you have additional questions on this interaction
References
  1. Budzinski JW, Foster BC, Vandenhoek S, Arnason JT. An in vitro evaluation of human cytochrome P450 3A4 inhibition by selected commercial herbal extracts and tinctures. Phytomedicine 2000;7:273-82. PubMed

What These Ratings Mean

Every interaction above is graded three ways — here’s the key to each label.

Severity how clinically significant the interaction is
Major

Clinically significant. Avoid the combination, or use only under close professional supervision.

Moderate

Usually worth avoiding or managing — may need monitoring, a dose change, or timing apart.

Minor

Generally not serious. Be aware of it and mention it to your pharmacist.

Likelihood how strong the evidence is that the interaction actually happens in people
  • LikelyWell-controlled human studies have demonstrated the likely existence of this interaction.
  • ProbableInteraction has not been documented in well-controlled studies, however, the interaction has been demonstrated in some small human studies or in controlled animal studies in conjunction with multiple case reports.
  • PossibleInteraction has been documented in animal or in lab research, or the interaction has been documented in humans but is limited to case reports or conflicting clinical research exists.
  • UnlikelyInteraction has been demonstrated in animal or in lab research but has been shown not to occur in humans.
Evidence the quality of the studies behind the rating (graded A–D)
  • AHigh-quality meta-analysis (quantitative systematic review).
  • BCase-control study.
  • CConsensus.
  • DAnecdotal evidence.

These ratings are for information only. Never start, stop, or otherwise change your therapy before speaking with your provider.

Keep it in perspective

American Elder Also Interacts With Other Medications

American Elder has 643 moderate known drug interactions in our database — the Fostamatinib one above is one of them. If you take anything else, check it against the full list below.

Moderate 643 No known interaction 2,187 (incl. Fostamatinib)
Taking anything else?

Check Another of Your Medications Against American Elder

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

Everything else you take

See Every Supplement That Interacts With Fostamatinib

This page covers American Elder only. If you take other supplements — a multivitamin, a sleep aid, something for joints — the Fostamatinib page lists 209 supplements it has a documented interaction with, worst first, each one explained.

The most serious there right now: Activated Charcoal (major), Beer (major), Grapefruit (major), Siberian Cocklebur (major) and St. John's Wort (major).

By severity: 6 major · 167 moderate · 36 minor.

From our pharmacist’s overview on the Fostamatinib page

“I would treat the supplement list for fostamatinib (Tavalisse), a medicine that raises platelet counts in chronic immune thrombocytopenia, with real care. Most of what shows up here involves CYP3A4, the liver enzyme that clears fostamatinib, so grapefruit can drive its blood level up while St.”

Reviewed by 2 · Jul 18, 2026

Open the Fostamatinib interaction page

One more smart check

Taking American Elder as Part of a Dietary Supplement Product? Check It for Interactions

We hold 61 real supplement products containing American Elder, each one broken down to its full ingredient list — and combination products often carry several ingredients besides American Elder. Your product may carry other ingredients that interact with Fostamatinib too, on top of American Elder — and those would not show on this page. Find your product and we’ll check every ingredient on its label:

How much people look this up

Where American Elder and Fostamatinib 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 American Elder
Top half

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

29 days ago today
Medication Fostamatinib
Steady interest

#1,850 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.

Supplement

About American Elder

What is American Elder?

American Elder
  • Cold and flu symptoms
  • Immune support
  • Fever and congestion (traditional)
  • Constipation (traditional)
  • Antioxidant support

American elder is a North American plant whose cooked, ripe berries and flowers are used mainly for colds, flu, and general immune support. The science behind these uses is limited and most studies focus on the closely related European black elder (Sambucus nigra), so benefits are uncertain. Only properly prepared berries and flowers should be used, since raw berries, leaves, bark, and seeds can cause poisoning.

Read the full American Elder monograph & all interactions
Medication

About Fostamatinib

What Is Fostamatinib Used For?

Brand name: Tavalisse

Tavalisse (fostamatinib) is used to treat thrombocytopenia — dangerously low platelet counts — in adults with chronic immune thrombocytopenia (ITP). It is specifically for people whose platelet counts have not improved enough with at least one earlier ITP treatment.

The goal is to raise platelet counts high enough to reduce the risk of serious bleeding. If platelet counts do not respond sufficiently after 12 weeks, the medication is typically stopped.

See full Fostamatinib drug information
Keep checking

Other Drugs & American Elder

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

0Major
643Moderate
0Minor
2,186No known interaction
643 Moderate 2,186 No interaction
Moderate

643 interactions

Showing 60 of 643 moderate interactions — see all 643 on the American Elder page.

No interaction 2,186 drugs checked — show the list

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

Showing the 60 most looked-up of 2,186 medications checked with no known interaction — see the full American Elder list.

See the full American Elder interactions page
See every supplement checked against Fostamatinib, ranked by severity
Sources

Sources & How We Checked

Interaction details are evidence-graded and sourced from the Natural Medicines database. The medication overview comes from MedlinePlus.

Content is written and reviewed by licensed HelloPharmacist pharmacists. See our data sources and editorial standards for how this information is built and checked.

Parts of this content are provided by the Therapeutic Research Center, LLC.

DISCLAIMER: Currently this does not check for drug-drug interactions. This is not an all-inclusive comprehensive list of potential interactions and is for informational purposes only. Not all interactions are known or well-reported in the scientific literature, and new interactions are continually being reported. Input is needed from a qualified healthcare provider including a pharmacist before starting any therapy. Application of clinical judgment is necessary.

© 2021 Therapeutic Research Center, LLC

Keep exploring
American Elder monograph › Uses, safety, and every drug interaction in one place Fostamatinib supplement interactions › Every supplement checked against Fostamatinib, ranked by severity Fostamatinib drug information › The full plain-English guide to this medication Supplement interaction checker › Check any supplement or product against your medications Browse medications A–Z › Every drug we've checked against herbs & supplements Ask a pharmacist › Free, personal answer from our licensed team
Pharmacist Counseling Corner

Taking American Elder and Fostamatinib Together: Common Questions

Can you take American Elder with Fostamatinib?
There is a moderate interaction, so it may be acceptable with monitoring or timing changes — but check with your pharmacist first. Read the full details on this page and confirm with your pharmacist before combining them.
How serious is the American Elder and Fostamatinib interaction?
We rate it Moderate. This combination may require monitoring, a dose adjustment, or separating the times you take each one. Consult your pharmacist before using them together.

Written and reviewed by the HelloPharmacist editorial staff. Our editorial policy

Still Have a Question About Fostamatinib and American Elder?

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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.