Side effects of zonisamide



Zonisamide is the generic form of the brand-name drug Zonegran, used with other medications to treat certain types of seizures in people with epilepsy.

This medicine has also been studied for its potential to help treat migraines, Parkinson’s disease and other movement disorders, bipolar disorder, and obesity.

Zonisamide is an anticonvulsant. It works by reducing abnormal electrical activity in the brain.

The Food and Drug Administration (FDA) approved zonisamide in 2000. It’s manufactured as Zonegran in the United States by Concordia Healthcare Corp.

Zonisamide Warnings

Before taking zonisamide, tell your doctor if you have, or have ever had:

  • Liver disease
  • Kidney problems or kidney stones
  • Lung or breathing difficulties
  • High blood acid levels
  • A mental illness, such as depression
  • A history of status epilepticus (long periods of continuous seizures, or a series of seizures without a return to consciousness)
  • Allergies to medications

Also, let your doctor know if you’re on a high-fat, low-carbohydrate diet (ketogenic diet) to control your seizures.

Zonisamide can make it harder for your body to cool down when it gets hot. Avoid exposure to extreme heat, and tell your doctor immediately if you have a fever or aren’t sweating as you usually do.

Let your healthcare provider know if you have diarrhea any time before or during your treatment.

Your mental health may change in unexpected ways while taking zonisamide. In clinical studies, a small number of people who took anticonvulsants such as zonisamide became suicidal.

Tell your doctor right away if you experience any of the following symptoms:

  • New or worsening depression, anxiety, or irritability
  • Violent, aggressive, or angry behavior
  • Thoughts of harming yourself
  • Agitation or restlessness
  • Panic attacks
  • Difficulty falling asleep or staying asleep
  • An abnormally excited mood
  • Withdrawal from family and friends
  • A preoccupation with death
  • Any other changes in behavior or mood

Your doctor will probably tell you to drink six to eight glasses of water every day while taking zonisamide. Follow these instructions carefully.

Some people who take medicines like zonisamide develop a severe, and sometimes fatal, reaction. Tell your doctor right away if you experience:

  • Fever, chills, cough, or sore throat
  • Rash
  • Swollen, blistered, or peeling skin
  • Red or irritated eyes
  • Sores in the mouth, throat, nose, or eyes
  • Unusual bleeding or bruising
  • Extreme fatigue
  • Pale skin
  • Severe stomach pain
  • Loss of appetite
  • Dark-colored urine or pale-colored stools

Be sure to tell your healthcare provider you’re taking this medicine before having any type of surgery, including a dental procedure.

Zonisamide may cause a condition called metabolic acidosis (high blood acid levels). Talk to your doctor about this risk.

This medicine shouldn’t be taken by children younger than 16. Children may be at higher risk for side effects such as kidney stones, heatstroke, reduced growth, and metabolic acidosis.

Continue to take zonisamide even if you feel well. Don’t stop taking this drug without first talking to your doctor.

If you stop taking this medicine suddenly, your seizures may worsen. Your doctor will probably tell you to stop taking zonisamide gradually if the drug is no longer helpful or needed.

Your doctor will want to order frequent tests to check your body’s response to zonisamide. Keep all appointments with your doctor’s office and laboratory.

Pregnancy and Zonisamide

Zonisamide can harm a fetus, so don’t take it if you’re pregnant. Contact your doctor right away if you become pregnant while taking this medicine.

Use an effective form of birth control while taking zonisamide.

Zonisamide passes into breast milk. Don’t breastfeed while taking this medicine.

Very few people have serious reactions to Zonegran. If you take it, you should be aware of them, however, so you and your family can recognize them. Here’s a list of warning signs that may be the start of one of these problems:

If you notice any of these symptoms, call your doctor right away:

  • Rash
  • Fever, sore throat, sores in your mouth, or easy bruising (could mean a blood problem)
  • Sudden back pain, pain in the stomach area, pain when urinating, or bloody or dark urine (could mean a kidney stone)
  • Decreased sweating or rise in body temperature, especially for a child
  • Depression
  • Thoughts that are unusual for you

If you notice mood changes with Zonegran, speak to your doctor or nurse. A slight reduction in the dosage may improve your frame of mind. If you had a history of depression before starting Zonegran, your doctor may consider other treatments such as antidepressants or referral to a counselor or psychiatrist.

The rash may take various forms, from small red spots or blotches on the surface of the skin to large blisters. It may be preceded or accompanied by itchiness. When you first start taking Zonegran (specifically during the first 2 to 4 weeks), watch closely for any signs of a rash. Alert your doctor if you detect changes in your skin. If a rash progresses, you may develop a fever or a feeling of sickness. Occasionally, fever comes before the rash.

Blood disorders
A few people have developed blood disorders called aplastic anemia and agranulocytosis while taking zonisamide. The numbers are so small that not much can be said about a possible relationship, but you should tell the doctor if you develop symptoms such as fever, sores in your mouth, or easy bruising.

Kidney stones
Kidney stones occurred in about 1 in 80 people, usually after taking Zonegran for 6 to 12 months. Most people who get kidney stones have had kidney stones before. Contact your doctor immediately if you develop symptoms that could indicate a kidney stone, such as sudden back pain, abdominal pain, or blood in the urine. Drinking more fluids may reduce the risk of stone formation. This is especially important if you or someone in your family has had kidney stones, because your risk is greater.

Decreased sweating
An effect reported only in children is decreased sweating leading to high body temperature, even heatstroke. This effect is quite rare, but parents of children or teenagers taking Zonegran should be watchful, especially in summer.

Depression or psychosis
Tell your doctor if you feel depressed or have thoughts that are unusual for you while you’re taking Zonegran. This is unusual but can happen.

A complete list of all reactions to Zonegran can be found in the package insert, but it is important to remember that only a tiny number of people have any of these serious problems.

On 2/23/2009, the US Food and Drug Administration issued a warning that the antiepileptic medication zonisamide (Zonegran) can cause metabolic acidosis in some patients. Metabolic acidosis is a condition of excess acidity (low pH) in the blood. The condition can manifest with a variety of symptoms, including chest pains, heart racing, rapid breathing, stomach upset, kidney stones, confusion and other symptoms. People who are already prone to have metabolic acidosis from kidney disease or drugs such as acetazolamide (Diamox), certain diabetes drugs or the ketogenic diet may be more prone to develop zonisamide-induced metabolic acidosis. Young people are also more likely to develop the condition. Metabolic acidosis is detected by measuring blood levels of bicarbonate (worrisome if less than 17 mEq/L), sometimes along with arterial blood gas measurement for levels of oxygen, carbon dioxide and acidity. Once diagnosed, the condition usually is treatable, most directly by stopping zonisamide. The FDA recommended that healthcare professionals measure serum bicarbonate before starting treatment and regularly thereafter.

On July 10, 2008, an advisory panel was convened by the Food and Drug Administration (FDA) to review data that the FDA had previously collected from drug studies showing an association between many of the antiepileptic drugs (AEDs) and suicidal ideation and behavior, which together are called suicidality. According to the FDA’s Alert, among the patients with epilepsy in these drug studies, 1 out of 1000 people taking the placebo (inactive substance) showed suicidality compared to approximately 3.5 out of 1000 people who took an AED. The FDA advisory panel voted to accept the FDA’s data at its meeting on July 10.

  • Taking antiepileptic medicines may increase the risk of having suicidal thoughts or actions;
  • Do not make any changes to the medication regimen without first talking with the responsible healthcare professional;
  • Pay close attention to any day-to-day changes in mood, behavior and actions. These changes can happen very quickly so it is important to be mindful of any sudden differences.
  • Be aware of common warning signs that might be a signal for risk of suicide. Some of these are:
    • Talking or thinking about wanting to hurt yourself or end your life
    • Withdrawing from friends and family
    • Becoming depressed or having your depression get worse
    • Becoming preoccupied with death and dying
    • Giving away prized possessions

We again urge patients and families to contact their doctor before stopping an epilepsy medication because this may possibly lead to seizures and worsening of mood.

Zonisamide Side Effects

Visit your doctor or health care professional for regular checks on your progress. Wear a medical identification bracelet or chain to say you have epilepsy, and carry a card that lists all your medications.

It is important to take this medicine exactly as directed. When first starting treatment, your dose will need to be adjusted slowly. It may take weeks or months before your dose is stable. You should contact your doctor or health care professional if your seizures get worse or if you have any new types of seizures. Do not stop taking except on your doctor’s advice. You may develop a severe reaction. Your doctor will tell you how much medicine to take.

You may get drowsy, dizzy, or have blurred vision. Do not drive, use machinery, or do anything that needs mental alertness until you know how this medicine affects you. To reduce dizzy or fainting spells, do not sit or stand up quickly, especially if you are an older patient. Alcohol can increase drowsiness and dizziness. Avoid alcoholic drinks.

Avoid extreme heat. This medicine can cause you to sweat less than normal. Your body temperature could increase to dangerous levels, which may lead to heat stroke.

This medicine may increase the chance of developing metabolic acidosis. If left untreated, this can cause kidney stones, bone disease, or slowed growth in children. Symptoms include breathing fast, fatigue, loss of appetite, irregular heartbeat, or loss of consciousness. Call your doctor immediately if you experience any of these side effects. Also, tell your doctor about any surgery you plan on having while taking this medicine since this may increase your risk for metabolic acidosis.

This medicines may increase the risk of kidney stones. Drinking 6 to 8 glasses of water a day may help prevent the formation of kidney stones.

The use of this medicine may increase the chance of suicidal thoughts or actions. Pay special attention to how you are responding while on this medicine. Any worsening of mood, or thoughts of suicide or dying should be reported to your health care professional right away.

Women who become pregnant while using this medicine may enroll in the North American Antiepileptic Drug Pregnancy Registry by calling 1-888-233-2334. This registry collects information about the safety of antiepileptic drug use during pregnancy.

Zonisamide Endo 100 mg hard capsules

Body weight

Zonisamide may cause weight loss. A dietary supplement or increased food intake may be considered if the patient is losing weight or is underweight whilst on this medication. If substantial undesirable weight loss occurs, discontinuation of Zonisamide should be considered. Weight loss is potentially more serious in children (see section 4.4. Paediatric Population).

Paediatric Population

The warnings and precautions mentioned above are also applicable to adolescent and paediatric patients. The warnings and precautions mentioned below are more relevant to paediatric and adolescent patients.

Heat stroke and dehydration

Preventing overheating and dehydration in children

Zonisamide can cause children to sweat less and overheat and if the child is not treated this can lead to brain damage and death. Children are most at risk especially in hot weather

When a child is taking Zonisamide

• The child should stay cool especially in hot weather

• The child must avoid heavy exercise especially when the weather is hot

• The child must drink plenty of cold water

• The child must not take any of these medicines:

Carbonic anhydrase inhibitors (like topiramate and acetazolamine), and anticholinergic agents (like clomipramine, hydroxyzine, diphenhydramine, haloperidol, imipramine and oxybutynin).


The skin feels very hot with little or no sweating, or the child becomes confused or has muscle cramps, or the child’s heartbeat or breathing become rapid.

• Take the child to a cool, shaded place

• Keep the child’s skin cool with water

• Give the child cold water to drink

Cases of decreased sweating and elevated body temperature have been reported mainly in paediatric patients. Heat stroke requiring hospital treatment was diagnosed in some cases. Heat stroke requiring hospital treatment and leading to death has been reported. Most reports occurred during periods of warm weather. Physicians should discuss with patients and their carers the potential seriousness of heatstroke, situations in which it might arise, as well as action to take in the event of any signs or symptoms. Patients or their carers must be warned to take care to maintain hydration and avoid exposure to excessive temperatures and strenuous physical exercise depending on the condition of the patient. Prescribers should draw the attention of paediatric patients and their parent/carers to the advice in the Packaging Leaflet on preventing heatstroke and overheating in children as provided. In the event of signs or symptoms of dehydration, oligohydrosis, or elevated body temperature, discontinuation of Zonisamide should be considered.

Zonisamide should not be used as co-medication in paediatric patients with other medicinal products that predispose patients to heat related disorders; these include carbonic anhydrase inhibitors and medicinal products with anticholinergic activity.

Body weight

Weight loss leading to deterioration of general condition and failure to take anti-epilepsy medication has been related to a fatal outcome (see section 4.8). Zonisamide is not recommended for paediatric patients who are underweight (definition in accordance with the WHO age adjusted BMI categories) or have a decreased appetite.

The incidence of decreased body weight is consistent across age groups (see section 4.8); however, given the potential seriousness of weight loss in children, weight should be monitored in this population. A dietary supplement or increased food intake should be considered if the patient is failing to gain weight in accordance with growth charts, otherwise Zonisamide should be discontinued.

There are limited data from clinical studies in patients with a body weight of less than 20 kg. Therefore children aged 6 years and above with a body weight of less than 20 kg should be treated with caution. The long term effect of weight loss in the paediatric population on growth and development is unknown.

Metabolic acidosis

The risk of zonisamide induced metabolic acidosis appears to be more frequent and severe in paediatric and adolescent patients. Appropriate evaluation and monitoring of serum bicarbonate levels should be carried out in this population (see section 4.4 – Metabolic acidosis for full warning; see section 4.8 for incidence of low bicarbonate). The long term effect of low bicarbonate levels on growth and development is unknown.

Zonisamide should not be used as co-medication in paediatric patients with other carbonic anhydrase inhibitors such as topiramate and acetazolamide (see section 4.5).

Kidney stones

Kidney stones have occurred in paediatric patients (see section 4.4 Kidney stones for full warning).

Some patients, especially those with a predisposition to nephrolithiasis, may be at increased risk for renal stone formation and associated signs and symptoms such as renal colic, renal pain or flank pain. Nephrolithiasis may lead to chronic kidney damage. Risk factors for nephrolithiasis include prior stone formation, a family history of nephrolithiasis and hypercalciuria. None of these risk factors can reliably predict stone formation during zonisamide treatment.

Increasing fluid intake and urine output may help reduce the risk of stone formation, particularly in those with predisposing risk factors. Renal ultrasound should be performed at the discretion of the physician. In the event kidney stones are detected, Zonisamide should be discontinued.

Hepatic dysfunction

Increased levels of hepatobiliary parameters such as alanine aminotransferase (ALT), aspartate aminotransferease (AST), gamma-glutamyltransferase (GGT) and bilirubin have occurred in paediatric and adolescent patients, without any consistent pattern in the observations of values above the upper limit of normal. Nevertheless, if a hepatic event is suspected, liver function should be evaluated and discontinuation of Zonisamide should be considered.


Cognitive impairment in patients affected by epilepsy has been associated with the underlying pathology and/or the administration of anti-epileptic treatment. In a zonisamide placebo-controlled study conducted in paediatric and adolescent patients, the proportion of patients with impaired cognition was numerically greater in the zonisamide group compared with the placebo group.


Generic name: Zonisamide

Available as: Zonegran: capsules 25mg, 50mg, 100mg.


Average total daily dose: From 18 years: 300mg – 500mg daily divided into 1 or 2 doses.

Doses per day: 1 – 2

Treatment: Add-on therapy for focal seizures with or without secondary generalisation.

Most common possible side effects include the following. Report severe reactions, such as a skin rash, to your doctor.
Skin rash. Nausea, diarrhoea, abdominal pain, constipation, indigestion, anorexia, weight loss, drowsiness, dizziness, confusion, agitation, irritability, depression, psychosis, and unsteadiness.


Average total daily dose: From 6 years. Body weight 20 – 55kg: 6 – 8mg/kg daily. Body weight over 55kg: 300 – 500mg daily.

Doses per day: 1

Treatment: Add-on therapy for partial seizures with or without secondary generalisation.

Most common possible side effects include the following. Report severe reactions, such as a skin rash, to your doctor.
Skin rash. Nausea, diarrhoea, abdominal pain, constipation, indigestion, anorexia, weight loss, drowsiness, dizziness, confusion, agitation, irritability, depression, psychosis, and unsteadiness.

<Back to list of anti-epileptic drugs

Please note:

  • This information is a guide only, and lists the usual daily doses of anti-epileptic drugs (AEDs). The dose taken may be different to those listed above.

  • Treatment of neonatal seizures (from birth to 28 days of age) is not covered.

  • Most doses are listed as ‘mg/kg’: this means milligrams of AED per kg of the child’s weight.

  • Children starting AED treatment at the age of 12 may start on adult doses. Some AEDs are only used for children aged 12 and over (including eslicarbazepine acetate, lacosamide, perampanel, pregabalin, retigabine and tiagabine).

  • Some AED doses are listed as ‘twice daily’ (for example ‘5mg/kg twice daily’). This means that the dose listed is taken each time (and so the total daily dose will be double that listed).

  • Some AED doses are listed as ‘divided into 2 (or 3) doses’ (for example ‘25 – 30mg/kg daily divided into 2 doses’). This means that the total amount listed is divided into two to give the dose taken each time.

  • ‘Effective’ means the seizures it works for. ‘Monotherapy’ means the AED is taken on its own. ‘Add-on therapy’ means the AED is taken alongside other AEDs. ‘Tolerance’ means that a drug becomes less effective the longer you take it.

  • Information for this page comes from sources including the British National Formulary (BNF), the British National Formulary for children (BNFC) and the electronic medicines Compendium (eMC). The side effects listed here are some of the most common possible side effects and may be worded differently in the patient information leaflet for the AED. Doctors may refer to the BNF/BNFC for starting doses and how to increase doses. For more details, and a complete list of side effects, visit new window).

  • Every effort is made to ensure that all information is correct at time of publishing but information may change after publication. This information is not a substitute for advice from your doctor. Epilepsy Society is not responsible for any actions taken as a result of using this information.

What is Zonegran used for?

  • Epilepsy. Zonegran is used to treat partial seizures with or without secondary generalisation. It may be used on its own to treat adults with newly diagnosed epilepsy. It can also be added to existing treatment for adults and children aged six years and over whose current antiepileptic treatment is not fully controlling the seizures.

How does Zonegran work?

Zonegran capsules contain the active ingredient zonisamide, which is a medicine that is used to treat epilepsy. It works by stabilising electrical activity in the brain.

The brain and nerves are made up of many nerve cells that communicate with each other through electrical signals. These signals must be carefully regulated for the brain and nerves to function properly. When abnormally rapid and repetitive electrical signals build up and spread through the brain, the brain becomes over-stimulated and normal function is disturbed. This can result in seizures or fits.

Zonisamide prevents epileptic fits by preventing the excessive electrical activity in the brain. It is not fully understood how zonisamide works, but it is thought to act on sodium and calcium channels found on the nerve cells in the brain. Sodium needs to move into the nerve cells for an electrical signal to build up and then be passed on to other nerve cells. Zonisamide may prevent sodium from entering the nerve cells when they begin to fire abnormally rapid and repetitive electrical signals. This helps stabilise the electrical activity in the brain and prevent the excessive seizure-causing signals from spreading through the brain.

Zonisamide may also affect the activity of a neurotransmitter called GABA. Neurotransmitters are natural body chemicals that are stored in nerve cells. They are also involved in transmitting messages between the nerve cells. GABA is a neurotransmitter that acts as a natural ‘nerve calming’ agent. It helps keep the nerve activity in the brain in balance. Zonisamide may enhance the activity of GABA and so help calm the nerve activity in the brain.

Zonisamide is used to prevent partial seizures, and partial seizures that spread to secondary generalised seizures.

How do I take Zonegran?

  • The dose of this medicine that is prescribed and how often to take it will vary from person to person. It depends on factors such as what other medicines you are taking and how well your seizures are controlled. For children it also depends on body weight, so the dose will need to change as the child grows. It is important to follow the instructions given by your doctor. These will also be printed on the dispensing label that your pharmacist has put on the packet of medicine. If you are unclear about anything you should talk to your pharmacist.
  • Zonegran capsules may be taken either with or without food. The capsules should be swallowed whole with a drink of water.
  • Try to always take your medicine at the same times. If you forget to take a dose don’t worry, just take your next dose as usual when it is due. Do not take a double dose to make up for a missed dose.
  • It is important that people with epilepsy take their medication regularly, as directed by the doctor, because missing doses can trigger seizures in some people. If you have trouble remembering to take your medicine you should ask your pharmacist for advice. You may find a pill reminder box helpful.
  • You should not suddenly stop taking this medicine without consulting your doctor, as this may result in your seizures returning or getting worse. If it is decided that you should stop taking this medicine, the dose should usually be reduced gradually at weekly intervals. Follow the instructions given by your doctor.

Important information about Zonegran

  • This medicine may cause drowsiness or difficulty concentrating, particularly when first starting treatment or after a dose increase. If affected, you should take care when performing potentially hazardous tasks, such as driving or operating machinary.
  • Zonisamide can make you sweat less, which can make your body temperature increase. For this reason it is important to make sure you drink sufficient water while you are taking this medicine, particularly in warm weather or when doing exercise. Drinking water helps keep the body cool and prevent you overheating. Children are particularly at risk of overheating and dehydration, which if not treated can lead to brain damage and death. It is important that children taking this medicine stay cool and avoid doing strenuous exercise, particularly in hot weather. Give them plenty of cold drinks and always get advice from a pharmacist before giving them any other medicines, as some may increase the chance of overheating (see end of factsheet). If your child’s skin feels very hot with little or no sweating, or they become confused, have muscle cramps, or a rapid heartbeat or breathing, you need to cool them down and get urgent medical assistance. Take them to a cool, shaded place, sponge their skin with cool (not cold) water and give them cold water to drink while you are waiting for help. Ask your doctor or pharmacist for more information and advice about this.
  • Zonisamide may increase the risk of kidney stones, particularly if you have a history of kidney stones, or if you are taking other medicines that can cause this side effect (see end of factsheet). Making sure you drink sufficient water reduces the risk of developing kidney stones. Consult your doctor if you get a sudden pain in your back or stomach, have pain on urinating, or notice blood in your urine, as this may be a sign of kidney stones.
  • This medicine can cause loss of appetite and weight loss and people taking it should be weighed regularly. If you are losing too much weight your doctor will ask you to increase the amount of food you are eating, or may prescribe dietary supplements. Children should be weighed every month while they are taking this medicine. If they are not gaining weight as they should be this medicine may need to be stopped.
  • There may be a small increased risk of suicidal thoughts and behaviour in people taking antiepileptic medicines such as zonisamide for any condition. For this reason, it is very important to seek medical advice if you, or someone else taking this medicine, experience any changes in mood or behaviour, distressing thoughts, or feelings about suicide or self-harm at any point while taking this medicine. For more information speak to your doctor or pharmacist.
  • If you develop an unexplained rash, skin peeling, itching, blistering or other unexplained skin reaction while taking this medicine you should consult your doctor, because on very rare occasions this medicine can cause potentially serious skin reactions.

Zonegran should be used with caution in

  • Elderly people.
  • Children under 12 years of age. (Young children are more at risk of side effects, in particular overheating – see warnings above).
  • Children weighing less than 20kg.
  • People who are underweight (see warning above).
  • Decreased liver function.
  • Decreased kidney function.
  • People with personal or family history of kidney stones (see warning above).
  • People who have a high level of calcium in their urine.

Zonegran should not be used in

  • People who are allergic to other medicines from the sulphonamide group, for example, the antibiotic sulfamethoxazole; thiazide diuretics such as bendroflumethiazide; and sulfonylurea medicines for diabetes such as gliclazide.
  • This medicine is not recommended for people with severe liver problems.
  • This medicine is not recommended for children who are underweight or who have a small appetite.
  • This medicine is not recommended for children under six years of age because its safety and effectiveness have not been studied in this age group.

This medicine should not be used if you are allergic to one or any of its ingredients. Please inform your doctor or pharmacist if you have previously experienced such an allergy.

If you feel you have experienced an allergic reaction, stop using this medicine and inform your doctor or pharmacist immediately.

Pregnancy and breastfeeding

Certain medicines should not be used during pregnancy or breastfeeding. However, other medicines may be safely used in pregnancy or breastfeeding providing the benefits to the mother outweigh the risks to the unborn baby. Always inform your doctor if you are pregnant or planning a pregnancy, before using any medicine.

  • It is very important for women with epilepsy to talk to the doctor responsible for their epilepsy treatment about getting pregnant and planning a family. Antiepileptic medicines are associated with an increased risk of developmental disorders and malformations in the baby. However, stopping antiepileptic treatment during pregnancy runs the risk of the mother having seizures, which can harm both the mother and the developing baby. This risk may be higher than that from continuing the medication. It is important that all the risks and benefits of treatment are weighed up. Seek medical advice from your doctor.
  • The manufacturer of this medicine recommends that women who could get pregnant should use an effective method of contraception to avoid pregnancy, both while taking this medicine and for one month after stopping treatment with this medicine.
  • This medicine passes into breast milk. As this could cause side effects in a nursing infant, the manufacturer states that this medicine should not be used by women who are breastfeeding. You should discuss this with your doctor, because it is important that all the risks and benefits of the medicine and breastfeeding are weighed up. If you do breastfeed, the manufacturer recommends that you should not start until one month after stopping this medicine, as it takes this long for the medicine to be fully removed from the body. However, if this is the only antiepileptic you are taking, your doctor may conclude that you can breastfeed earlier, providing the baby is monitored closely. It is important to get medical advice from your doctor.

Possible side effects of Zonegran

Medicines and their possible side effects can affect individual people in different ways. The following are some of the side effects that are known to be associated with this medicine. Just because a side effect is stated here does not mean that all people using this medicine will experience that or any side effect.

Very common (affect more than 1 in 10 people)

  • Loss of appetite.
  • Sleepiness.
  • Dizziness.
  • Shaky movements and unsteady walk (ataxia).
  • Agitation.
  • Irritability.
  • Confusion.
  • Depression.
  • Memory problems.
  • Double vision.

Common (affect between 1 in 10 and 1 in 100 people)

  • Weight loss.
  • Kidney stones – see warning section above.
  • Disturbances of the gut, such as diarrhoea, constipation, abdominal pain, indigestion, nausea.
  • Mood swings.
  • Anxiety.
  • Difficulty sleeping (insomnia).
  • Problems with speech, thinking or attention.
  • Rash or itching.
  • Hair loss.
  • Fever.
  • Flu-like symptoms.
  • Fatigue.
  • Swollen ankles due to fluid retention (peripheral oedema).

Uncommon (affect between 1 in 100 and 1 in 1000 people)

  • Pneumonia.
  • Urinary tract infection.
  • Feelings of anger or aggression.
  • Suicidal thoughts or behaviour – see warning section above.
  • Gallstones.
  • Low levels of potassium in the blood (hypokalaemia).

Very rare (affect fewer than 1 in 10,000 people)

  • Decreased sweating and heatstroke. See warning section above.
  • Severe blistering or peeling skin reactions, such as Stevens Johnson syndrome or toxic epidermal necrolysis. See warning section above.
  • Disturbances in the normal levels of blood cells in the blood. You should consult your doctor immediately if you experience any of the following symptoms, because they may indicate a problem with your blood cells: unexplained bruising or bleeding, purple spots, sore throat, mouth ulcers, high temperature (fever), feeling tired or general illness. Your doctor may want to take a blood test to check your blood cells.
  • Inflammation of the pancreas (pancreatitis). Tell your doctor if you get severe abdominal pain while taking this medicine.
  • Increased acid levels in the blood (metabolic acidosis). Symptoms may include headaches, drowsiness, shortness of breath and loss of appetite; tell your doctor if you experience these.
  • Muscle breakdown (rhabdomyolysis). Tell your doctor if you experience any unexplained muscular symptoms such as pain, tenderness, cramps, or weakness while taking this medicine, particularly if accompanied by a fever or feeling generally unwell. Your doctor may need to check for side effects on the muscles by taking a blood test to measure the level of a compound called creatinine kinase in your blood.
  • Kidney failure.
  • Liver damage.
  • Hallucinations.

The side effects listed above may not include all of the side effects reported by the medicine’s manufacturer. For more information about any other possible risks associated with this medicine, please read the information provided with the medicine or consult your doctor or pharmacist.

If you think you have experienced a side effect from a medicine or vaccine you should check the patient information leaflet. This lists the known side effects and what to do if you get them. You can also get advice from your doctor, nurse or pharmacist. If they think it’s necessary they’ll report it for you.

You can also report side effects yourself using the yellow card website:

How can Zonegran affect other medicines?

It is important to tell your doctor or pharmacist what medicines you or your child are already taking, including those bought without a prescription and herbal medicines, before you start treatment with this medicine. Similarly, check with your doctor or pharmacist before using any new medicines while using this one, to make sure that the combination is safe.

If this medicine is taken in combination with other medicines that can reduce sweating and raise body temperature, for example those listed below, there may be an increased risk of raised body temperature and possibly heat stroke, particularly in warm weather. These medicine should not be given to children taking this medicine and should be used with caution in adults:

  • antimuscarinic medicines for urinary incontinence, for example oxybutynin, flavoxate, tolterodine, propiverine, trospium
  • antimuscarinic medicines for Parkinson’s symptoms, eg procyclidine
  • antipsychotic medicines, for example olanzapine, haloperidol, chlorpromazine, clozapine
  • antispasmodic medicines, eg hyoscine, atropine
  • carbonic anhydrase inhibitors, for example acetazolamide, topiramate
  • sedating antihistamines, eg brompheniramine, chlorphenamine, hydroxyzine, diphenhydramine, promethazine
  • some antisickness medicines, eg promethazine, cyclizine, hyoscine
  • tricyclic antidepressants such as clomipramine, imipramine.

There may be an increased risk of developing kidney stones if this medicine is taken in combination with other medicines that can have this side effect, for example topiramate, acetazolamide.

The following medicines may decrease the amount of zonisamide in your blood. If you start or stop treatment with any of these your doctor may need to adjust your dose of zonisamide:

  • carbamazepine
  • phenobarbital
  • phenytoin
  • rifampicin.

It is recommended that people who are taking any antiepileptic medicines should avoid taking the herbal remedy St John’s wort (Hypericum perforatum). This is because St John’s wort may affect the level of antiepileptic medicines in the blood and could increase the risk of seizures.

Other medicines containing the same active ingredient

There are currently no other medicines available in the UK that contain zonisamide as the active ingredient.

Further reading

For background information about our medicine factsheets, including the references used to produce them, .

Last updated 04.11.2013


For over 80 years, the most effective treatment for epilepsy and seizure disorders has been through the use of seizure-preventing medications called anti-convulsant or anti-epileptic drugs (AEDs).

While these medications do not cure epilepsy, they make it possible for many people to live normal, active lives completely free of seizures. Other people may continue to have seizures, but less frequently. And there are still those who need other treatment methods as the drugs are not effective against their seizures.

There is much variability among people and the AEDs they take including side effects and the drug’s effectiveness against their type of seizures. It often takes a good deal of time to find the right medication (mono therapy), or combination of medication (polytherapy), in the right dosage to reach an effective seizure-preventing level in a person.

It is important to remember that these medications will only work if they are taken regularly, every day! To help the medicine work, here are some suggestions:

  • Take the medicine at the same time every day;
  • Take the exact amount of medicine that the doctor has said–changing your dose on your own might cause you to have a seizure;
  • If medicine is a liquid, shake the bottle well before you pour the dose to ensure that the medication is properly distributed in the liquid;
  • Keep your medicines in a cool, dry place, out of children’s reach;
  • Report any side effects and seizure activity to your doctor, he/she may want to try a different dose or a different medication altogether;
  • Ask your doctor ahead of time what to do if you miss a dose of medication;
  • Don’t run out of medication–renew your prescription in a timely manner so you always have at least a week’s supply on hand;
  • Ask your doctor ahead of time if there are any over-the-counter medicines (ex: cold pills, pain medicines), herbal products, vitamins or dietary supplements that you should not take because you are taking epilepsy medications;
  • Be careful when consuming alcohol–check with your doctor about how it may mix with your medicine;
  • Get enough sleep–lack of sleep is thought to trigger seizures.

Some common medicines for epilepsy include:

  1. Ativan (Brand name)/Lorazepam (Generic). Some side effects: drowsiness, sleepiness, fatigue, poor coordination, unsteadiness, behavior changes
  2. Banzel (Brand name)/Rufinamide (Generic). Some side effects: headache, dizziness, fatigue, sleepiness, double vision, tremors, hypersensitivity syndrome, fever, rash, fluid accumulation, swollen lymph nodes, liver injury and confusion
  3. Carbatrol (Brand name)/Extended Release Carbamazepine (Generic). Some side effects: dizziness, drowsiness, blurred or double vision, nausea, skin rashes, abnormal blood counts (rare)
  4. Depakene (Brand name)/Valproate (Generic), introduced in 1978. Some side effects: upset stomach, altered bleeding time, liver toxicity, hair loss, weight gain, tremor
  5. Depakote (Brand name)/Divalproex Sodium (Generic). Some side effects: upset stomach, altered bleeding time, liver toxicity, hair loss, weight gain, tremor
  6. Diamox (Brand name)/Acetazolamide (Generic). Some side effects: appetite loss, frequent urination, drowsiness, confusion, numbness of extremities, kidney stones
  7. Dilantin (Brand name)/Phenytoin (Generic), introduced in 1938. Some side effects: clumsiness, insomnia, motor twitching, nausea, rash, gum overgrowth, hairiness, thickening of features
  8. Felbatol (Brand name)/ Felbamate (Generic), introduced in 1993. Some side effects: anorexia, vomiting, insomnia, nausea, headache, liver and blood toxicity
  9. Gabitril (Brand name)/Tiagabine (Generic), introduced in 1997. Some side effects: tremors, dizziness, nervousness, difficulty concentrating, sleepiness, weakness
  10. Keppra (Brand name)/Levetiracetam (Generic). Some side effects: sleepiness, fatigue, poor coordination, loss of strength, dizziness
  11. Klonopin (Brand name)/Clonazepam (Generic), introduced in 1975. Some side effects: drowsiness, sleepiness, fatigue, poor coordination, unsteadiness, behavior changes
  12. Lamictal (Brand name)/Lamotrigine (Generic), introduced in 1994. Some side effects: dizziness, headache, blurred vision, clumsiness, sleepiness, nausea, skin rash
  13. Lyrica (Brand name)/Pregabalin (Generic).Some side effects: dizziness, somnolence, ataxia, asthenia, weight gain
  14. Mysoline (Brand name)/Primidone (Generic), introduced in 1954. Some side effects: clumsiness, dizziness, appetite loss, fatigue, drowsiness, hyper-irritability, insomnia, depression, hyperactivity (children)
  15. Neurontin (Brand name)/Gabapentin (Generic), introduced in 1993. Some side effects: sleepiness, dizziness, clumsiness, fatigue, twitching
  16. Onfi (Brand name)/Clobazam (Generic), FDA approval in June of 2011. Some side effects: somnolence, sedation, drooling, constipation, cough, dysphagia, fatigue
  17. Potiga (Brand name)/Ezogabine (Generic),Some side effects: suicidal thoughts, dizziness, vertigo, fatigue, confusion, tremors, double vision, memory problems, alertness, problems with coordination, increased urinary retention
  18. Phenobarbital (Brand name)/Phenobarbital (Generic), introduced in 1912. Some side effects: drowsiness, irritability, hyperactivity (children), behavioral problems, difficulty concentrating, depression
  19. Phenytek (Brand name)/Extended Phenytoin Sodium (Generic). Some side effects: clumsiness, insomnia, motor twitching, nausea, rash, gum overgrowth, hairiness, thickening of features
  20. Sabril (Brand name)/Vigabatrin (Generic). Some side effects: sleepiness, headache, dizziness, nervousness, hyperactivity in children
  21. Tegretol (Brand name)/Carbamazepine (Generic), introduced in 1974. Some side effects: dizziness, drowsiness, blurred or double vision, nausea, skin rashes, abnormal blood counts (rare)
  22. Tegretol XR (Brand name)/Extended Release Carbamazepine (Generic). Some side effects: dizziness, drowsiness, blurred or double vision, nausea, skin rashes, abnormal blood counts (rare)
  23. Topamax (Brand name)/Topiramate (Generic), introduced in 1996. Some side effects: confusion, sleepiness, dizziness, clumsiness, difficulty thinking or talking, tingling sensation of the skin, nausea, decreased appetite
  24. Tranxene (Brand name)/Clorazepate (Generic), introduced in 1981. Some side effects: drowsiness, sleepiness, fatigue, poor coordination, unsteadiness, behavior changes
  25. Trileptal (Brand name)/Oxcarbazepine (Generic). Some side effects: difficulty concentrating, sleepiness, fatigue, dizziness, double vision, nausea, unsteadiness, rash
  26. Vimpat (Brand name)/Lacosamide (Generic). Some side effects: dizziness, headaches, nausea, vomiting, double vision, sleepiness, fatigue, unsteadiness, shakiness, memory loss, mood changes, electrocardiogram changes
  27. Zarontin (Brand name)/Ethosuximide (Generic), introduced in 1960. Some side effects: appetite loss, nausea, drowsiness, headache, dizziness, fatigue, rash, abnormal blood counts (rare)
  28. Zonegran (Brand name)/Zonisamide (Generic). Some side effects: sleepiness, dizziness, loss of appetite, headache, nausea, irritability, difficulty concentrating, unsteadiness, fever, kidney stones, rash (should not be used in individuals allergic to sulfa drugs)

The following medicine is not prescribed for daily, long-term use, but to stop episodes of prolonged or cluster seizures:

Diastat (Brand name)/Diazepam Rectal Gel (Generic). Some side effects: drowsiness, sleepiness, fatigue, poor coordination, unsteadiness, behavior changes



The most common adverse reactions with ZONEGRAN (an incidence at least 4% greater than placebo) in controlled clinical trials and shown in descending order of frequency were somnolence, anorexia, dizziness, ataxia, agitation/irritability, and difficulty with memory and/or concentration.

In controlled clinical trials, 12% of patients receiving ZONEGRAN as adjunctive therapy discontinued due to an adverse reaction compared to 6% receiving placebo. Approximately 21% of the 1,336 patients with epilepsy who received ZONEGRAN in clinical studies discontinued treatment because of an adverse reaction. The most common adverse reactions leading to discontinuation were somnolence, fatigue and/or ataxia (6%), anorexia (3%), difficulty concentrating (2%), difficulty with memory, mental slowing, nausea/vomiting (2%), and weight loss (1%). Many of these adverse reactions were doserelated (see WARNINGS and PRECAUTIONS).

Adverse Reaction Incidence In Controlled Clinical Trials

Table 4 lists adverse reactions that occurred in at least 2% of patients treated with ZONEGRAN in controlled clinical trials that were numerically more common in the ZONEGRAN group. In these studies, either ZONEGRAN or placebo was added to the patient’s current AED therapy.

Table 4. Adverse Reactions in Placebo-Controlled, Add-On Trials (Events that occurred in at least 2% of ZONEGRANtreated patients and occurred more frequently in ZONEGRAN-treated than placebo-treated patients)

ZONEGRAN (n=269)
PLACEBO (n=230)
Headache 10 8
Abdominal Pain 6 3
Flu Syndrome 4 3
Anorexia 13 6
Nausea 9 6
Diarrhea 5 2
Dyspepsia 3 1
Constipation 2 1
Dry Mouth 2 1
Ecchymosis 2 1
Weight Loss 3 2
Dizziness 13 7
Ataxia 6 1
Nystagmus 4 2
Paresthesia 4 1
Confusion 6 3
Difficulty Concentrating 6 2
Difficulty with Memory 6 2
Mental Slowing 4 2
Agitation/Irritability 9 4
Depression 6 3
Insomnia 6 3
Anxiety 3 2
Nervousness 2 1
Schizophrenic/Schizophreniform Behavior 2 0
Somnolence 17 7
Fatigue 8 6
Tiredness 7 5
Speech Abnormalities 5 2
Difficulties in Verbal Expression 2 <1
Rhinitis 2 1
Rash 3 2
Diplopia 6 3
Taste Perversion 2 0

Other Adverse Reactions In Clinical Trials

ZONEGRAN has been administered to 1,598 individuals during all clinical trials, only some of which were placebo-controlled. The frequencies represent the proportion of the 1,598 individuals exposed to ZONEGRAN who experienced an event on at least one occasion. All events are included except those already listed in the previous table or discussed in WARNINGS or PRECAUTIONS, trivial events, those too general to be informative, and those not reasonably associated with ZONEGRAN.

Events are further classified within each category and listed in order of decreasing frequency as follows: frequent occurring in at least 1:100 patients; infrequent occurring in 1:100 to 1:1000 patients; rare occurring in fewer than 1:1000 patients.

Body As A Whole

Frequent: Accidental injury, asthenia. Infrequent: Chest pain, flank pain, malaise, allergic reaction, face edema, neck rigidity. Rare: Lupus erythematosus.


Infrequent: Palpitation, tachycardia, vascular insufficiency, hypotension, hypertension, thrombophlebitis, syncope, bradycardia. Rare: Atrial fibrillation, heart failure, pulmonary embolus, ventricular extrasystoles.


Frequent: Vomiting. Infrequent: Flatulence, gingivitis, gum hyperplasia, gastritis, gastroenteritis, stomatitis, cholelithiasis, glossitis, melena, rectal hemorrhage, ulcerative stomatitis, gastro-duodenal ulcer, dysphagia, gum hemorrhage. Rare: Cholangitis, hematemesis, cholecystitis, cholestatic jaundice, colitis, duodenitis, esophagitis, fecal incontinence, mouth ulceration.

Hematologic And Lymphatic

Infrequent: Leukopenia, anemia, immunodeficiency, lymphadenopathy. Rare: Thrombocytopenia, microcytic anemia, petechia.

Metabolic And Nutritional

Infrequent: Peripheral edema, weight gain, edema, thirst, dehydration. Rare: Hypoglycemia, hyponatremia, lactic dehydrogenase increased, SGOT increased, SGPT increased.

Infrequent: Leg cramps, myalgia, myasthenia, arthralgia, arthritis.

Nervous System

Frequent: Tremor, convulsion, abnormal gait, hyperesthesia, incoordination. Infrequent: Hypertonia, twitching, abnormal dreams, vertigo, libido decreased, neuropathy, hyperkinesia, movement disorder, dysarthria, cerebrovascular accident, hypotonia, peripheral neuritis, reflexes increased. Rare: Dyskinesia, dystonia, encephalopathy, facial paralysis, hypokinesia, hyperesthesia, myoclonus, oculogyric crisis.

Behavioral Abnormalities –Non-Psychosis -Related

Infrequent: Euphoria.

Frequent: Pharyngitis, cough increased. Infrequent: Dyspnea. Rare: Apnea, hemoptysis.

Skin And Appendages
Special Senses

Infrequent: Urinary frequency, dysuria, urinary incontinence, hematuria, impotence, urinary retention, urinary urgency, amenorrhea, polyuria, nocturia. Rare: Albuminuria, enuresis, bladder pain, bladder calculus, gynecomastia, mastitis, menorrhagia.

Post Marketing Experience

The following serious adverse reactions have been reported since approval and use of ZONEGRAN worldwide. These reactions are reported voluntarily from a population of uncertain size; therefore, it is not possible to estimate their frequency or establish a causal relationship to drug exposure.

Acute pancreatitis, rhabdomyolysis, increased creatine phosphokinase, and drug reaction with eosinophilia and systemic symptoms (DRESS) (see WARNINGS).

To report SUSPECTED ADVERSE REACTIONS, contact Concordia Pharmaceuticals Inc. at 1- 877-370-1142 or the FDA at 1-800-FDA-1088 or

Read the entire FDA prescribing information for Zonegran (Zonisamide)

Zonegran Side Effects

Generic Name: zonisamide

Medically reviewed by Last updated on Jan 24, 2019.

  • Overview
  • Side Effects
  • Dosage
  • Professional
  • Interactions
  • More

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

For the Consumer

Applies to zonisamide: oral capsule

Along with its needed effects, zonisamide (the active ingredient contained in Zonegran) 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 zonisamide:

More common

  • Discouragement
  • feeling sad or empty
  • irritability
  • lack of appetite
  • loss of interest or pleasure
  • mood or mental changes
  • shakiness or unsteady walking
  • tiredness
  • trouble with concentrating
  • trouble with sleeping

Less common

  • Agitation
  • bruising
  • delusions
  • hallucinations
  • large, flat blue or purplish patches on the skin
  • rash

Some side effects of zonisamide 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:

More common

  • Abdominal or stomach pain
  • anxiety
  • difficulty with memory
  • dizziness
  • double vision
  • headache
  • loss of appetite
  • nausea
  • restlessness
  • sleepiness
  • unusual drowsiness
  • unusual tiredness or weakness

Less common

  • Aching muscles or joints
  • acid or sour stomach
  • bad, unusual, or unpleasant taste in the mouth
  • belching
  • change in taste
  • chills
  • constipation
  • diarrhea
  • difficulty with speaking
  • difficulty with thinking
  • dry mouth
  • fever
  • general ill feeling
  • headache
  • heartburn
  • indigestion
  • mental slowness
  • nervousness
  • runny or stuffy nose
  • sneezing
  • tingling, burning, or prickly feelings on the skin
  • uncontrolled, back and forth, or rolling eye movements
  • weight loss

For Healthcare Professionals

Applies to zonisamide: oral capsule


The most common adverse reactions to this drug are somnolence, dizziness, and anorexia.


Very common (10% or more): Anorexia (13%)

Common (1% to 10%): Abdominal pain, nausea, diarrhea, dyspepsia, constipation, dry mouth

Nervous system

Very common (10% or more): Somnolence (17%), dizziness (13%), headache (10%), ataxia

Common (1% to 10%): Paresthesia, fatigue, tiredness, bradyphrenia, tremor

Uncommon (0.1% to 1%): Convulsion

Very rare (less than 0.01%): Coma, grand mal seizure, myasthenic syndrome, neuroleptic malignant syndrome, status epilepticus

Postmarketing reports: Restless legs syndrome


Common (1% to 10%): Speech abnormalities, difficulties in verbal expression, taste perversion


Very common (10% or more): Agitation, irritability, confusional state, depression

Common (1% to 10%): Difficulty concentrating, difficulty with memory, mental slowing, insomnia, anxiety, nervousness, affect liability, psychotic disorder

Uncommon (0.1% to 1%): Anger, aggression, suicidal ideation, suicide attempt

Very rare (less than 0.01%): Hallucination, amnesia, mania


Common (1% to 10%): Nystagmus, diplopia


Common (1% to 10%): Rash

Very rare (less than 0.01%): Drug rash with eosinophilia and systemic symptoms, anhidrosis, erythema multiforme, pruritus, Stevens-Johnson syndrome, toxic epidermal necrolysis


Very common (10% or more): Anorexia

Common (1% to 10%): Weight loss

Very rare (less than 0.01%): Metabolic acidosis

Postmarketing reports: Elevated creatine phosphokinase


Common (1% to 10%): Ecchymosis


Common (1% to 10%): Rhinitis

Uncommon (0.1% to 1%): Pneumonia


Uncommon (0.1% to 1%): Urinary tract infection

Postmarketing reports: Acute pancreatitis


Postmarketing reports: Rhabdomyolysis


Uncommon (0.1% to 1%): Urinary tract infection


Common (1% to 10%): Hypersensitivity

Very rare (less than 0.01%): Drug induced hypersensitivity syndrome


Common (1% to 10%): Influenza syndrome


Very rare (less than 0.01%): Renal tubular acidosis

Frequency not reported: Nephrolithiasis, hydronephrosis, renal failure, urine abnormality

1. Cerner Multum, Inc. “UK Summary of Product Characteristics.” O 0

3. “Product Information. Zonegran (zonisamide)” Elan Pharmaceuticals, S. San Francisco, CA.

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.

Medical Disclaimer

More about Zonegran (zonisamide)

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  • Zonegran (Advanced Reading)

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