Ethosuximide: uses, dosing, side effects & brands
Ethosuximide is a medicine sold in the U.S. under 2 brand and generic names, for absence epilepsy. Below: what the FDA label says, every product that contains it, what the pills look like, and its recall record.
Key facts
- Treats (across its forms)
- Absence Epilepsy
- Available as
- Capsule · Solution
- Sold as
- 2 products — Ethosuximide and Zarontin
- Prescription?
- Prescription only
- Generic available?
- Yes
- What the pharmacy pays
- about $7 for a 30-count supply — not your price
How ethosuximide is dosed
From the FDA label for Zarontin (application NDA012380). Other ethosuximide products — different forms, different strengths — are dosed differently. Follow the label for the one you were prescribed.
Zarontin is administered by the oral route. The initial dose for patients 3 to 6 years of age is one capsule (250 mg) per day; for patients 6 years of age and older, 2 capsules (500 mg) per day. The dose thereafter must be individualized according to the patient's response. Dosage should be increased by small increments. One useful method is to increase the daily dose by 250 mg every four to seven days until control is achieved with minimal side effects. Dosages exceeding 1.5 g daily, in divided doses, should be administered only under the strictest supervision of the physician. The optimal dose for most pediatric patients is 20 mg/kg/day. This dose has given average plasma levels within the accepted therapeutic range of 40 to 100 mcg/mL. Subsequent dose schedules can be based on effectiveness and plasma level determinations. Zarontin may be administered in combination with other anticonvulsants when other forms of epilepsy coexist with absence (petit mal). The optimal dose for most pediatric patients is 20 mg/kg/day.
Ethosuximide side effects
Body As A Whole: Allergic reaction, Drug Reaction with Eosinophilia and Systemic Symptoms (DRESS). Gastrointestinal System: Gastrointestinal symptoms occur frequently and include anorexia, vague gastric upset, nausea and vomiting, cramps, epigastric and abdominal pain, weight loss, and diarrhea. There have been reports of gum hypertrophy and swelling of the tongue. Hemopoietic System: Hemopoietic complications associated with the administration of ethosuximide have included leukopenia, agranulocytosis, pancytopenia, with or without bone marrow suppression, eosinophilia, and thrombocytopenia (see WARNINGS ). Nervous System: Neurologic and sensory reactions reported during therapy with ethosuximide have included drowsiness, headache, dizziness, euphoria, hiccups, irritability, hyperactivity, lethargy, fatigue, and ataxia. Psychiatric or psychological aberrations associated with ethosuximide administration have included disturbances of sleep, night terrors, inability to concentrate, and aggressiveness. These effects may be noted particularly in patients who have previously exhibited psychological abnormalities. There have been rare reports of paranoid psychosis, increased libido, and increased state of depression with overt suicidal intentions. Integumentary System: Dermatologic manifestations which have occurred with the administration of ethosuximide have included urticaria,…
Who shouldn’t take ethosuximide
Ethosuximide should not be used in patients with a history of hypersensitivity to succinimides.
Ethosuximide drug interactions
Since Zarontin (ethosuximide) may interact with concurrently administered antiepileptic drugs, periodic serum level determinations of these drugs may be necessary (e.g., ethosuximide may elevate phenytoin serum levels and valproic acid has been reported to both increase and decrease ethosuximide levels).
Every ethosuximide product we track (2)
Same active ingredient — different manufacturer, form, price and FDA recall record. That last one is what our independent score measures.
| # | Drug | Rating | Type | Form | Generic? | Pharmacy pays | |
|---|---|---|---|---|---|---|---|
| 1 | 56/100 | Prescription | Capsule | Generic | $7 | View → | |
| 2 | Not yet rated | Prescription | Capsule | Generic | $7 | View → |
What ethosuximide pills look like
Imprint codes, colour and shape from the FDA’s labelling data. Match the imprint on your pill — or search any imprint.
How long ethosuximide keeps
No ethosuximide label we read sets a separate limit for after opening, but they do specify how it must be stored — and the stability behind any date assumes those conditions.
Does ethosuximide expire? The in-use limits and storage rules from its labelsEthosuximide and breastfeeding
From LactMed, the US National Library of Medicine’s Drugs and Lactation Database — quoted, not rewritten.
Full LactMed record for ethosuximide: levels in milk, effects in breastfed infants, and the drugs it would consider insteadAverage ethosuximide dosages of 50 to 60% of the maternal weight-adjusted dosage are excreted in human milk and infant plasma levels of 25 to 30% of maternal levels are common. Although no adverse effects attributable solely to ethosuximide in breastmilk have been reported, monitor the infant for drowsiness, adequate weight gain, and developmental milestones, especially in younger, exclusively breastfed infants and when using combinations of anticonvulsants. Measurement of an infant serum level might help rule out toxicity if there is a concern.
National Institute of Child Health and Human Development, record revised August 15, 2024. LactMed states its information is not a substitute for professional judgement.
What people report to the FDA about ethosuximide
The FDA Adverse Event Reporting System (FAERS) collects reports from patients and clinicians. It holds 1,897 reports naming ethosuximide, and the FDA flagged 84% of those reports as serious. The effects reported most often — leaving out reports about overdose, misuse or the condition being treated, which dominate the raw list for common medicines:
- seizure261 reports
- generalised tonic-clonic seizure128 reports
- somnolence122 reports
- treatment failure114 reports
- multiple-drug resistance104 reports
- status epilepticus95 reports
- petit mal epilepsy94 reports
- fatigue87 reports
Read these as a signal, not a rate. A report does not mean ethosuximide caused the effect — anyone can file one, and many describe people taking several medicines for several conditions. Crucially there is no denominator: FAERS does not record how many people took the drug, so these counts cannot be turned into “X% of patients” — a bigger number often just means a more widely used or more talked-about drug. Duplicates exist, and publicity drives reporting. For what is actually established, read the FDA label section above.
Source: openFDA drug/event (FAERS), retrieved August 25, 2026.
Related calculators
Frequently asked questions
What is ethosuximide?
Zarontin (Ethosuximide) is a medication used to treat Absence Epilepsy.
Can you take ethosuximide with other medicines?
It depends on the medicine. We check it against the FDA labels rather than guessing: our interaction checker searches each drug's own label for the other and quotes what it says, naming the section it came from. Run ethosuximide against whatever else you take — and remember that a label not naming a drug is not the same as that combination being safe.
What brand names is ethosuximide sold under?
We track 2 ethosuximide-containing products in the U.S.: Ethosuximide and Zarontin. They are the same active ingredient; they differ in form, manufacturer, price and FDA recall record.
What forms does ethosuximide come in?
Across the brands we track, ethosuximide is currently marketed as capsule and solution, per the FDA's National Drug Code Directory. Each form is dosed differently — follow the label for the exact product you were prescribed.
Is there a generic ethosuximide?
Yes. Our catalog lists 1 generic ethosuximide product alongside the brand versions. A generic has the same active ingredient and must meet the FDA's bioequivalence standard; it usually costs less. Ask your pharmacist which one your plan covers.
Cite this page
- APA
- pharmaranks. (2026, July 24). Ethosuximide: uses, dosing, side effects & brands. https://pharmaranks.com/drugs/ethosuximide
- MLA
- “Ethosuximide: uses, dosing, side effects & brands.” pharmaranks, 24 July 2026, https://pharmaranks.com/drugs/ethosuximide.
We summarise public FDA and NIH sources — for a clinical claim, cite the primary source we link to as well.
Sources: FDA openFDA drug label, National Drug Code Directory, and Enforcement (recall) database. This page reproduces public FDA data and is not medical advice. Dosing is set by your prescriber.
Read the full FDA label for ethosuximide on DailyMed (NIH) ↗.