Drug & supplement interaction

Kava + Phenytoin

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

Major Interaction
Medically reviewed by · Updated October 2026
The bottom line Major

Phenytoin falls into 4 drug categories that Kava can interact with; the most serious is rated major. Combining kava with CNS depressants can have additive sedative effects.

Read the full interaction report
SeverityMajor
LikelihoodProbable
Interactions4
EvidenceA
What do Severity, Likelihood & Evidence mean?
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Interaction report

Kava and Phenytoin

These two interact in 4 distinct ways. Each one is explained separately below.

Why Are There 4 Interactions?

Kava interacts with whole categories of medication. Phenytoin falls into 4 of those categories, so it can interact with Kava in 4 different ways. We’ve listed each one below — your overall risk is driven by the most serious of them (Major).

Major

CNS DEPRESSANTS

1 of 4

Why this applies to Phenytoin

Phenytoin falls under CNS DEPRESSANTS — the group Kava interacts with.

Combining kava with CNS depressants can have additive sedative effects.
Kava has CNS depressant effects. Concomitant use of kava with other CNS depressants can increase the risk of drowsiness and motor reflex depression. Clinical practice guidelines from a joint taskforce of the World Federation of Societies of Biological Psychiatry (WFSBP) and the Canadian Network for Mood and Anxiety Treatments (CANMAT) recommend that CNS depressants, including alcohol and benzodiazepines, not be used with kava.
Severity Major Likelihood Probable Evidence A

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 thing to keep in mind if you take phenytoin (Dilantin) for seizures and you're thinking about kava. Both of these can calm down the nervous system, so stacking them together can pile on the sedation. That means you may feel extra drowsy, dizzy, foggy, unsteady on your feet, or slower to react. For older folks especially, that wobbliness can raise the risk of a fall.

There's also a second reason for caution: phenytoin can be hard on the liver, and kava has been tied to rare but serious liver damage, so combining them isn't ideal. This is a well-supported, major interaction, so please don't add kava without first checking with your pharmacist or doctor. Never change your phenytoin on your own.

Contact Dr. Brian directly if you have additional questions on this interaction
References
  1. Pittler MH, Ernst E. Efficacy of kava extract for treating anxiety: systematic review and meta-analysis. J Clin Psychopharmacol 2000;20:84-9. PubMed
  2. Munte TF, Heinze HJ, Matzke M, Steitz J. Effects of oxazepam and an extract of kava roots (Piper methysticum) on event-related potentials in a word recognition task. Neuropsychobiology 1993;27:46-53.
  3. Cairney S, Maruff P, Clough AR, et al. Saccade and cognitive impairment associated with kava intoxication. Hum Psychopharmacol 2003;18:525-33. PubMed
  4. Sarris J, Kavanagh DJ, Byrne G, et al. The Kava Anxiety Depression Spectrum Study (KADSS): a randomized, placebo-controlled crossover trial using an aqueous extract of Piper methysticum. Psychopharmacology 2009;205:399-407. PubMed
  5. Sarris J, Ravindran A, Yatham LN, et al. Clinician guidelines for the treatment of psychiatric disorders with nutraceuticals and phytoceuticals: The World Federation of Societies of Biological Psychiatry (WFSBP) and Canadian Network for Mood and Anxiety T
Moderate

CYTOCHROME P450 2C19 (CYP2C19) SUBSTRATES

2 of 4

Phenytoin also falls under CYTOCHROME P450 2C19 (CYP2C19) SUBSTRATES.

Theoretically, kava might increase levels of CYP2C19 substrates.
In vitro research shows that kava significantly inhibits CYP2C19 enzymes. This effect has not yet 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 idea behind pairing kava with your phenytoin (Dilantin). Phenytoin is partly cleared by a liver enzyme called CYP2C19. In test-tube studies, kava appears to slow that enzyme down. If that happened in the body, phenytoin could build up and push your blood levels higher than intended.

Why that matters: phenytoin has a narrow safe range, so even small jumps can cause trouble like dizziness, unsteady walking, slurred speech, double vision, drowsiness, or nausea. I want to be honest though, this concern comes only from lab research and hasn't been confirmed in people, so it's theoretical right now. Kava also carries its own liver risks, which is another reason to be cautious. Please don't change anything on your own. Check with your pharmacist or doctor before adding kava.

Contact Dr. Brian directly if you have additional questions on this interaction
References
  1. Mathews JM, Etheridge AS, Black SR. Inhibition of human cytochrome P450 activities by kava extract and kavalactones. Drug Metab Dispos 2002;30:1153-7. PubMed
  2. Unger M, Frank A. Simultaneous determination of the inhibitory potency of herbal extracts on the activity of six major cytochrome P450 enzymes using liquid chromatography/mass spectrometry and automated online extraction. Rapid Commun Mass Spectrom 2004;1 PubMed
Moderate

HEPATOTOXIC DRUGS

3 of 4

Phenytoin also falls under HEPATOTOXIC DRUGS.

Theoretically, using kava with hepatotoxic drugs might increase the risk of liver damage.
Kava has been linked with over 100 cases of hepatotoxicity. Most cases occur with excessive and prolonged use. There is some concern that kava can adversely affect the liver, especially when used in combination with hepatotoxic drugs.
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 concern with pairing kava and phenytoin (Dilantin): both can be tough on your liver. Phenytoin is known to occasionally raise liver enzymes or, rarely, cause liver injury. Kava has been tied to over 100 reports of liver problems, mostly with heavy or long-term use. Stacking two liver stressors together may add up.

To be clear, this is a theoretical concern based on case reports, not strong proof. But because liver trouble can sneak up quietly, it's worth watching for warning signs like yellowing skin or eyes, dark urine, belly pain, or unusual tiredness. Please don't change your phenytoin on your own. Just check with your pharmacist or doctor before adding kava, especially if your liver isn't perfectly healthy.

Contact Dr. Brian directly if you have additional questions on this interaction
References
  1. Escher M, Desmeules J, Giostra E, Mentha G. Hepatitis associated with Kava, a herbal remedy for anxiety. BMJ 2001;322:139.
  2. Russmann S, Lauterburg BH, Helbling A. Kava hepatotoxicity [letter]. Ann Intern Med 2001;135:68-9.
  3. Liver Toxicity With Kava. Pharmacist's Letter/Prescriber's Letter. January 2001.
  4. Consultation letter MLX 286: Proposals to prohibit the herbal ingredient Kava-Kava (Piper methysticum) in unlicensed medicines. Medicines Control Agency, United Kingdom, July 19, 2002.
  5. Li XZ, Ramzan I. Role of ethanol in kava hepatotoxicity. Phytother Res 2010;24:475-80. PubMed
  6. Chanwai, L. G. Kava toxicity. Emergency Medicine 2002;12:142-145.
Moderate

CYTOCHROME P450 2C9 (CYP2C9) SUBSTRATES

4 of 4

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

Theoretically, kava might increase levels of CYP2C9 substrates.
In vitro research shows that kava significantly inhibits CYP2C9 enzymes. This effect has not yet 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 gist with phenytoin and kava. Your body relies on a liver enzyme called CYP2C9 to clear phenytoin out of your system. In lab studies (test tube only, not yet shown in real people), kava appears to slow that enzyme down. If that happened in your body, phenytoin could build up to higher levels than usual.

Why does that matter? Phenytoin has a narrow safe range, so even small shifts can tip you into side effects like dizziness, unsteady walking, slurred speech, double vision, or drowsiness. Kava can also stress the liver, which adds another reason for caution. Right now this is theoretical, but please loop in your pharmacist or doctor before combining them.

Contact Dr. Brian directly if you have additional questions on this interaction
References
  1. Mathews JM, Etheridge AS, Black SR. Inhibition of human cytochrome P450 activities by kava extract and kavalactones. Drug Metab Dispos 2002;30:1153-7. PubMed
  2. Unger M, Frank A. Simultaneous determination of the inhibitory potency of herbal extracts on the activity of six major cytochrome P450 enzymes using liquid chromatography/mass spectrometry and automated online extraction. Rapid Commun Mass Spectrom 2004;1 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

Kava Also Interacts With Other Medications

Kava has 247 major, 581 moderate, 338 minor known drug interactions in our database — the Phenytoin one above is among them. If you take anything else, check it against the full list below.

Major 247 Moderate 581 Minor 338 No known interaction 1,664 (incl. Phenytoin)
Taking anything else?

Check Another of Your Medications Against Kava

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

From our Q&A

Questions About Kava 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 Kava 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 Kava 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 L-tryptophan (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 Kava as Part of a Dietary Supplement Product? Check It for Interactions

We hold 403 real supplement products containing Kava, each one broken down to its full ingredient list — and combination products often carry several ingredients besides Kava. Your product may carry other ingredients that interact with Phenytoin too, on top of Kava — 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 Kava 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 Kava
Top 25%

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

29 days ago today
Medication Phenytoin
Top 25%

#534 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 Kava

What is Kava?

Kava
  • Anxiety and stress
  • Restlessness
  • Trouble sleeping
  • Relaxation in social or cultural settings
  • Menopausal symptoms

Kava is a Pacific Island plant traditionally used to promote relaxation and ease anxiety, and some studies suggest it may help mild anxiety. However, kava has been linked to rare but serious liver damage, so it should be used with caution, avoided by people with liver problems, and only used after talking with your pharmacist or doctor.

Read the full Kava monograph & all interactions
Medication

About Phenytoin

What Is Phenytoin Used For?

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

Phenytoin treats seizures. Oral products are used for generalized tonic-clonic (grand mal) seizures and for psychomotor (temporal lobe) or complex partial seizures. Most oral products are also used to prevent and treat seizures during or after neurosurgery.

Phenytoin Sodium Injection is used for generalized tonic-clonic status epilepticus (a prolonged, dangerous seizure emergency). It is also used for seizures during neurosurgery. The injection should be used only when taking phenytoin by mouth is not possible. Dilantin-125 and Phenytoin oral suspension are listed for tonic-clonic and psychomotor seizures.

See full Phenytoin drug information
Keep checking

Other Drugs & Kava

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

247Major
581Moderate
338Minor
1,663No known interaction
247 Major 581 Moderate 338 Minor 1,663 No interaction
Major

247 interactions

Showing 60 of 247 major interactions — see all 247 on the Kava page.

Moderate

581 interactions

Showing 60 of 581 moderate interactions — see all 581 on the Kava page.

Minor

338 interactions

Showing 60 of 338 minor interactions — see all 338 on the Kava page.

No interaction 1,663 drugs checked — show the list

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

Showing the 60 most looked-up of 1,663 medications checked with no known interaction — see the full Kava list.

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

Can you take Kava with Phenytoin?
This is rated a major interaction, so the combination is best avoided unless your doctor or pharmacist has specifically told you otherwise. Read the full details on this page and confirm with your pharmacist before combining them.
Why are there 4 interactions listed for Kava and Phenytoin?
Phenytoin belongs to more than one drug category, and Kava 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 Kava and Phenytoin interaction?
We rate it Major. This is a clinically significant combination that is generally best avoided, or used only under the direct supervision of your physician or pharmacist.

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

Still Have a Question About Phenytoin and Kava?

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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.