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Ethosuximide Side Effects

For the Consumer

Applies to ethosuximide: oral capsule liquid filled, oral syrup

In addition to its needed effects, some unwanted effects may be caused by ethosuximide. In the event that any of these side effects do occur, they may require medical attention.

Major Side Effects

You should check with your doctor immediately if any of these side effects occur when 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:
  • Attack, assault, or force
  • 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 and chills
  • fever with or without chills
  • general feeling of discomfort or illness
  • general feeling of tiredness or weakness
  • hair loss
  • headaches
  • high fever
  • hives, itching, and skin rash
  • joint or muscle pain
  • lower back or side pain
  • nervousness
  • not able to concentrate
  • painful or difficult urination
  • pale 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 with breathing
  • unexplained bleeding or bruising
  • 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

If any of the following symptoms of overdose occur while taking ethosuximide, get emergency help immediately:

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

Minor Side Effects

Some of the side effects that can occur with ethosuximide may not need medical attention. As your body adjusts to the medicine during treatment these side effects may go away. Your health care professional may also be able to tell you about ways to reduce or prevent some of these side effects. If any of the following side effects continue, are bothersome or if you have any questions about them, check with your health care professional:

  • 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


Gastrointestinal side effects have frequently included anorexia, vague gastric upset, nausea, vomiting, cramps, epigastric and abdominal pain, weight loss, and diarrhea. Gum hypertrophy and swelling of the tongue have also been reported.[Ref]


Hematologic side effects have included leukopenia, agranulocytosis, pancytopenia (with or without bone marrow suppression), and eosinophilia.[Ref]

Nervous system

Nervous system side effects have included drowsiness, headache, dizziness, euphoria, hiccups, irritability, hyperactivity, lethargy, fatigue, and ataxia.[Ref]


The manufacturer reports psychiatric side effects associated with ethosuximide therapy may be more frequent in patients who have previously exhibited psychosocial abnormalities.[Ref]

Psychiatric side effects have included sleep disturbances, night terrors, inability to concentrate, and aggressiveness. Paranoid psychosis, increased libido, and increased state of depression with overt suicidal intentions have been reported rarely.[Ref]


Dermatologic side effects have included urticaria, Stevens-Johnson syndrome (SJS), systemic lupus erythematosus, pruritic erythematous rashes, and hirsutism. SJS symptoms usually manifest within 28 days, but may occur later and can be fatal.[Ref]


Ocular side effects have included myopia.[Ref]


Genitourinary side effects have included vaginal bleeding and microscopic hematuria.[Ref]


Other side effects reported postmarketing have included Drug Reaction with Eosinophilia and Systemic Symptoms (DRESS).


1. "Product Information. Zarontin (ethosuximide)." Parke-Davis, Morris Plains, NJ.

Not all side effects for ethosuximide may be reported. You should always consult a doctor or healthcare professional for medical advice. Side effects can be reported to the FDA here.

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