Clozapine (Clozaril, Denzapine, Zaponex)

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Clozapine is prescribed for mental health problems which affect the way you think, feel or behave.

It is important that you have regular check-ups and blood tests.

Make sure you read all the printed information you are given. If there is anything you are unsure about, ask your doctor or clinic for further advice.

Type of medicineAn antipsychotic medicine
Used forSchizophrenia; psychosis in people with Parkinson's disease
Also calledClozaril®; Denzapine®; Zaponex®
Available asTablets and oral liquid medicine

Clozapine belongs to a group of medicines called antipsychotics. These medicines work on the balance of chemical substances in the brain. You will be prescribed clozapine by a specialist doctor who will keep a thorough and close check on your progress.

Clozapine is prescribed to relieve the symptoms of psychosis. This is the name used by doctors to describe a disordered state of mind. Clozapine is prescribed in particular for people with schizophrenia. Schizophrenia is a mental health problem that causes disordered ideas, beliefs and experiences. People with schizophrenia can have difficulty knowing which thoughts and experiences are true and real and which are not. Similar symptoms to these can also sometimes occur in people who have Parkinson's disease.

Some medicines are not suitable for people with certain conditions, and sometimes a medicine may only be used if extra care is taken. For these reasons, before you start taking clozapine it is important that your doctor knows:

  • If you are pregnant or breast-feeding.
  • If you have a heart condition or blood vessel disease.
  • If you have liver, kidney, or prostate problems.
  • If you have breathing problems.
  • If you have had any surgery on your bowels, or if you have any bowel problems (including severe constipation).
  • If you have any of the following: epilepsy, depression, glaucoma (raised pressure in your eye) or myasthenia gravis (this is a condition which causes muscle weakness).
  • If you have ever had jaundice (yellowing of your skin or the whites of your eyes) or a blood disorder.
  • If you have a tumour on your adrenal gland (a condition called phaeochromocytoma).
  • If you have had an allergic reaction to a medicine.
  • If you are taking or using any other medicines. This includes any medicines you are taking which are available to buy without a prescription, such as herbal and complementary medicines.
  • Before you start the treatment, read the manufacturer's printed information leaflet from inside the pack and the additional information you have been given by your doctor or clinic. These will provide you with more information about clozapine and will include a full list of the side-effects which you may experience from taking it.
  • Your dose will be individually adjusted to control your symptoms, so take clozapine exactly as your doctor tells you to. Try to get into the habit of taking your doses at the same times of day as this will help you avoid missing any. Clozapine is not affected by food in your stomach so you can take your doses either before or after meals.
  • Many people find it helps to swallow the tablet with a drink of water. If you have any difficulties swallowing, let your doctor know about this so that you can be prescribed liquid medicine instead.
  • If you have been given liquid medicine, make sure you understand how to use the dose syringes (dispensers) to measure out your doses. If you are unsure about this, you can ask your clinic or pharmacist to show you what to do. You can mix your dose into a small glass of water if you like, but do not mix it with any other drinks.
  • If you forget to take a dose, take it as soon as you remember unless your next dose is due. If it is nearly time for your next dose, take the next dose when it is due but leave out the forgotten dose. Do not take two doses together to make up for a missed dose. If you miss taking clozapine for more than two days, speak with your clinic for advice, as your dose may need adjusting for a short while.
  • You will need to register with a monitoring service, which will make sure it is safe for you to keep taking clozapine. You will be told how to do this by your clinic.
  • Remember to keep your regular doctor's appointments so that your progress can be checked. It is important that you have regular blood tests while you are being treated with clozapine.
  • Drinking alcohol will increase the chance that you experience side-effects so should be avoided.
  • If you are having an operation, tell the person carrying out the treatment which medicines you are taking. This is important because clozapine may interfere with any anaesthetic you receive.
  • If you buy or take any 'over-the-counter' medicines, check with a pharmacist that they are suitable to take with clozapine.
  • If you have diabetes you may need to check your blood glucose more frequently, as clozapine can affect the levels of sugar in your blood. Your doctor will advise you about this.
  • Smoking may affect the amount of clozapine in your body. Let your doctor know if you start or stop smoking while taking clozapine.
  • Treatment with clozapine is long-term and it is important that you continue to take it for as long as your doctor tells you to. Do not change your dose or stop treatment suddenly as this can cause problems. If a change in your treatment becomes necessary, your doctor will want you to reduce your dose gradually over a week or so.

Along with their useful effects, most medicines can cause unwanted side-effects although not everyone experiences them. Your doctor will discuss the risks of the treatment with you before you start taking clozapine. In particular, clozapine can cause heart problems and blood disorders. You will be given regular check-up appointments so that your doctor can monitor you for any evidence of these.

The table below contains some of the most common unwanted effects associated with clozapine. You will find a full list in the manufacturer's information leaflet supplied with your medicine.

Common clozapine side-effectsWhat can I do if I experience this?
Feeling sleepy, blurred visionDo not drive or use tools or machines. Do not drink alcohol
ConstipationEat a well-balanced diet and drink several glasses of water each day. Let your doctor know if it continues
Feeling faint or dizzy, especially when you sit up or stand upGetting up or moving more slowly may help
Extreme tiredness, feeling short of breath, palpitations, fast heartbeatLet your doctor know straightaway
HeadacheAsk your doctor or pharmacist to recommend a suitable painkiller
Feeling sickStick to simple foods - avoid rich or spicy meals
Feeling shaky or restless, unusual or uncontrollable muscle movementsSpeak with your doctor as soon as possible about any of these. Your treatment may need adjusting
Increased weight, dry mouth, lack of appetite, increased amounts of saliva, feeling hot or sweaty, problems passing urineDiscuss these with your doctor if any become troublesome
Changes to blood tests and ECG testsYour doctor will regularly check for these

Important: if you experience symptoms such as muscle stiffness, a very high temperature, feeling confused, a fast heartbeat and sweating, you should contact your doctor immediately. These can be signs of a rare but serious condition known as neuroleptic malignant syndrome.

If you experience any other symptoms which you think may be due to the medicine, speak with your doctor or pharmacist for further advice.

  • Keep all medicines out of the reach and sight of children.
  • Store in a cool, dry place, away from direct heat and light.

Never take more than the prescribed dose. If you suspect that you or someone else might have taken an overdose of this medicine, go to the accident and emergency department of your local hospital. Take the container with you, even if it is empty.

This medicine is for you. Never give it to other people even if their condition appears to be the same as yours.

Do not keep out-of-date or unwanted medicines. Take them to your local pharmacy which will dispose of them for you.

If you have any questions about this medicine ask your pharmacist.

Further reading & references

Disclaimer: This article is for information only and should not be used for the diagnosis or treatment of medical conditions. EMIS has used all reasonable care in compiling the information but make no warranty as to its accuracy. Consult a doctor or other health care professional for diagnosis and treatment of medical conditions. For details see our conditions.

Original Author:
Helen Allen
Current Version:
Peer Reviewer:
Dr John Cox
Document ID:
3699 (v23)
Last Checked:
16/06/2014
Next Review:
15/06/2017
The Information Standard - certified member

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