Drug & supplement interaction

Schisandra + Fosphenytoin Sodium

Fosphenytoin Sodium brand name: Sesquient.

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

Fosphenytoin Sodium falls into 2 drug categories that Schisandra can interact with; the most serious is rated moderate. Theoretically, schisandra might increase the levels and clinical effects of CYP2C19 substrates.

Read the full interaction report
SeverityModerate
LikelihoodProbable
Interactions2
EvidenceD
What do Severity, Likelihood & Evidence mean?
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Interaction report

Schisandra and Fosphenytoin Sodium

These two interact in 2 distinct ways. Each one is explained separately below.

Why Are There 2 Interactions?

Schisandra interacts with whole categories of medication. Fosphenytoin Sodium falls into 2 of those categories, so it can interact with Schisandra in 2 different ways. We’ve listed each one below — your overall risk is driven by the most serious of them (Moderate).

Moderate

CYTOCHROME P450 2C19 (CYP2C19) SUBSTRATES

1 of 2

Why this applies to Fosphenytoin Sodium

Fosphenytoin Sodium falls under CYTOCHROME P450 2C19 (CYP2C19) SUBSTRATES — the group Schisandra interacts with.

Theoretically, schisandra might increase the levels and clinical effects of CYP2C19 substrates.
In vitro research shows that schisandra inhibits CYP2C19, and animal research shows that schisandra increases the concentration of voriconazole, a CYP2C19 substrate. Theoretically, schisandra may also inhibit the metabolism of other CYP2C19 substrates. This effect has not been reported in humans.
Severity Moderate Likelihood Probable Evidence D

Interaction 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..

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

Here's the gist with Sesquient (fosphenytoin). Once it's in your body, fosphenytoin turns into phenytoin, your active seizure medicine. Your liver clears phenytoin partly through an enzyme called CYP2C19. In lab and animal studies, schisandra appears to slow that enzyme down. In theory, that could let phenytoin build up a little higher than usual.

Why does that matter? Phenytoin has a narrow safety window, so even small shifts can tip you from helpful into too much. Signs of higher levels include dizziness, unsteady walking, slurred speech, double vision, drowsiness, or nausea. To be clear, this has only been seen in test tubes and animals, not in people. Still, since this is a finicky drug, please check with your pharmacist or doctor before combining them.

Contact Dr. Brian directly if you have additional questions on this interaction
References
  1. Yuan F, Liang X, Chen X, Qin X, Tan C, Wang L. CYP2C19 is involved in the effect of Wuzhi tablet (Schisandra sphenanthera extract) and its constituents on the pharmacokinetics of intravenous voriconazole. Pharmazie. 2020;75(11):559-564. DOI
Moderate

CYTOCHROME P450 2C9 (CYP2C9) SUBSTRATES

2 of 2

Fosphenytoin Sodium also falls under CYTOCHROME P450 2C9 (CYP2C9) SUBSTRATES.

Theoretically, schisandra might decrease the levels and clinical effects of CYP2C9 substrates.
In vitro and animal research suggests that schisandra induces CYP2C9 enzymes. This effect has not been reported in humans.
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 Schisandra and fosphenytoin (Sesquient). Fosphenytoin is a prodrug that your body converts into phenytoin, a seizure medicine that relies heavily on a liver enzyme called CYP2C9 to be cleared. Lab and animal studies hint that schisandra may speed up that enzyme, which could in theory lower your phenytoin levels and make it work less well.

Phenytoin is what we call a narrow window drug, so even small swings matter. If levels drop too far, seizures could break through. I want to be honest though: this effect has only been seen in test tubes and animals, never confirmed in people, so it's theoretical. Still, before adding schisandra, please check with your pharmacist or neurologist first.

Contact Dr. Brian directly if you have additional questions on this interaction
References
  1. Mu Y, Zhang J, Zhang S, et al. Traditional Chinese medicines Wu Wei Zi (Schisandra chinensis Baill) and Gan Cao (Glycyrrhiza uralensis Fisch) activate pregnane X receptor and increase warfarin clearance in rats. J Pharmacol Exp Ther 2006;316:1369-77. 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

Schisandra Also Interacts With Other Medications

Schisandra has 802 moderate known drug interactions in our database — the Fosphenytoin Sodium one above is among them. If you take anything else, check it against the full list below.

Moderate 802 No known interaction 2,028 (incl. Fosphenytoin Sodium)
Taking anything else?

Check Another of Your Medications Against Schisandra

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

From our Q&A

Questions About Schisandra or Fosphenytoin Sodium

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

This page covers Schisandra only. If you take other supplements — a multivitamin, a sleep aid, something for joints — the Fosphenytoin Sodium page lists 212 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 · 179 moderate · 19 minor.

From our pharmacist’s overview on the Fosphenytoin Sodium page

“Fosphenytoin sodium (Sesquient) converts to phenytoin in the body, and phenytoin is unforgiving about blood levels. A little too low invites seizures, a little too high brings toxicity.”

Reviewed by 2 · Jul 18, 2026

Open the Fosphenytoin Sodium interaction page

One more smart check

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

We hold 2,577 real supplement products containing Schisandra, each one broken down to its full ingredient list — and combination products often carry several ingredients besides Schisandra. Your product may carry other ingredients that interact with Fosphenytoin Sodium too, on top of Schisandra — 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 Schisandra and Fosphenytoin Sodium 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 Schisandra
Top 10%

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

29 days ago today
Medication Fosphenytoin Sodium
Top 25%

#556 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 Schisandra

What is Schisandra?

Schisandra
  • Fatigue and low energy
  • Stress and adaptogen support
  • Liver health
  • Mental focus and performance
  • Menopause symptoms
  • Respiratory complaints

Schisandra is a traditional Chinese medicine berry used as an adaptogen for stress, fatigue, and liver support. Human evidence is limited and most claims are not well proven, but it appears reasonably well tolerated by most healthy adults when used short term. Pregnant and breastfeeding people should avoid it, and anyone with a health condition should check with a pharmacist or doctor first.

Read the full Schisandra monograph & all interactions
Keep checking

Other Drugs & Schisandra

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

0Major
802Moderate
0Minor
2,027No known interaction
802 Moderate 2,027 No interaction
Moderate

802 interactions

Showing 60 of 802 moderate interactions — see all 802 on the Schisandra page.

No interaction 2,027 drugs checked — show the list

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

Showing the 60 most looked-up of 2,027 medications checked with no known interaction — see the full Schisandra list.

See the full Schisandra interactions page
See every supplement checked against Fosphenytoin Sodium, 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
Schisandra monograph › Uses, safety, and every drug interaction in one place Fosphenytoin Sodium supplement interactions › Every supplement checked against Fosphenytoin Sodium, 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 Ask a pharmacist › Free, personal answer from our licensed team
Pharmacist Counseling Corner

Taking Schisandra and Fosphenytoin Sodium Together: Common Questions

Can you take Schisandra with Fosphenytoin Sodium?
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.
Why are there 2 interactions listed for Schisandra and Fosphenytoin Sodium?
Fosphenytoin Sodium belongs to more than one drug category, and Schisandra interacts with each of those categories a little differently. We list every one so nothing is missed — your overall risk is driven by the most serious of them.
How serious is the Schisandra and Fosphenytoin Sodium 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

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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.