Sounds like 'KLOE-za-peen'

Easy-to-read medicine information about clozapine – what is it, how to take it safely and possible side effects.

Type of medicine Also called
  • Antipsychotic
  • Belongs to a group of medicines known as atypical antipsychotics 
  • Clopine®
  • Clozaril®

What is clozapine?

Clozapine is used to treat schizophrenia. It does not cure schizophrenia, but will help to ease your symptoms and support your recovery. It works by restoring the balance of certain natural chemicals in your brain (neurotransmitters).  Clozapine belongs to a group of medicines called antipsychotics. It is used when people have tried at least 2 other antipsychotic medications and found they did not benefit sufficiently, or for people who are unable to tolerate other antipsychotics because of their side effects. About 1 in every 3 people with schizophrenia fall into these groups. Clozapine is available as tablets or a liquid.    


  • The dose of clozapine is different for different people, depending on your response to the medication. 
  • Your doctor will start you on a low dose and increase it slowly as your body gets used to the medication.  
  • A typical schedule would be 12.5 mg once or twice on day 1, increased to 25 mg once or twice on day 2.
  • Over the following 2 to 3 weeks your dose would be increased gradually by 25 mg to 50 mg a day, until you are taking the dose which your doctor believes will give you the most benefit. This can be up to a maximum of 900 mg per day.
  • Dose increases may vary depending upon your doctor, your response to treatment and your medical history.
  • Always take your clozapine exactly as your doctor has told you. The pharmacy label on your medicine will tell you how much clozapine to take, how often to take it, and any special instructions.

How to take clozapine

  • Clozapine is usually taken twice a day. However, if your total dose is 200 mg or less, your doctor may allow you to take the whole amount in one dose, usually in the evening. Try to take your clozapine dose at the same times each day.
  • You can take clozapine with or without food.
  • Swallow clozapine tablets with a full glass of water or other liquid. Liquid clozapine may be taken alone or in water, if required.
  • Limit or avoid drinking alcohol while you are taking clozapine. Alcohol may increase your chance of side effects such as drowsiness.
  • Smoking affects the way your body breaks down (metabolises) clozapine. If you start smoking, or stop smoking while you are taking clozapine, tell your health care provider. Your dose of clozapine may need to be adjusted. If you wish to stop smoking while you are taking clozapine, your doctor can plan a smoking cessation programme with you and monitor your clozapine levels.  
  • If you forget to take your dose, take it as soon as you remember, if it is within 4 to 6 hours of when it was due. But if it is nearly time for your next dose, just take the next dose at the right time. Do not take double the dose.
  • If you forget to take clozapine for more than 48 hours, you must contact your doctor or the clinic you normally attend. Your dose may need to be adjusted. 
  • Keep taking clozapine every day. It usually takes a few weeks to start working and it can take several months before you feel the full benefits.
  • Do not stop taking clozapine suddenly as your symptoms may return if you stop taking it too early; speak to your doctor or nurse before stopping.


Blood tests

Clozapine can affect your blood cells, mainly a type of white blood cells called neutrophils. These cells are responsible for fighting infection and keeping your immune system healthy.

  • When clozapine causes a small drop in the number of these cells, it leads to a condition called neutropenia. A more severe reduction in your white blood cells is called agranulocytosis. A drop in neutrophils puts you at greater risk of picking up infections.
  • Blood tests are important because a drop in the number of your white blood cells may not cause any symptoms until you develop an infection.
  • Checking the number of  your white blood cells on a regular basis helps to detect any changes early on before they cause problems. You will not be allowed to receive clozapine unless you have an up-to-date blood result.
  • You will need to have a blood test within 10 days before starting clozapine treatment, then every week for the first 18 weeks of treatment. After this time, you will need to have blood tests every 4 weeks throughout treatment.

Other tests

Clozapine may cause changes in your blood sugar level, cholesterol level and heart functioning. To keep an eye out for these effects, your doctor will monitor your physical health. You will have your weight measured regularly. You may be sent for tests to monitor your liver, cholesterol and glucose levels. You may also have your blood pressure measured and be required to undergo an ECG test to assess your heart rate.

Possible side effects

Like all medicines, clozapine can cause side effects, although not everyone gets them. Often side effects improve as your body gets used to the new medicine.


Constipation is a common side effect of clozapine (up to 6 in every 10 people taking clozapine may experience constipation). This can be very uncomfortable and if not treated, it can lead to serious stomach problems.

  • You can prevent constipation by increasing the fluid and fibre intake in your diet, and exercising regularly. Read more about preventing constipation.
  • If you have problems with constipation before starting clozapine, tell your doctor. You can be started on a laxative to prevent constipation.
  • If you develop symptoms of constipation while taking clozapine, it is important to contact your health provider for immediate treatment. These symptoms include not having a bowel movement for 2 days or more, severe tummy pain, bloating, feeling sick (nausea) or being sick (vomiting) and reduced appetite. Diarrhoea (runny poos) is also a symptom of constipation.  
  • You are at increased risk of constipation during the first 4 months of starting clozapine, if you have an increase in your clozapine dose, if you are taking other medicines that are likely to cause constipation and when quitting smoking.          

Flu symptoms

  • Clozapine can affect the production of white blood cells which fight infection. It can put you at greater risk of picking up infections. 
  • At the first sign of infection (such as fever, cold or flu symptoms, muscle aches, headache, or sore throat) you need to contact your doctor or mental health worker for an urgent blood test to check your white blood cells.

Other side effects

Side effects What should I do?
  • Feeling sleepy, drowsy, tired 
  • It can last a few hours after the dose.
  • Do not drive or use tools or machinery.
  • Avoid drinking alcohol.
  • Tell your doctor if troublesome.
  • Feeling shaky and restless (cannot sit still)
  • Eyes or tongue may move on their own
  • It is not dangerous but a well-known side effect.  
  • If it is troublesome, tell your doctor.
  • Increased salivation or drooling
  • You dribble and your mouth gets full of saliva or spit. Your pillow is wet in the morning. 
  • This is not dangerous, but can be upsetting.
  • Your doctor may be able to give you a medicine to help this.
  • Propping up pillows at night helps some people a bit.
  • Weight gain from eating more
  • A diet full of vegetables and fibre may help prevent weight gain.
  • Limit sugary or fatty foods.
  • Speak with your doctor if your weight becomes troublesome.
  • Problems with passing urine such as not being able to have a wee, or passing urine when you don't want to (during the night).    
  • Talk to your doctor or care worker about this. It might be helpful to change the time you take your dose or doses.
  • Sometimes taking another medicine can help.
  • Signs of diabetes such as losing weight, passing lots of urine, and feeling thirsty and hungry all the time. 
  • Tell your doctor if you get these symptoms. You can then have some simple tests to see if you are developing diabetes.
  • Signs of problems with your heart (called myocarditis) such as sudden tiredness, shortness of breath, difficulty breathing, fever, chest pain, or fast heart beat
  • Tell your doctor immediately or ring HealthLine 0800 611 116


When certain medications are taken together, an unintended reaction may occur – this is known as an interaction. Clozapine interacts with a number of important medications and herbal supplements so check with your doctor or pharmacist.

Learn more

The following links provide further information on clozapine. Be aware that websites from other countries may contain information that differs from New Zealand recommendations. 

Clopine Medsafe Consumer Information, NZ
Clozaril Medsafe Consumer Information, NZ
Clozapine Patient Info, UK


  1. Safer prescribing of high-risk medicines: Clozapine. BPAC, July 2014
  2. Clozapine. Malignant constipation can kill Goodfellow Gems
Credits: Sandra Ponen, Pharmacist. Reviewed By: Nicola Rowbottom, Pharmacist, South Canterbury Last reviewed: 19 Jul 2017