Drug & supplement interaction

Glutamine + Fosphenytoin

Fosphenytoin brand name: Cerebyx.

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

Glutamine has a moderate interaction with Fosphenytoin. Theoretically, glutamine might antagonize the effects of anticonvulsant medications.

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

Glutamine and Fosphenytoin

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

Moderate

ANTICONVULSANTS

Why this applies to Fosphenytoin

Fosphenytoin falls under ANTICONVULSANTS — the group Glutamine interacts with.

Theoretically, glutamine might antagonize the effects of anticonvulsant medications.
Glutamine is metabolized to the excitatory neurotransmitter glutamate. Glutamate might have antagonistic effects with anticonvulsant drugs. However, this interaction 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 this pairing. Fosphenytoin is a seizure medicine that calms overactive electrical signals in the brain. Glutamine, once it's in your body, can be converted into glutamate, which is actually an excitatory brain chemical. So in theory, loading up on glutamine could nudge the brain in the opposite direction from what fosphenytoin is trying to do, possibly making seizure control a little less reliable.

I want to be honest with you though: this is a theoretical concern based on chemistry, not something that's been seen happening in real people. Because keeping seizures controlled matters so much, I wouldn't want you to start a glutamine supplement on your own. Run it by your doctor or pharmacist first, and let them know about any change in seizure frequency.

Contact Dr. Brian directly if you have additional questions on this interaction
References
  1. Meldrum BS. Glutamate as a neurotransmitter in the brain: review of physiology and pathology. J Nutr 2000;130:1007S-15S.. PubMed
  2. Garlick PJ. Assessment of the safety of glutamine and other amino acids. J Nutr 2001;131:2556S-61S.. PubMed
  3. Chapman AG. Glutamate and epilepsy. J Nutr 2000;130:1043S-5S.. 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

Glutamine Also Interacts With Other Medications

Glutamine has 49 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 49 No known interaction 2,781 (incl. Fosphenytoin)
Taking anything else?

Check Another of Your Medications Against Glutamine

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

From our Q&A

Questions About Glutamine or Fosphenytoin

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

This page covers Glutamine 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 Glutamine as Part of a Dietary Supplement Product? Check It for Interactions

We hold 5,253 real supplement products containing Glutamine, each one broken down to its full ingredient list — and combination products often carry several ingredients besides Glutamine. Your product may carry other ingredients that interact with Fosphenytoin too, on top of Glutamine — 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 Glutamine 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 Glutamine
Top 5%

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

29 days ago today
Medication Fosphenytoin
Steady interest

#2,051 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 Glutamine

What is Glutamine?

  • Muscle recovery and sports performance
  • Gut health and 'leaky gut'
  • Recovery from severe illness or injury
  • Immune support
  • Side effects of cancer treatment (mucositis)
  • Sickle cell disease (prescription form)

Glutamine is the most abundant amino acid in the body and is usually made in your muscles. A prescription form is FDA-approved to help reduce sickle cell disease complications, but for most popular uses such as muscle building, gut health, and immunity the evidence is limited or mixed. It is generally well tolerated in healthy people, but anyone with serious liver or kidney problems should check with a doctor first.

Read the full Glutamine 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 & Glutamine

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

0Major
49Moderate
0Minor
2,780No known interaction
49 Moderate 2,780 No interaction
Moderate

49 interactions

No interaction 2,780 drugs checked — show the list

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

Showing the 60 most looked-up of 2,780 medications checked with no known interaction — see the full Glutamine list.

See the full Glutamine 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
Glutamine 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 Glutamine and Fosphenytoin Together: Common Questions

Can you take Glutamine 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 Glutamine 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 Glutamine?

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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.