Drug & supplement interaction

Ketogenic Diet + Mephenytoin

Mephenytoin brand name: Mesantoin.

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

Ketogenic Diet has a moderate interaction with Mephenytoin. Following the ketogenic diet may reduce the levels of certain anticonvulsants, although the clinical significance of this effect is unclear.

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

Ketogenic Diet and Mephenytoin

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

Moderate

ANTICONVULSANTS

Why this applies to Mephenytoin

Mephenytoin falls under ANTICONVULSANTS — the group Ketogenic Diet interacts with.

Following the ketogenic diet may reduce the levels of certain anticonvulsants, although the clinical significance of this effect is unclear.
Pharmacokinetic research in patients chronically taking up to 4 antiepileptic drugs shows that following a modified Atkins diet for 4-12 weeks reduces the average anticonvulsant serum concentrations by 10.5% to 13.5% (range 7% to 19%) without affecting overall seizure control. Antiepileptic agents taken by these patients included carbamazepine, oxcarbazepine, topiramate, valproate, clobazam, nitrazepam, lamotrigine, zonisamide, and others. Levels of oxcarbazepine and levetiracetam did not seem to be significantly affected after the initiation of the ketogenic diet. Additionally, a small clinical study in children with drug-refractory epilepsy taking a variety of anticonvulsant medications shows that following a ketogenic diet for 12 weeks reduces serum concentrations of clobazam and its active metabolite desmethylclobazam, both by 38%, and lamotrigine by 15% without affecting overall seizure control. Levels of levetiracetam, topiramate, and valproic acid were not significantly reduced. Serum levels of anticonvulsants should be monitored in patients following a ketogenic diet.
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 practical takeaway if you take mephenytoin (Mesantoin) for seizures and you're thinking about a ketogenic or low-carb diet. The research we have suggests that going into ketosis can modestly lower the blood levels of many anticonvulsants, often somewhere around 10% to 15%. In the studies, that small dip usually didn't worsen seizure control, but it's something to keep an eye on.

For mephenytoin specifically, lower levels could theoretically mean a bit less seizure protection, so the concern is breakthrough seizures rather than extra side effects. Keep in mind this is based on weak, mostly anecdotal evidence, and mephenytoin itself wasn't directly studied. The safe move is simple: don't start a keto diet without telling your doctor or pharmacist first, since your blood levels may need to be checked and your dose adjusted if needed.

Contact Dr. Brian directly if you have additional questions on this interaction
References
  1. Kverneland M, Taubøll E, Selmer KK, Iversen PO, Nakken KO. Modified Atkins diet may reduce serum concentrations of antiepileptic drugs. Acta Neurol Scand. 2015;131(3):187-90. PubMed
  2. Kverneland M, Taubøll E, Molteberg E, Veierød MB, Selmer KK, Nakken KO, Iversen PO. Pharmacokinetic interaction between modified Atkins diet and antiepileptic drugs in adults with drug-resistant epilepsy. Epilepsia. 2019;60(11):2235-2244. PubMed
  3. Pedersen S, Kverneland M, Rudi K, et al. Decreased serum concentrations of antiseizure medications in children with drug resistant epilepsy following treatment with ketogenic diet. Epilepsia Open. 2023;8(3):858-866. 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

Ketogenic Diet Also Interacts With Other Medications

Ketogenic Diet has 136 moderate, 122 minor known drug interactions in our database — the Mephenytoin one above is one of them. If you take anything else, check it against the full list below.

Moderate 136 Minor 122 No known interaction 2,572 (incl. Mephenytoin)
Taking anything else?

Check Another of Your Medications Against Ketogenic Diet

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

Everything else you take

See Every Supplement That Interacts With Mephenytoin

This page covers Ketogenic Diet only. If you take other supplements — a multivitamin, a sleep aid, something for joints — the Mephenytoin page lists 215 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 · 178 moderate · 28 minor.

From our pharmacist’s overview on the Mephenytoin page

“Anyone taking mephenytoin (Mesantoin) for seizures should read this page with genuine care rather than as background noise. The biggest cluster of interactions piles sedation on top of a drug that already slows the nervous system, and alcohol, whether beer or wine, sits at the serious end of that group.”

Reviewed by 2 · Jul 18, 2026

Open the Mephenytoin interaction page

How much people look this up

Where Ketogenic Diet and Mephenytoin 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 Ketogenic Diet
Steady interest

#1,020 of 1,452 supplements looked up here in the last 7 days

29 days ago today
Medication Mephenytoin
Top half

#1,344 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.

Eating pattern

About Ketogenic Diet

What is Ketogenic Diet?

  • Weight loss
  • Type 2 diabetes and blood sugar control
  • Drug-resistant epilepsy (especially in children)
  • Reducing appetite
  • Athletic and metabolic interest

The ketogenic diet is a very low-carbohydrate, high-fat eating plan that shifts the body to burn fat for fuel. It has the strongest evidence as a medical therapy for hard-to-treat epilepsy and may help short-term weight loss and blood sugar, but it can be hard to sustain and is not right for everyone. Talk with a doctor or pharmacist before starting, especially if you have a medical condition or take medication.

Read the full Ketogenic Diet monograph & all interactions
Keep checking

Other Drugs & Ketogenic Diet

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

0Major
136Moderate
122Minor
2,571No known interaction
136 Moderate 122 Minor 2,571 No interaction
Moderate

136 interactions

Showing 60 of 136 moderate interactions — see all 136 on the Ketogenic Diet page.

Minor

122 interactions

Showing 60 of 122 minor interactions — see all 122 on the Ketogenic Diet page.

No interaction 2,571 drugs checked — show the list

We also checked Ketogenic Diet 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 Ketogenic Diet list.

See the full Ketogenic Diet interactions page
See every supplement checked against Mephenytoin, 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
Ketogenic Diet monograph › Uses, safety, and every drug interaction in one place Mephenytoin supplement interactions › Every supplement checked against Mephenytoin, 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

Following Ketogenic Diet While Taking Mephenytoin: Common Questions

Can you follow Ketogenic Diet while taking Mephenytoin?
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 Ketogenic Diet and Mephenytoin 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 Mephenytoin and Ketogenic Diet?

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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.