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What does it do?

Clozapine is used to treat and prevent schizophrenia. It is also sometimes used for other conditions.

How should you take it?

Take clozapine regularly as directed with a glass of water.
Measure clozapine liquid carefully with an oral syringe or measuring spoon. Shake the bottle well (for 90 seconds when you first start the bottle and then 10 seconds every other time) before measuring each dose.

What if you forget a dose?

Take the missed dose as soon as possible. If it is close to the time for your next dose, skip the missed dose and carry on as normal. Do not take two doses at the same time.
If you miss more than two days in a row, talk to your doctor before you take any more. You will need to start again at a lower dose with weekly blood tests.

Can you take other medicines?

Some medicines available without a prescription may react with clozapine including:

  • some antihistamines or anti-nausea medicines such as promethazine (e.g. Phenergan®), hyoscine (e.g. Scopoderm®), meclozine (e.g. Sea-legs®)
  • trimethoprim

Tell your pharmacist or doctor about all medicines or treatments that you may be taking, including vitamins, herbal products (e.g. St John's wort, kava) or recreational drugs.

What side effects might you notice?

Side EffectsRecommended action

Reduced number of blood cells that fight infections in your body - symptoms include: fever, chills, sore throat or generally feeling unwell


Feeling restless, strange or uncontrolled movements, tremor, stiffness

Fast or irregular heartbeat, chest pain, fainting

Symptoms of a blood clot including: sudden shortness of breath, swelling or pain in one leg


Prolonged erection (longer than four hours)

Tell your doctor immediately


Tell your doctor

Drowsiness, dizziness, weakness, headache, anxiety, blurred vision

Weight gain

More saliva than usual, drooling

Stomach upset

Peeing when you don’t want to, bed-wetting, trouble peeing

Less interest in sex, impotence

Tell your doctor if troublesome

If you notice any other effects, discuss them with your doctor or pharmacist.

Other information:

  • Tell your doctor if you have heart, liver, blood, bowel, bladder or prostate problems.
  • Tell your doctor if you have diabetes, Parkinson’s disease, angle-closure glaucoma, have ever had a seizure, blood clot, stroke or ‘mini-stroke’, or if you have experienced strange body movements with another medicine.
  • Tell your doctor if you are pregnant, planning to become pregnant, or breastfeeding.
  • You will need a blood test before you start taking clozapine, then every week for 18 weeks, and then every four weeks after that while taking clozapine. This is because clozapine can sometimes lower the number of white cells in your blood, making it harder for your body to fight off infections.
  • Your doctor may do a heart test (ECG) before you start and while you are taking clozapine.
  • Clozapine can impair your ability to do tasks such as driving or using machines. Alcohol makes this worse. Discuss your risk with your health professional. (search NZTA - Are you safe to drive?)
  • Smoking can change the effect of clozapine. Tell your doctor if you give up, cut down or start smoking.
  • Clozapine reduces your body’s ability to maintain a normal temperature. Be careful of becoming too cold or too hot. When exercising, drink plenty of water.
  • You have an increased risk of getting diabetes while taking clozapine. Discuss with your doctor.
  • Do not stop taking clozapine without talking to your doctor first.

This leaflet contains important, but not all, information about this medicine.

Prepared by the PILs Committee at Christchurch Hospital, Canterbury District Health Board, New Zealand. October 2020

For more general information about this sheet annd its contents, see: What does a My Medicines sheet cover?

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About My Medicines

My Medicines Patient Information Leaflets (PILs) contain important, but not all, information about the medicines they describe.

For more information about the sheets, see: What does a My Medicines sheet cover?

My Medicines is developed by a team at the Canterbury District Health Board. Our team is made up of doctors, pharmacists, and a non-medical person to help us keep to plain language. We also discuss our information with specialist health professionals or groups when needed