Drug & supplement interaction

Rehmannia + Phenytoin

Phenytoin brand names: Dilantin Kapseals, Dilantin, Di-Phen, Dilantin Infatabs, Phenytek, and others.

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

We found no known interaction between Rehmannia and Phenytoin 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

Rehmannia and Phenytoin

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 Phenytoin and Rehmannia 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.

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.

Rehmannia safety at a glance

Rehmannia overall Use caution Generally used in traditional medicine, but human safety data are limited and quality varies between products.
Pregnancy Avoid Not enough safety information; best avoided during pregnancy.
Breastfeeding Avoid Not enough safety information; best avoided while breastfeeding.

Safety guidance is general; always confirm with your pharmacist or doctor for your situation.

Still wondering about combining Phenytoin and Rehmannia? Ask Dr. Brian Staiger, PharmD, BCPS directly ›
How we checked

Why No Interaction Is Listed for Phenytoin

Interactions in our licensed database are recorded against drug classes, not just single drug names. Phenytoin is filed under 14 classifications — including cytochrome p450 2c8 (cyp2c8) substrates, cytochrome p450 2c9 (cyp2c9) inducers, anticonvulsants. Rehmannia has documented interactions with 2 drug classes — the most serious being antidiabetes drugs (moderate) and antihypertensive drugs (moderate) — and none of Phenytoin’s classifications are among them.

Classification data comes from our licensed Natural Medicines dataset. A medication can belong to classes beyond those recorded there, so this describes how the check was run — it is not a safety guarantee.

Keep it in perspective

Rehmannia Does Interact With Other Medications

Rehmannia has 258 moderate known drug interactions in our database — Phenytoin isn’t one of them. If you take anything else, check it against the full list below.

Moderate 258 No known interaction 2,572 (incl. Phenytoin)
Taking anything else?

Check Another of Your Medications Against Rehmannia

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

What to actually watch for

What Phenytoin’s Own FDA Label Lists

This is not an interaction — none of it involves Rehmannia. These are the most notable effects listed in the ADVERSE REACTIONS section of Phenytoin’s own FDA label, for the medication by itself. Knowing the drug’s own list makes it easier to work out the likely cause if something new turns up while you take both. 10 of them are worth acting on rather than waiting out — marked below.

  • A change in thyroid levels Worth acting on
  • Unsteadiness Worth acting on
  • High blood sugar Worth acting on
  • Confusion Worth acting on
  • A severe skin reaction Worth acting on
  • Seizures Worth acting on
  • A low platelet count Worth acting on
  • Anemia Worth acting on
  • A severe allergic reaction Worth acting on
  • Hives Worth acting on

Showing the 10 most notable of 25 label-listed effects — ranked by how unusual each one is across medicines generally, with serious effects weighted up.

From the ADVERSE REACTIONS section of the FDA label for Phenytoin. Read the label on DailyMed › Rehmannia’s licensed record lists no adverse effects our clinical vocabulary could match, so there is no Rehmannia side to compare — that is a limit of the record, not a statement that Rehmannia has no side effects.

From our Q&A

Questions About Rehmannia or Phenytoin

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

This page covers Rehmannia only. If you take other supplements — a multivitamin, a sleep aid, something for joints — the Phenytoin page lists 224 supplements it has a documented interaction with, worst first, each one explained.

The most serious there right now: 1,4-butanediol (major), Activated Charcoal (major), Beer (major), Gamma-hydroxybutyrate (ghb) (major) and Kava (major).

By severity: 9 major · 187 moderate · 28 minor.

From our pharmacist’s overview on the Phenytoin page

“Phenytoin (Dilantin) is a seizure medicine with a narrow therapeutic index, meaning small changes in its blood level can bring seizures back or tip over into toxicity, so I treat its supplement list with real seriousness. The biggest group, 78 ingredients, piles on sedation, and alcohol, kava, and GHB all rate major for exactly that re…”

Reviewed by 2 · Jul 18, 2026

Open the Phenytoin interaction page

One more smart check

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

We hold 861 real supplement products containing Rehmannia, each one broken down to its full ingredient list — and combination products often carry several ingredients besides Rehmannia. Even though Rehmannia itself has no known interaction with Phenytoin, 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 Rehmannia and Phenytoin 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 Rehmannia
Top 25%

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

29 days ago today
Medication Phenytoin
Top 25%

#608 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 Rehmannia reference on this page ↓
  • Freshness: we automatically re-check this combination every week — this pair was last verified September 20, 2026. The Rehmannia and Phenytoin records this page draws on were last updated June 22, 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 Rehmannia

What is Rehmannia?

  • Kidney and adrenal support
  • Anemia and blood building (traditional)
  • Inflammatory conditions
  • Allergies
  • Fatigue and aging-related complaints

Rehmannia is a root used for centuries in Traditional Chinese Medicine, often to 'tonify' the kidneys and support energy or blood health. Human evidence for most modern uses is limited, so it should be viewed as unproven rather than reliable. Talk with a pharmacist or doctor before trying it, especially if you are pregnant, breastfeeding, or take other medicines.

Rehmannia glutinosa · Orobanchaceae · Root (raw or steam-prepared) · Dried root, decoctions/teas, capsules, tinctures, and ingredient in multi-herb formulas

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

Rehmannia: dosing

There is no official, well-established standardized dose for Rehmannia. Traditional use varies widely depending on the form (raw versus prepared root), whether it is a tea, capsule, or tincture, and whether it is part of a larger herbal formula.The safest approach is to follow the directions on the product label and not exceed them.

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

Read the full Rehmannia monograph & all interactions
Medication

About Phenytoin

What Is Phenytoin Used For?

Brand names: Dilantin Kapseals, Dilantin, Di-Phen, Dilantin Infatabs, Phenytek, Dilantin injection

Phenytoin is used to treat and prevent seizures. The specific types covered depend on the formulation. Oral extended-release capsules (including Phenytek), chewable tablets (including Dilantin Infatabs and Phenytoin Infatabs), and oral suspension (including Dilantin-125) are used for tonic-clonic (grand mal) and psychomotor (temporal lobe) seizures; most oral forms also cover prevention and treatment of seizures occurring during or after neurosurgery. Chewable tablets and some capsule formulations also cover complex partial seizures.

Parenteral (injectable) phenytoin sodium is used for generalized tonic-clonic status epilepticus (a prolonged, life-threatening seizure emergency) and for prevention and treatment of seizures during neurosurgery. The IV form can also substitute short-term for oral phenytoin when a patient cannot take it by mouth.

Most-Reported Side Effects for Phenytoin

From FAERS, the FDA’s public side-effect reporting system (40,278 reports, all brands). Reports are voluntary and are not proof the drug caused the effect.

Convulsion 3,522 reports
Seizure 3,095 reports
Toxicity to various agents 1,888 reports
Fall 1,604 reports
Dizziness 1,539 reports
See full Phenytoin drug information
Keep checking

Other Drugs & Rehmannia

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

0Major
258Moderate
0Minor
2,571No known interaction
258 Moderate 2,571 No interaction
Moderate

258 interactions

Showing 60 of 258 moderate interactions — see all 258 on the Rehmannia page.

No interaction 2,571 drugs checked — show the list

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

Showing the 60 most looked-up of 2,571 medications checked with no known interaction — see the full Rehmannia list.

See the full Rehmannia interactions page
See every supplement checked against Phenytoin, ranked by severity
Evidence & sources

Rehmannia References

The 3 references that drive our Rehmannia 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. Zhang R, Zhou J, Jia Z, et al. Hypoglycemic effect of Rehmannia glutinosa oligosaccharide in hyperglycemic and alloxan-induced diabetic rats and its mechanism. J Ethnopharmacol 2004;90:39-43. PubMed
  2. Zhang RX, Li MX, Jia ZP. Rehmannia glutinosa: review of botany, chemistry and pharmacology. J Ethnopharmacol 2008;117(2):199-214. PubMed
  3. Chao CH, Hsu JL, Chen MF, et al. Anti-hypertensive effects of Radix Rehmanniae and its active ingredients. Nat Prod Res. 2020;34(11):1547-1552.

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 Rehmannia and Phenytoin Together: Common Questions

Is it safe to take Rehmannia with Phenytoin?
We do not list a known interaction between Rehmannia and Phenytoin. 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.
How was the Rehmannia and Phenytoin combination checked?
Interactions in our licensed database are recorded against drug classes. Phenytoin is filed under 14 classifications, and Rehmannia has documented interactions with 2 drug classes — none of Phenytoin's classifications are among them. A medication can belong to classes beyond those recorded in our dataset, so this describes how the check was run rather than guaranteeing safety.
Does Rehmannia interact with any other medications?
Yes. Rehmannia has 258 documented drug interactions in our database — Phenytoin is simply not one of them. If you take anything else, it is worth checking each one; they are all listed on this page.
Does Phenytoin interact with any supplements?
Yes. Phenytoin has documented interactions with 224 supplements in our database — Rehmannia is not one of them. The Phenytoin 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

Rehmannia monograph Uses, safety profile, and every drug interaction in one place Phenytoin drug information The full plain-English guide to this medication Phenytoin supplement interactions Every supplement checked against Phenytoin, 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 Phenytoin and Rehmannia?

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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.