Drug & supplement interaction

Threonine + Ethosuximide

Ethosuximide brand name: Zarontin.

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

We found no known interaction between Threonine and Ethosuximide 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. Additionally, although there is no interaction, the two are separately associated with some of the same side effects, which would make a new symptom harder to attribute to one or the other.

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Interaction report

Threonine and Ethosuximide

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 Ethosuximide and Threonine 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.

Threonine safety at a glance

Threonine overall Use caution Threonine from food is safe; supplement safety at higher doses is not well studied.
Pregnancy Use caution Amounts from food are fine, but supplements have not been well studied in pregnancy, so avoid unless advised by a clinician.
Breastfeeding Use caution Dietary amounts are normal, but supplement use during breastfeeding has not been well studied.

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

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

Why No Interaction Is Listed for Ethosuximide

Interactions in our licensed database are recorded against drug classes, not just single drug names. Ethosuximide is filed under 7 classifications — including anticonvulsants, cytochrome p450 3a4 (cyp3a4) inducers, cns depressants. Threonine has documented interactions with 1 drug class — the most serious being nmda antagonists (major) — and none of Ethosuximide’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

Threonine Does Interact With Other Medications

Threonine has 3 major, known drug interactions in our database — Ethosuximide isn’t one of them. If you take anything else, check it against the full list below.

Major 3 No known interaction 2,827 (incl. Ethosuximide)
Taking anything else?

Check Another of Your Medications Against Threonine

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

What to actually watch for

No Interaction Found — But Data Suggests Threonine and Ethosuximide May Share Several of the Same Side Effects

This is not an interaction. Neither one changes how your body handles the other, and nothing here says they react together. What our sources do show is that each has separately been linked to the effects below — so taking both can make those effects more likely to turn up, and harder to pin on one or the other if they do.

  • Diarrhea Additional detail

    Threonine

    “Orally, some patients can experience minor gastrointestinal upset including diarrhea. Other side effects reported in people who have taken threonine include flatus and constipation.”

    Threonine · Natural Medicines adverse-effect record, reported in constipation.

    2 sources cited
    1. 12056. Lee A, Patterson V. A double blind study of L-threonine in patients with spinal spasticity. Acta Neurol Scand 1993;88:334-8. PubMed
    2. 681. Tandan R, Bromberg MB, Forshew D, et al. A controlled trial of amino acid therapy in amyotrophic lateral sclerosis: I. Clinical, functional, and maximum isometric torque data. Neurology 1996;47:1220-6. PubMed

    Ethosuximide

    Listed in the ADVERSE REACTIONS section of the FDA label for Ethosuximide. Read the label on DailyMed ›

  • Headache Additional detail

    Threonine

    “Orally, headache has been reported in people who have taken threonine.”

    Threonine · Natural Medicines adverse-effect record, reported in cluster headache.

    1 source cited
    1. 681. Tandan R, Bromberg MB, Forshew D, et al. A controlled trial of amino acid therapy in amyotrophic lateral sclerosis: I. Clinical, functional, and maximum isometric torque data. Neurology 1996;47:1220-6. PubMed

    Ethosuximide

    Listed in the ADVERSE REACTIONS section of the FDA label for Ethosuximide. Read the label on DailyMed ›

Reported for Threonine but not commonly for Ethosuximide: stomach upset and constipation.

Effects for Ethosuximide come from the ADVERSE REACTIONS section of its FDA label; effects for Threonine come from the Natural Medicines adverse-effect record, quoted above. Where a percentage is shown, it is the share of 2,490 voluntary FDA FAERS reports for Ethosuximide that mention that effect — a reporting proportion, not an incidence rate and not evidence the drug caused it. Wording is matched across sources by our own clinical vocabulary, so treat this as a prompt to pay attention, not a diagnosis.

Everything else you take

See Every Supplement That Interacts With Ethosuximide

This page covers Threonine only. If you take other supplements — a multivitamin, a sleep aid, something for joints — the Ethosuximide page lists 226 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 Grapefruit (major).

By severity: 9 major · 179 moderate · 38 minor.

From our pharmacist’s overview on the Ethosuximide page

“Ethosuximide (Zarontin) prevents absence seizures, and a steady blood level is what keeps them away, so I treat this list of 226 interacting supplements and herbs with real care, especially the nine rated major. More than half of the entries can change how the liver clears the drug; grapefruit can raise its level while St.”

Reviewed by 2 · Jul 18, 2026

Open the Ethosuximide interaction page

One more smart check

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

We hold 1,803 real supplement products containing Threonine, each one broken down to its full ingredient list — and combination products often carry several ingredients besides Threonine. Even though Threonine itself has no known interaction with Ethosuximide, 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 Threonine and Ethosuximide 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 Threonine
Top 25%

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

29 days ago today
Medication Ethosuximide
Steady interest

#2,341 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 Threonine reference on this page ↓
  • Freshness: we automatically re-check this combination every week — this pair was last verified September 20, 2026. The Threonine and Ethosuximide records this page draws on were last updated July 10, 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 Threonine

What is Threonine?

  • General amino acid/protein support
  • Muscle and tissue health
  • Immune support
  • Nervous system support (as a precursor)
  • Liver health (proposed)

Threonine is an essential amino acid your body needs but cannot make, so you must get it from food or supplements. Most people get plenty from a normal diet, and high-quality evidence for taking it as a separate supplement is limited. If you are considering threonine supplements, talk with your pharmacist or doctor first.

Amino acid (obtained from dietary protein or made synthetically) · Capsules, tablets, powder, and part of amino acid blends; also found in protein-rich foods

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

Threonine: dosing

There is no well-established standard supplement dose of threonine for general health. Studies that have used it for specific medical conditions used different amounts, and those doses were given under medical supervision.If you choose to use a threonine product, follow the directions on the label and do not exceed the recommended amount.

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

Read the full Threonine monograph & all interactions
Medication

About Ethosuximide

What Is Ethosuximide Used For?

Brand name: Zarontin

Ethosuximide — sold as Zarontin and also available as generic Ethosuximide — is used to control absence (petit mal) epilepsy. Absence seizures are brief episodes where a person loses awareness for a few seconds, often mistaken for daydreaming.

Both Zarontin and Ethosuximide products (capsule and oral solution forms) are approved for this use. Either may also be used alongside other seizure medicines when a patient has absence seizures together with other types of epilepsy.

Most-Reported Side Effects for Ethosuximide

From FAERS, the FDA’s public side-effect reporting system (2,490 reports, all brands). Reports are voluntary and are not proof the drug caused the effect.

Seizure 367 reports
Somnolence 157 reports
Generalised tonic-clonic seizure 149 reports
Petit mal epilepsy 118 reports
Treatment failure 116 reports
See full Ethosuximide drug information
Keep checking

Other Drugs & Threonine

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

3Major
0Moderate
0Minor
2,826No known interaction
3 Major 2,826 No interaction
Major

3 interactions

No interaction 2,826 drugs checked — show the list

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

Showing the 60 most looked-up of 2,826 medications checked with no known interaction — see the full Threonine list.

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

Threonine References

The 4 references that drive our Threonine 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. Tandan R, Bromberg MB, Forshew D, et al. A controlled trial of amino acid therapy in amyotrophic lateral sclerosis: I. Clinical, functional, and maximum isometric torque data. Neurology 1996;47:1220-6. PubMed
  2. Lee A, Patterson V. A double blind study of L-threonine in patients with spinal spasticity. Acta Neurol Scand 1993;88:334-8. PubMed
  3. Blin O, Pouget J, Aubrespy G, et al. A double-blind placebo controlled trial of L-threonine in amyotrophic lateral sclerosis. J Neurol 1992;239:79-81.
  4. Roufs JB. L-threonine as a symptomatic treatment for amyotrophic lateral sclerosis (ALS). Med Hypotheses 1991;34:20-3. PubMed

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 Threonine and Ethosuximide Together: Common Questions

Is it safe to take Threonine with Ethosuximide?
We do not list a known interaction between Threonine and Ethosuximide. 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.
Do Threonine and Ethosuximide have any of the same side effects?
Yes — our sources link each of them separately to 2 of the same effects. That is not an interaction: neither changes how your body handles the other. It does mean that if one of those effects turns up, it can be harder to tell which one is behind it. They are listed on this page with the source behind each.
How was the Threonine and Ethosuximide combination checked?
Interactions in our licensed database are recorded against drug classes. Ethosuximide is filed under 7 classifications, and Threonine has documented interactions with 1 drug class — none of Ethosuximide'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 Threonine interact with any other medications?
Yes. Threonine has 3 documented drug interactions in our database — Ethosuximide 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 Ethosuximide interact with any supplements?
Yes. Ethosuximide has documented interactions with 226 supplements in our database — Threonine is not one of them. The Ethosuximide 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

Threonine monograph Uses, safety profile, and every drug interaction in one place Ethosuximide drug information The full plain-English guide to this medication Ethosuximide supplement interactions Every supplement checked against Ethosuximide, 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 4 citations behind this page Ask a pharmacist Free, personal answer from our licensed team

Still Have a Question About Ethosuximide and Threonine?

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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.