Drug & supplement interaction

Butterbur + Fosphenytoin

Fosphenytoin brand name: Cerebyx.

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

Butterbur has a moderate interaction with Fosphenytoin. Theoretically, CYP3A4 inducers might increase the toxicity of butterbur.

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

Butterbur and Fosphenytoin

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

Moderate

CYTOCHROME P450 3A4 (CYP3A4) INDUCERS

Why this applies to Fosphenytoin

Fosphenytoin falls under CYTOCHROME P450 3A4 (CYP3A4) INDUCERS — the group Butterbur interacts with.

Theoretically, CYP3A4 inducers might increase the toxicity of butterbur.
The pyrrolizidine alkaloid (PA) constituents found in some butterbur products 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

Here's the twist with this pairing: the concern isn't about your fosphenytoin losing strength, it's about the butterbur. Fosphenytoin is a strong CYP3A4 inducer, meaning it revs up that liver enzyme. Some butterbur products still contain pyrrolizidine alkaloids (PAs), and CYP3A4 turns those PAs into toxic byproducts. So speeding up that enzyme could, in theory, increase the liver damage butterbur can cause.

I'll be honest, this is a theoretical worry based on how these compounds behave, not proven cases. The simplest safeguard is to only ever use PA-free (pyrrolizidine alkaloid-free) butterbur products, which sidesteps the problem. Since you're managing seizures, please run any butterbur use by your pharmacist or doctor first.

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

Butterbur Also Interacts With Other Medications

Butterbur has 86 moderate known drug interactions in our database — the Fosphenytoin 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. Fosphenytoin)
Taking anything else?

Check Another of Your Medications Against Butterbur

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

Everything else you take

See Every Supplement That Interacts With Fosphenytoin

This page covers Butterbur only. If you take other supplements — a multivitamin, a sleep aid, something for joints — the Fosphenytoin page lists 205 supplements it has a documented interaction with, worst first, each one explained.

The most serious there right now: 1,4-butanediol (major), American Hellebore (major), Arsenic (major), Beer (major) and Cesium (major).

By severity: 14 major · 172 moderate · 19 minor.

From our pharmacist’s overview on the Fosphenytoin page

“St. John's wort is the entry I would flag first with fosphenytoin (Cerebyx).”

Reviewed by 2 · Jul 18, 2026

Open the Fosphenytoin interaction page

One more smart check

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

We hold 136 real supplement products containing Butterbur, each one broken down to its full ingredient list — and combination products often carry several ingredients besides Butterbur. Your product may carry other ingredients that interact with Fosphenytoin too, on top of Butterbur — 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 Butterbur and Fosphenytoin 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 Butterbur
Top half

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

29 days ago today
Medication Fosphenytoin
Top half

#852 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 Butterbur

What is Butterbur?

  • Migraine prevention
  • Hay fever (allergic rhinitis)
  • Asthma symptoms
  • Stomach and digestive upset
  • Tension headaches

Butterbur is a plant extract most studied for preventing migraines and easing hay fever symptoms, and some standardized products show promise. However, raw or unprocessed butterbur contains compounds that can seriously harm the liver, so only use PA-free (pyrrolizidine alkaloid-free) products, and avoid it during pregnancy and breastfeeding. Talk to your pharmacist or doctor before trying it.

Read the full Butterbur monograph & all interactions
Medication

About Fosphenytoin Injection

What Is Fosphenytoin Injection Used For?

Brand name: Cerebyx

Fosphenytoin injection is used to treat generalized tonic-clonic status epilepticus (a prolonged, life-threatening seizure emergency) and to prevent or treat seizures that occur during or after brain surgery. It is given by intravenous (IV) or intramuscular (IM) injection in a hospital or clinical setting.

It can also be used short-term as a substitute for oral phenytoin when a patient cannot take medicine by mouth. This use is temporary — as soon as oral phenytoin is possible again, it should replace the injection.

See full Fosphenytoin Injection drug information
Keep checking

Other Drugs & Butterbur

Browse every other medication we’ve checked against Butterbur — 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 Butterbur page.

No interaction 2,743 drugs checked — show the list

We also checked Butterbur 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 Butterbur list.

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

Can you take Butterbur with Fosphenytoin?
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 Butterbur and Fosphenytoin 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 Fosphenytoin and Butterbur?

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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.