Drug Interaction Report

Methsuximide and Evening Primrose: Interaction Details

Name: Methsuximide and Evening Primrose Interaction
Creator: Dr. Brian Staiger, PharmD, BCPS

A pharmacist-reviewed analysis of the Methsuximide and Evening Primrose interaction: the documented clinical effects, severity rating, onset, mechanism, and management considerations, with cited references throughout.

AI-assisted, pharmacist-reviewed · Source data updated Aug 8, 2026 · Sources: FDA labeling, DDInter 2.0, cited literature

Methsuximide

Celontin Celontin®

Evening Primrose

No brand names on record

Medically reviewed by

Dr. Brian Staiger, PharmD, BCPS

Updated Aug 8, 2026

Editorial policy · Data sources

Interaction severity

Moderate

Can be significant — usually manageable with monitoring.

Minor

Moderate

Major

Contraindicated

How we grade severity & evidence

Severity levels

Contraindicated: These should generally not be used together.
Major: Potentially serious — often needs a change or close monitoring.
Moderate: Can be significant — usually manageable with monitoring.
Minor: Usually limited clinical impact.

Evidence grades

Established: Well documented — supported by controlled studies or strong clinical data.
Probable: Good supporting evidence, though not definitively proven.
Suspected: Some evidence suggests this interaction, but it is not well established.
Possible: Limited or conflicting evidence; the interaction may occur.
Theoretical: Predicted from the drugs' pharmacology; not yet confirmed in people.

Ratings come from the documented interaction literature and are reviewed by a pharmacist. They describe the documented risk of the combination, not what will necessarily happen to you — your dose, timing, and health picture all matter.

Of 12 documented Methsuximide interactions, 6 are rated moderate — including this one.

Onset

delayed

Evidence

theoretical

Severity

Moderate

What happens

Reduced anticonvulsant effectiveness

Interaction Deep Dive

Evening primrose oil contains gamolenic acid (GLA), which may reduce the effectiveness of anticonvulsants by lowering the seizure threshold¹. Evening primrose oil is contraindicated in patients with epilepsy ²³.

Why it happens (mechanism)

Evening primrose oil may reduce the seizure threshold

Common questions

Can I take Methsuximide and Evening Primrose together?

Reduced anticonvulsant effectiveness Always confirm with your pharmacist or prescriber before making any change.

How serious is the Methsuximide and Evening Primrose interaction?

It is rated moderate. Can be significant — usually manageable with monitoring.

How quickly could this interaction happen?

The documented onset is "delayed". Effects tend to build up gradually over days to weeks.

How strong is the evidence for this interaction?

The evidence is graded "theoretical". Predicted from the drugs' pharmacology; not yet confirmed in people.

Questions for your pharmacist

Does my dose of Methsuximide or Evening Primrose need adjusting while I take them together?
What symptoms should prompt me to call you or my prescriber right away?
Does the timing of my doses matter for this combination?
Is there anything you'd monitor while I'm on both?

References (3)

Miller LG: Herbal medicinals: selected clinical considerations focusing on known or potential drug-herb interactions. Arch Intern Med 1998; 158:2200-2211.
Barber JH: Evening primrose oil:a panacea?. Pharm J 1988; 240:723-725.
Newall CA, Anderson LA, & Phillipson JDNewall CA, Anderson LA, & Phillipson JD: Herbal Medicines: A Guide for Health-Care Professionals, The Pharmaceutical Press, London, England, 1996.

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Methsuximide

Keep reading about Methsuximide

All Methsuximide interactions (12) Methsuximide drug information

Also serious with: Calcifediol Hydroxychloroquine Fosphenytoin Orlistat

Evening Primrose

Keep reading about Evening Primrose

All Evening Primrose interactions (23)

Beyond drug–drug

These medications also interact with supplements

Prescription drugs aren't the whole picture — herbal and dietary supplements can interact with them too. From the evidence-graded Natural Medicines database:

Methsuximide + 1,4-butanediol Activated Charcoal Beer Gamma-hydroxybutyrate (ghb) Kava L-tryptophan Wine 5-htp + 97 more

major · moderate · minor — check everything you take with our drug–supplement interaction checker.

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A message from HelloPharmacist

About our interaction database: depth, not breadth

HelloPharmacist doesn't license one of the big commercial interaction databases, so what you'll find here is not a complete list of every known drug interaction. Instead, each entry is researched, analyzed, and written up individually — documented from the published literature, reviewed by a pharmacist, and cited so you can check every source yourself.

If a combination isn't listed here, it means we haven't documented it yet — never that it's safe. For screening a full medication list, we recommend pairing this site with a comprehensive tool like the Drugs.com Interaction Checker and, most importantly, a review by your own pharmacist. For a deep, plain-English, fully sourced explanation of a specific documented interaction — that's exactly what we built this for.

This information is for education, not a substitute for professional medical advice. Do not start, stop, or change any medication without talking to your pharmacist or prescriber.