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Zarontin Side Effects

Generic name: ethosuximide

Medically reviewed by Last updated on Aug 4, 2022.

Note: This document contains side effect information about ethosuximide. Some dosage forms listed on this page may not apply to the brand name Zarontin.

Applies to ethosuximide: oral capsule liquid filled, oral syrup.

Serious side effects of Zarontin

Along with its needed effects, ethosuximide (the active ingredient contained in Zarontin) may cause some unwanted effects. Although not all of these side effects may occur, if they do occur they may need medical attention.

Check with your doctor immediately if any of the following side effects occur while taking ethosuximide:


  • Changes in behavior
  • discouragement
  • feeling sad or empty
  • irritability
  • lack of appetite
  • loss of interest or pleasure
  • mood or mental changes
  • thoughts of killing oneself
  • tiredness
  • trouble with concentrating
  • trouble with sleeping

Incidence not known

  • Bleeding gums
  • blistering, peeling, or loosening of the skin
  • blood in the urine
  • bloody, black, or tarry stools
  • chest pain
  • cough or hoarseness
  • diarrhea
  • enlarged gums
  • false or unusual sense of well-being
  • fever with or without chills
  • general feeling of discomfort or illness
  • hair loss
  • headaches
  • high fever
  • hives, itching, skin rash
  • joint or muscle pain
  • lower back or side pain
  • nervousness
  • not able to concentrate
  • painful or difficult urination
  • pale skin
  • pinpoint red spots on the skin
  • red skin lesions, often with a purple center
  • red, irritated eyes
  • restlessness
  • shakiness and unsteady walk
  • sore throat
  • sores, ulcers, or white spots on the lips or in the mouth
  • swelling around the eyes
  • swelling of the tongue
  • swollen, painful, or tender lymph glands in the neck, armpit, or groin
  • trouble sitting still
  • trouble breathing
  • unsteadiness, trembling, or other problems with muscle control or coordination
  • unusual bleeding or bruising
  • unusual tiredness or weakness
  • vaginal bleeding
  • vision changes
  • yellow eyes or skin

Get emergency help immediately if any of the following symptoms of overdose occur while taking ethosuximide:

Symptoms of overdose

  • Change in consciousness
  • irregular, fast or slow, or shallow breathing
  • loss of consciousness
  • pale or blue lips, fingernails, or skin

Other side effects of Zarontin

Some side effects of ethosuximide may occur that usually do not need medical attention. These side effects may go away during treatment as your body adjusts to the medicine. Also, your health care professional may be able to tell you about ways to prevent or reduce some of these side effects.

Check with your health care professional if any of the following side effects continue or are bothersome or if you have any questions about them:


  • Increased in sexual ability, desire, drive, or performance
  • increased interest in sexual intercourse

Incidence not known

  • Cramps
  • dizziness
  • drowsiness
  • heartburn
  • hiccups
  • increased hair growth, especially on the face
  • loss of appetite
  • nausea or vomiting
  • nearsightedness
  • pain or discomfort in the chest, upper stomach, or throat
  • redness of the skin
  • unusual drowsiness, dullness, tiredness, weakness, or feeling of sluggishness
  • weight loss

For Healthcare Professionals

Applies to ethosuximide: oral capsule, oral syrup.


The more commonly reported adverse reactions have included gastrointestinal symptoms such as anorexia, vague gastric upset, nausea and vomiting, and abdominal pain.


Frequency not reported: Anorexia, vague gastric upset, nausea, vomiting, cramps, epigastric and abdominal pain, weight loss, gum hypertrophy, diarrhea, swollen tongue, hiccups[Ref]


Frequency not reported: Urticaria, Stevens-Johnson syndrome (SJS), pruritic erythematous rashes, hirsutism, Drug Reaction with Eosinophilia and Systemic Symptoms (DRESS), systemic lupus erythematosus[Ref]


Frequency not reported: Leukopenia, agranulocytosis, pancytopenia (with or without bone marrow suppression), eosinophilia, drug-induced immune thrombocytopenia[Ref]

Nervous system

Frequency not reported: Drowsiness, headache, dizziness, lethargy, fatigue, ataxia[Ref]


Rare (less than 0.1%): Paranoid psychosis, increased libido, increased state of depression with overt suicidal intentions

Frequency not reported: Disturbances, night terrors, inability to concentrate, aggressiveness, euphoria, irritability, hyperactivity[Ref]


Frequency not reported: Myopia[Ref]


Frequency not reported: Vaginal bleeding, microscopic hematuria[Ref]


Frequency not reported: Allergic reaction


1. "Product Information. Zarontin (ethosuximide)." Parke-Davis (2001):

Further information

Always consult your healthcare provider to ensure the information displayed on this page applies to your personal circumstances.

Some side effects may not be reported. You may report them to the FDA.