Zarontin (Ethosuximide) - Oral

What Is Zarontin?

Zarontin (ethosuximide) is a prescription anti-epileptic drug (AED) approved for preventing absence seizures in adults and children aged 3 years and older. It is available in capsule form and as a syrup. 

This medication reduces absence seizures, suppressing the electroencephalogram (EEG) pattern associated with this type of seizure. Zarontin affects the calcium channels in the brain, which may play a role in its seizure prevention abilities.

Drug Facts

Generic Name: Ethosuximide

Brand Name(s): Zarontin

Administration Route: Oral

Drug Availability: Prescription

Therapeutic Classification: Anticonvulsant

Available Generically: Yes

Controlled Substance: N/A

Active Ingredient: Ethosuximide

Dosage Form(s): Syrup, capsule

What Is Zarontin Used For?

Zarontin is used on a daily basis to reduce the frequency of absence seizures. 

Absence seizures, sometimes also referred to as petit mal seizures, can occur when a person has an epilepsy disorder that involves several types of seizures, or it can be the only seizure type a person experiences (absence epilepsy).

The following can indicate a person is having an absence seizure:

  • A person will be unresponsive and unconscious.
  • Someone having an absence seizure appears as if they are staring, daydreaming, or deep in thought.
  • This seizure type doesn’t cause any abnormal physical movements during the episode.
  • After an absence seizure, a person will not recall the episode and will usually be able to continue with their activities without any limitations. 

Absence seizures generally occur during childhood and typically resolve as a child gets older. However, they can continue throughout adulthood for some people. Less often, they can begin during adulthood. 

Zarontin (Ethosuximide) Drug Information - Illustration by Zoe Hansen

Verywell / Zoe Hansen

How to Take Zarontin 

You should take this medication every day as directed by your healthcare provider.

You can take Zarontin with or without food. Make sure you measure the oral solution (syrup) with the measuring device provided to you. Take it at the same time every day and take it in a consistent way—for example, if you take it with food, you should always take it that way. Do not skip doses or stop taking Zarontin suddenly, as doing so can trigger a seizure.


Store Zarontin in its original container away from light and out of the reach of children and pets. Do not store it in the bathroom.

Keep Zarontin capsules at a temperature between 59 degrees to 86 degrees Fahrenheit (F). Zarontin oral solution syrup should be stored at 68 degrees to 77 degrees F. Do not freeze.

Off-Label Uses

This medication has been prescribed off-label for treating several conditions. The dosing for off-label indications is not well established. 

Off-label uses of Zaronitin include: 

You may experience side effects when taking Zarontin off-label. Be sure to familiarize yourself with potential side effects and talk to your healthcare provider if you experience any.

What Are the Side Effects of Zarontin?

Zarontin can cause side effects that can range from mild to serious. 

This is not a complete list of side effects and others may occur. A healthcare provider can advise you on side effects. If you experience other effects, contact your pharmacist or a healthcare provider. You may report side effects to the FDA at or 1-800-FDA-1088.

Common Side Effects

The most common side effects caused by Zarontin are:

  • Loss of appetite 
  • Drowsiness 
  • Headaches 
  • Nausea or vomiting
  • Indigestion, stomach discomfort 
  • Diarrhea
  • Weight loss
  • Loss of concentration
  • Hiccups
  • Tiredness 
  • Dizziness or lightheadedness
  • Unsteadiness when walking or balance problems 
  • Irritability 
  • Hyperactivity 
  • Bad dreams 
  • Excess hair growth 

Often, the common side effects are mild or temporary. But they can be intolerable or affect your quality of life. Tell your healthcare provider if any of these are persistent or if they bother you. You might need treatment for the side effects or a change in your Zarontin prescription. 

Severe Side Effects

Rarely, serious side effects can occur due to taking Zarontin. The serious side effects can be harmful to your health or even life-threatening. Get prompt medical attention if you begin to have signs or symptoms of these adverse reactions.

Severe side effects of Zarontin include:

  • Blood problems: Bruising, bleeding, fatigue, fever, swollen glands, frequent infections or an infection that does not go away. 
  • Inflammatory reaction: Joint pain, joint swelling
  • Muscle aches
  • Fever
  • Chest pain
  • Breathing problems
  • Swollen lymph nodes
  • Kidney damage 
  • Systemic lupus erythematosus (SLE)
  • Liver damage: Yellowish discoloration of the skin and eyes, abdominal discomfort, nausea, and vomiting 
  • Suicidal thoughts 
  • Hallucinations or delusions 
  • Stevens-Johnson syndrome
  • Serious allergic reactions: Rash, hives, mouth sores, peeling skin
  • Mouth and throat swelling
  • Seizures can be exacerbated 

These issues can cause serious health complications, or they could be life-threatening. You may need urgent medical treatment if you develop these symptoms, possibly with a long-term adjustment of your prescriptions. 

Long-Term Side Effects

The effects of Zarontin are expected to wear off within a few days after you stop taking it.

Many of the serious side effects of Zarontin can cause lasting effects. For example, liver or kidney damage may be irreversible. 

Pregnant people can have an increased risk of birth defects when taking Zarontin. However, the risk of seizures is dangerous during pregnancy as well. Discuss the potential benefits versus risks of taking Zarontin and other AEDs with your healthcare provider, ideally before you plan to become pregnant.

Report Side Effects

Zarontin may cause other side effects. Call your healthcare provider if you have any unusual problems while taking this medication.

If you experience a serious side effect, you or your healthcare provider may send a report to the FDA's MedWatch Adverse Event Reporting Program or by phone (800-332-1088).

Dosage: How Much Zarontin Should I Take?

Drug Content Provided and Reviewed by IBM Micromedex®

The dose of this medicine will be different for different patients. Follow your doctor's orders or the directions on the label. The following information includes only the average doses of this medicine. If your dose is different, do not change it unless your doctor tells you to do so.

The amount of medicine that you take depends on the strength of the medicine. Also, the number of doses you take each day, the time allowed between doses, and the length of time you take the medicine depend on the medical problem for which you are using the medicine.

  • For oral dosage form (capsules):
    • For seizures:
      • Adults and children 6 years of age and older—Dose is based on body weight and must be determined by your doctor. The starting dose is usually 500 milligrams (mg) once a day. Your doctor may increase your dose as needed.
      • Children 3 to 6 years of age—Dose is based on body weight and must be determined by your doctor. The starting dose is usually 250 mg once a day. Your doctor may increase your dose as needed.
      • Children younger than 3 years of age—Use and dose must be determined by your doctor.


There are cases in which your healthcare provider may modify your dosage or monitor you more closely while you are taking Zarontin.

Pregnancy and Breastfeeding

Studies suggest a link between AED use during pregnancy and an increased risk of birth defects. However, uncontrolled epilepsy can also be dangerous for people who are pregnant. If you are pregnant or plan to become pregnant, talk to your healthcare provider about your options. They will weigh the benefits and risks of using epileptic medication during your pregnancy.

Zarontin can pass through human breast milk, so nursing infants may be exposed to this medication. Talk to your healthcare provider if you plan to breastfeed. 

Liver of Kidney Problems

Zarontin should be used with caution in people with liver or kidney disease.

Missed Dose

Do not skip doses, even if you don’t have any seizures. If you accidentally miss a dose of your medication, take the missed dose once you remember it. However, skip the missed dose if it is almost time for your next scheduled dose and resume your normal dosing schedule.

Overdose: What Happens If I Take Too Much Zarontin?

Taking too much Zarontin can increase the likelihood of experiencing worsening side effects of the medication. 

Symptoms of an overdose can include:

  • Nausea 
  • Vomiting
  • Decreased alertness 
  • Coma 
  • Impaired breathing 

You may need symptomatic treatment for these effects. In some cases, medically induced vomiting, gastric lavage, activated charcoal, or hemodialysis may be necessary to reduce the amount of Zarontin in the body.

What Happens If I Overdose on Zarontin?

If you think you or someone else may have overdosed on Zarontin, call a healthcare provider or the Poison Control Center (800-222-1222).

If someone collapses, has a seizure, has trouble breathing, or can’t wake up after taking too much Zarontin, call 911 immediately.


Drug Content Provided and Reviewed by IBM Micromedex®

It is very important that your doctor check your progress closely while you or your child are using this medicine to see if it is working properly and to allow for a change in the dose. Blood and urine tests may be needed to check for any unwanted effects.

Do not stop taking this medicine without first checking with your doctor. Stopping the medicine suddenly may cause your seizures to return or to occur more often. Your doctor may want you or your child to gradually reduce the amount you are using before stopping completely.

This medicine may increase the chance of experiencing grand mal seizures in certain patients. Talk with your doctor if you have concerns about this risk.

Ethosuximide may cause some people to be agitated, irritable, or display other abnormal behaviors. It may also cause some people to have suicidal thoughts and tendencies or to become more depressed. If you, your child, or your caregiver notice any of these side effects, tell your doctor or your child's doctor right away.

This medicine may increase your risk of having systemic lupus erythematosus (SLE). Tell your doctor right away if you or your child has chest pain, fever and chills, general feeling of discomfort or illness, hair loss, headache, muscle or joint pain, skin rash, sore throat, swollen glands, or trouble breathing.

This medicine will lower the number of some types of blood cells in your body. Because of this, you may bleed or get infections more easily. To help with these problems, avoid being near people who are sick or have infections. Wash your hands often. Stay away from rough sports or other situations where you could be bruised, cut, or injured. Brush and floss your teeth gently. Be careful when using sharp objects, including razors and fingernail clippers.

Tell your doctor right away if you or your child feels unusually weak, starts bruising easily, has bleeding gums or nosebleeds, seems to be sick more often, has a fever, swollen glands, or a sore throat that will not go away.

Call your doctor right away if you or your child start to have persistent cough, weight loss, night sweats, fever, chills, or flu-like symptoms such as runny or stuffy nose, headache, blurred vision, or feeling generally ill.

Serious skin reactions, including Stevens-Johnson syndrome and drug reactions with eosinophilia and systemic symptoms (DRESS) can occur with this medicine, which can be life-threatening. Check with your doctor right away if you have black, tarry stools, blistering, peeling, or loosening of the skin, chest pain, chills, cough, diarrhea, itching, joint or muscle pain, painful or difficult urination, red irritated eyes, red skin lesions, often with a purple center, sore throat, sores, ulcers, or white spots in the mouth or on the lips, swollen glands, unusual bleeding or bruising, or unusual tiredness or weakness while you or your child are using this medicine.

Ethosuximide may cause dizziness, drowsiness, or less alert than they are normally. Make sure you know how you react to this medicine before you drive, use machines, or do anything else that could be dangerous if you are dizzy or are not alert.

Do not take other medicines unless they have been discussed with your doctor. This includes prescription or nonprescription (over-the-counter [OTC]) medicines and herbal or vitamin supplements.

What Are Reasons I Shouldn’t Take Zarontin? 

You should not take Zarontin if you are allergic to succinimides (methsuximide or ethosuximide) or any other ingredients in this medication.

There may be other reasons your healthcare provider may choose not to prescribe this medication for you, including:

  • Liver disease
  • Kidney disease
  • Lupus
  • History of depression, mood problems, or suicidal thoughts or behavior
  • Pregnancy 

Talk to your healthcare provider about your medical history before starting Zarontin. 

What Other Medications Interact With Zarontin?

Zarontin is sometimes prescribed with one or more AEDs for seizure control, especially when a person has other seizure types in addition to absence seizures. 

Zarontin can interact with other AEDs, including:

  • Phenytoin 
  • Valproic acid 

Your healthcare provider may periodically check the blood levels of these medications and may make adjustments based on blood levels or symptoms. 

What Medications Are Similar?

Zarontin is an AED. There are over 20 AEDs used for seizure prevention, and they are each effective for some, but not all, seizure types. 

Other AEDs used to prevent absence seizures include:

  • Valproic acid 
  • Lamotrigine 

Frequently Asked Questions

  • What Is Zarontin used for?

    Zarontin is used to prevent absence seizures, which are seizures characterized by a lack of awareness. These seizures do not cause involuntary movements.

  • How does Zarontin work?

    Zarontin alters electrical nerve activity in the brain and affects the action of calcium channels, which control nerve activity.

  • What drugs should not be taken with Zarontin?

    This medication interacts with other anti-seizure drugs, but they can generally be taken together.

  • How long does it take for Zarontin to work?

    This medication can start taking effect within a few hours, but it is not expected to prevent seizures therapeutically until after several days of use.

  • What are the side effects of Zarontin?

    The most common side effects are loss of appetite, dizziness, headaches, and drowsiness. Severe side effects can include liver failure, kidney failure, or severe skin reactions.

  • How do I stop taking Zarontin?

    You should not abruptly stop taking Zarontin. Suddenly discontinuing anti-seizure medication can cause a seizure. If you need to stop taking it, make sure you do so gradually, based on a schedule provided to you by your healthcare provider.

How Can I Stay Healthy While Taking Zarontin?

When taking Zarontin, pay special attention to factors affecting your condition and treatment regimen:

  • Avoid seizure triggers, including lack of sleep, alcohol, or skipping meals. Ask your healthcare provider what you should if you develop a fever, as fevers can trigger seizures. 
  • Do not drive, climb, swim, or operate machinery if you experience any drowsiness or diminished concentration.
  • Take the medication and all other medications as directed. Do not skip doses, even if you don’t have any seizures. 
  • Talk to your healthcare provider about potential side effects. Learn the warning signs of any serious reactions.

Medical Disclaimer

Verywell Health's drug information is meant for educational purposes only and not intended as a replacement for medical advice, diagnosis, or treatment from a healthcare provider. Consult your healthcare provider before taking any new medication(s). IBM Watson Micromedex provides some of the drug content, as indicated on the page.

8 Sources
Verywell Health uses only high-quality sources, including peer-reviewed studies, to support the facts within our articles. Read our editorial process to learn more about how we fact-check and keep our content accurate, reliable, and trustworthy.
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By Heidi Moawad, MD
Heidi Moawad is a neurologist and expert in the field of brain health and neurological disorders. Dr. Moawad regularly writes and edits health and career content for medical books and publications.