Drug & supplement interaction

Tansy Ragwort + Nafcillin

Nafcillin brand name: Nallpen.

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

Tansy Ragwort has a moderate interaction with Nafcillin. Theoretically, CYP3A4 inducers might increase the risk of adverse effects from the pyrrolizidine alkaloid (PA) constituents in tansy ragwort.

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

Tansy Ragwort and Nafcillin

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

Moderate

CYTOCHROME P450 3A4 (CYP3A4) INDUCERS

Why this applies to Nafcillin

Nafcillin falls under CYTOCHROME P450 3A4 (CYP3A4) INDUCERS — the group Tansy Ragwort interacts with.

Theoretically, CYP3A4 inducers might increase the risk of adverse effects from the pyrrolizidine alkaloid (PA) constituents in tansy ragwort.
Tansy ragwort contains PAs. PAs are substrates of CYP3A4. Theoretically, drugs that induce CYP3A4 might increase the conversion of PAs to toxic metabolites.
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

Let me be straight with you up front: tansy ragwort is something you should not be taking internally at all. It contains pyrrolizidine alkaloids, plant chemicals that can seriously injure your liver. So my main concern here isn't really about your antibiotic working better or worse, it's about the herb itself.

Here's the wrinkle with nafcillin. Nafcillin speeds up a liver enzyme called CYP3A4, and that same enzyme is what turns tansy ragwort's alkaloids into their toxic, liver-damaging forms. So in theory, nafcillin could ramp up that conversion and make the herb more harmful to your liver. I want to be honest that this is theoretical, based mostly on lab and animal work, not human cases. Still, the safe move is simple: skip the tansy ragwort entirely, and check with your pharmacist or doctor before any herbal product.

Contact Dr. Brian directly if you have additional questions on this interaction
References
  1. Chojkier M. Hepatic sinusoidal-obstruction syndrome: toxicity of pyrrolizidine alkaloids. J Hepatol 2003;39:437-46. PubMed
  2. 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

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

Tansy Ragwort Also Interacts With Other Medications

Tansy Ragwort has 86 moderate known drug interactions in our database — the Nafcillin one above is one of them. If you take anything else, check it against the full list below.

Moderate 86 No known interaction 2,744 (incl. Nafcillin)
Taking anything else?

Check Another of Your Medications Against Tansy Ragwort

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

Everything else you take

See Every Supplement That Interacts With Nafcillin

This page covers Tansy Ragwort only. If you take other supplements — a multivitamin, a sleep aid, something for joints — the Nafcillin page lists 58 supplements it has a documented interaction with, worst first, each one explained.

The most serious there right now: Asarabacca (major), Siberian Cocklebur (major), Alkanna (moderate), Alpine Ragwort (moderate) and Aristolochia (moderate).

By severity: 2 major · 54 moderate · 2 minor.

From our pharmacist’s overview on the Nafcillin page

“Anyone on nafcillin (Nallpen) is usually fighting a serious staph infection, and that makes this a time to be genuinely careful with supplements. Of the 58 with a known interaction on file, the two rated major, Siberian cocklebur and asarabacca, both stress the kidneys and could compound damage while you are being treated.”

Reviewed by 2 · Jul 18, 2026

Open the Nafcillin interaction page

How much people look this up

Where Tansy Ragwort and Nafcillin 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 Tansy Ragwort
Steady interest

#1,036 of 1,452 supplements looked up here in the last 7 days

29 days ago today
Medication Nafcillin
Steady interest

#2,767 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 Tansy Ragwort

What is Tansy Ragwort?

  • Traditional wound and skin washes
  • Folk remedy for sore throat (gargle)
  • Topical poultice for joint or muscle aches
  • Historical use for menstrual complaints

Tansy ragwort is a toxic weed that contains pyrrolizidine alkaloids, which can seriously damage the liver. It is not recommended as a supplement or home remedy, and there is no reliable evidence that it safely treats any condition. Avoid taking it internally and talk to a pharmacist or doctor before using any herbal product.

Read the full Tansy Ragwort monograph & all interactions
Medication

About Nafcillin Injection

What Is Nafcillin Injection Used For?

Brand name: Nallpen

NAFCILLIN Injection is used to treat infections caused by staphylococci — specifically strains that produce an enzyme called penicillinase, which makes them resistant to regular penicillin. Susceptibility testing is performed to confirm the bacteria will respond to nafcillin before or shortly after starting treatment.

Nafcillin may also be started right away when a resistant staph infection is strongly suspected, even before test results are available. It should not be used for infections caused by bacteria that would respond to standard penicillin G, or for infections caused by non-staph organisms.

See full Nafcillin Injection drug information
Keep checking

Other Drugs & Tansy Ragwort

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

0Major
86Moderate
0Minor
2,743No known interaction
86 Moderate 2,743 No interaction
Moderate

86 interactions

Showing 60 of 86 moderate interactions — see all 86 on the Tansy Ragwort page.

No interaction 2,743 drugs checked — show the list

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

Showing the 60 most looked-up of 2,743 medications checked with no known interaction — see the full Tansy Ragwort list.

See the full Tansy Ragwort interactions page
See every supplement checked against Nafcillin, 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
Tansy Ragwort monograph › Uses, safety, and every drug interaction in one place Nafcillin supplement interactions › Every supplement checked against Nafcillin, ranked by severity Nafcillin Injection 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 Tansy Ragwort and Nafcillin Together: Common Questions

Can you take Tansy Ragwort with Nafcillin?
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 Tansy Ragwort and Nafcillin 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 Nafcillin and Tansy Ragwort?

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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.