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Zonisamide drug information

Patient information A-Z

Drug/brand names

  • Zonisamide
  • Zonegran


Zonisamide is an antiepileptic drug used to reduce seizure frequency or severity in people who have epilepsy in cases where other antiepileptic medications have failed. It is used to treat focal (partial) seizures that may or may not become generalised (tonic clonic) seizures.

Zonisamide may also be used to treat absence seizures which have not responded to other treatment and myoclonic seizures.


Zonisamide is available in form of 25mg, 50mg and 100mg capsules.

Side effects

(the list of side effects is not exhaustive, please refer to product literature for full list)

Dose-related side effects become more likely the higher the dose of medication and improve if the dose is reduced again. They sometimes occur temporarily when the medication is started or as the dose is increased. If you are also taking other anti-epileptic medication, sometimes reducing them, rather than zonisamide may alleviate these side effects. Usually they settle within eight weeks of starting medication. Please consult you doctor or epilepsy specialist nurse for advice.

Common side effects are:

  • Sleepiness
  • Dizziness
  • Fatigue
  • Memory and concentration problems
  • Loss of appetite
  • Nausea, abdominal pains or heart burn
  • Problems with vision including double vision
  • Problems with balance, co-ordination or speech
  • Constipation or diarrhoea
  • Tremor
  • Rash – if you develop a rash please seek medical attention as soon as possible
  • Swelling of the ankles
  • Zonisamide may cause confusion and mood changes

Less commonly

  • Kidney stones
  • Hair loss
  • Infections and influenza type illnesses
  • Some patients experience difficulties with speech
  • All anti-epileptic medication can cause feelings of depression, or severe mood changes. If you experience any of these please contact your specialist.


  • Liver problems
  • Kidney problems
  • Hallucinations
  • Problems with the blood
  • Heat stroke – patients are advised to ensure that they drink enough fluid when in hot environments or exercising.
  • Severe rash

You should inform your specialist if you have a history of hypersensitivity to a group of drugs known as sulphonamides eg Septrin (co-trimoxazole) or sulfasalazine, as you are more likely to have a reaction to zonisamide.

In the event of any of these side effects, contact the epilepsy nurse (contact details are at the end of the leaflet), and/or your GP.


Zonisamide is not thought to alter the efficacy of the contraceptive pill, three month contraceptive injection or the hormone coil (Mirena).

The manufacturer recommends taking effective contraception until at least one month after stopping taking zonisamide.

Pregnancy and breast feeding

If you are taking any anti-epileptic drug, you should ask to see your specialist and discuss the best preparations and doses before you conceive. Once you are already pregnant it is too late to make these changes. The risks to your baby from zonisamide are not yet known. We therefore recommend that you do not take it if you are contemplating pregnancy.

We generally recommend you take folic acid 5mg daily twelve weeks prior to conception until the end of weeks 12 of pregnancy when taking any antiepileptic medication.

Zonisamide is excreted in human milk and may remain in milk for up to one month after you stop taking zonisamide. It is important to discuss use of zonisamide whilst breast feeding with your specialist before the birth of the baby.

Drug interactions

Ordinary medications such as paracetamol can be taken with zonisamide.

The levels of zonisamide in your body can be altered by some other medication; you will need to be monitored closely if you need to take a medication that affects zonisamide. It is always recommended to remind your doctor or pharmacist that you take zonisamide in order to avoid problems with other medication.

Other useful information

  • You can take zonisamide at the same time as you take other medication.
  • Keep a record of your seizures when you start any new medication. This will help to determine future drug dosages.
  • Store zonisamide below 30 degrees and in the packaging that it comes in.
  • Do not stop taking your medication suddenly and without consultation with your doctor.
  • If you miss a dose, take it as soon as you remember but do not take two doses at the same time or within six hours of each other.

Contact details

If you have any questions or concerns, please contact the epilepsy nurse specialist on 01223 217992.

The information on this leaflet is not exhaustive. Please refer to the patient information leaflet prepared by the manufacturer of your drug which can be found in the medicine packaging.

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Contact us

Cambridge University Hospitals
NHS Foundation Trust
Hills Road, Cambridge

Telephone +44 (0)1223 245151