ethosuximide
Brand names: Zarontin
Ethosuximide is a medicine that helps control absence seizures. It belongs to a class of drugs called anticonvulsants.
Drug Pricing (NADAC)
Generic Price
$0.23/unit
Generic Available
Yes (6 manufacturers)
Pricing data from NADAC (CMS), effective December 18, 2024. Compare all drug costs →
What it does
Ethosuximide is used to control absence seizures, also known as petit mal epilepsy.
Common side effects
Loss of appetite, Upset stomach, Nausea
Key warnings
Ethosuximide can cause serious blood problems.
How It Works
Ethosuximide works by reducing unusual electrical activity in the brain. This helps to prevent absence seizures. The exact way it does this is not completely understood.
How to Take It
Take ethosuximide capsules by mouth. If you are 3 to 6 years old, you will usually start with one 250 mg capsule daily. If you are 6 years or older, you will usually start with two 250 mg capsules (500 mg total) daily. Your doctor may change your dose every 4 to 7 days to best control your seizures. Follow your doctor's instructions carefully.
Pregnancy & Breastfeeding
Tell your doctor if you are pregnant or plan to become pregnant. It is not known if ethosuximide will harm your unborn baby. Talk to your doctor about the risks and benefits of taking this medicine during pregnancy and breastfeeding.
Missed Dose
If you miss a dose, take it as soon as you remember. If it is almost time for your next dose, skip the missed dose and continue with your regular schedule.
Storage
Store ethosuximide capsules at room temperature, away from heat and moisture.
Side Effects (from patient reports)
Based on 1,914 FDA adverse event reports.
FDA Adverse Event Report Analysis
Detailed analysis of 2,415 reports from the FDA Adverse Event Reporting System (FAERS). Reports span 2004–2025.
Total Reports
2,415
Death-Related Reports
62
Hospitalization Reports
568
Top Indication
Epilepsy
Gender Distribution
Age Distribution
Most Reported Adverse Reactions (FAERS)
| # | Reaction | Reports |
|---|---|---|
| 1 | DRUG INEFFECTIVE | 498 |
| 2 | SEIZURE | 347 |
| 3 | OFF LABEL USE | 225 |
| 4 | SOMNOLENCE | 146 |
| 5 | GENERALISED TONIC-CLONIC SEIZURE | 140 |
| 6 | PETIT MAL EPILEPSY | 117 |
| 7 | TREATMENT FAILURE | 114 |
| 8 | DRUG INTERACTION | 113 |
| 9 | FATIGUE | 109 |
| 10 | EPILEPSY | 105 |
| 11 | MULTIPLE-DRUG RESISTANCE | 101 |
| 12 | CONDITION AGGRAVATED | 99 |
| 13 | VOMITING | 95 |
| 14 | STATUS EPILEPTICUS | 89 |
| 15 | DECREASED APPETITE | 81 |
Reactions in Death Reports
Reactions in Hospitalization Reports
Source: FDA FAERS (Adverse Event Reporting System) FDA FAERS (Adverse Event Reporting System) Reports are voluntary and do not establish causation
Serious Warnings
Ethosuximide can cause serious blood problems. Tell your doctor right away if you have a fever, sore throat, or unusual bleeding or bruising. Rarely, this medicine can cause severe allergic reactions or liver problems.
Known Drug Interactions
In addition, carbamazepine causes, or would be expected to cause, decreased levels of the following drugs, for which monitoring of concentrations or dosage adjustment may be necessary: acetaminophen, albendazole, alprazolam, aprepitant, buprenorphone, bupropion, citalopram, clonazepam, clozapine, corticosteroids (e.g., prednisolone, dexamethasone), cyclosporine, dicumarol, dihydropyridine calcium channel blockers (e.g., felodipine), doxycycline, ethosuximide, everolimus, haloperidol, imatinib, itraconazole, lamotrigine, levothyroxine, methadone, methsuximide, mianserin, midazolam, olanzapin...
Mechanism: Carbamazepine causes your body to process and remove ethosuximide faster than usual, leading to lower levels of the drug in your system.
What to do: Your doctor may need to monitor your blood levels or adjust your dose of ethosuximide.
Table 1: Drugs That Affect Phenytoin Concentrations Interacting Agent Examples Drugs that may increase phenytoin serum levels Antiepileptic drugs Ethosuximide, felbamate, oxcarbazepine, methsuximide, topiramate Azoles Fluconazole, ketoconazole, itraconazole, miconazole, voriconazole Antineoplastic agents Capecitabine, fluorouracil Antidepressants Fluoxetine, fluvoxamine, sertraline Gastric acid reducing agents H 2 antagonists (cimetidine), omeprazole Sulfonamides Sulfamethizole, sulfaphenazole, sulfadiazine, sulfamethoxazole trimethoprim Other Acute alcohol intake, amiodarone, chloramphenic...
Mechanism: Ethosuximide can slow down the breakdown of phenytoin in your body, which may lead to higher levels of phenytoin in your blood.
What to do: Your doctor may need to check your blood levels and lower your phenytoin dose to avoid side effects.
diazepam, ethosuximide, lamotrigine, phenytoin) by inhibiting their metabolism or protein binding displacement ( 7.2 ) • Patients stabilized on rufinamide should begin valproate therapy at a low dose, and titrate to clinically effective dose ( 7.2 ) • Dosage adjustment of amitriptyline/nortriptyline, propofol, warfarin, and zidovudine may be necessary if used concomitantly with valproate ( 7.2 ) • Topiramate: Hyperammonemia and encephalopathy ( 5.9 , 7.3 ) 7.1 Effects of Co-Administered Drugs on Valproate Clearance Drugs that affect the level of expression of hepatic enzymes, particularly t...
Mechanism: Valproate can slow down how your body breaks down ethosuximide or change how it travels in your blood. This can cause the level of ethosuximide in your body to rise.
What to do: Your doctor may need to adjust your ethosuximide dose and watch for any new side effects.
Common Questions
Can I take ethosuximide with other seizure medicines?
Will ethosuximide cure my epilepsy?
How long will I need to take ethosuximide?
Can ethosuximide affect my mood?
What should I do if I have side effects?
Can I drink alcohol while taking ethosuximide?
Does ethosuximide interact with other medicines?
Will ethosuximide affect my ability to drive?
How often will I see my doctor while taking ethosuximide?
What do the capsules look like?
What are the common side effects of ethosuximide?
Does ethosuximide interact with other medications?
What drug class is ethosuximide?
Is ethosuximide safe during pregnancy?
Related Medications in Anticonvulsant (Succinimide)
Other drugs grouped near ethosuximide — same-class peers and common alternatives.
brivaracetam
Briviact
Brivaracetam is a medicine used to treat partial-onset seizures.
Compare with ethosuximide →
cannabidiol
Epidiolex
Epidiolex is a medicine that contains cannabidiol.
Compare with ethosuximide →
carbamazepine
Tegretol
Carbamazepine is a medicine used to control seizures and treat nerve pain.
Compare with ethosuximide →
cenobamate
Xcopri
Xcopri is a medicine used to treat partial-onset seizures in adults.
Compare with ethosuximide →
clobazam
Onfi, Sympazan
Clobazam oral suspension is a medicine used with other medicines to treat seizures caused by Lennox-Gastaut syndrome.
Compare with ethosuximide →
Medication Guides
Understanding Drug Interactions
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Common Drug Interactions
Dangerous medication combinations and how to protect yourself
Related Health & Safety Data
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What the FDA Data Shows for ethosuximide
The FDA label for ethosuximide (sold under brand names such as Zarontin) classifies it as a prescription-only medication in the Anticonvulsant (Succinimide) class. Ethosuximide is used to control absence seizures, also known as petit mal epilepsy. Official labeling lists 18 commonly reported side effects, including Loss of appetite, Upset stomach, Nausea.
Post-market surveillance from the FDA Adverse Event Reporting System (FAERS) captures real-world experience. For this drug, FAERS contains 1,914 voluntary reports. The database also lists 3 documented drug interactions derived from FDA labeling, with the top-flagged interaction rated minor severity. NADAC pricing from CMS shows a generic unit cost of $0.23.
Report counts do not establish causation — a FAERS entry documents a temporal association, not proof that the drug produced the outcome. Widely prescribed medications naturally accumulate more reports than niche therapies, so raw totals must be interpreted alongside total exposure. Shortage status, recall history, and patent information further shape supply and switching decisions. This page summarizes public FDA data for educational purposes only and is not a substitute for professional medical advice — always consult a licensed healthcare provider before starting, stopping, or changing any medication.
Data Sources
Drug labeling: FDA Drug Labels (SPL/DailyMed). Adverse events: FDA Adverse Event Reporting System (FAERS). Pricing: CMS National Average Drug Acquisition Cost (NADAC).
FAERS reports are voluntary and do not establish causation. Drug interactions are derived from FDA labeling and clinical references. Always consult a healthcare professional before making medication decisions.
Last updated: December 23, 2021
Read our methodology — how this data is sourced, computed, and verified.
All federal data sources used on this page
- FDA Orange Book — approved drug products with therapeutic equivalence. accessdata.fda.gov/cder/ob
- FDA DailyMed — NIH-hosted drug labeling for FDA-approved meds. dailymed.nlm.nih.gov
- FDA Adverse Event Reporting System (FAERS) — post-marketing safety surveillance. fda.gov/drugs/faers
- NLM RxNorm — standardized clinical drug nomenclature. nlm.nih.gov/research/umls/rxnorm
- CMS Medicare Part B Drug Average Sales Price Files — federal drug pricing data. cms.gov/medicare/part-b-drugs/asp
- FDA Drug Shortages Database — current and resolved drug shortage tracking. accessdata.fda.gov/drugshortages