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Overview: Clozapine is used to treat schizophrenia and schizoaffective disorder. It is available as an oral liquid, oral tablet, or orally disintegrating tablet. Common side effects include sleepiness, dizziness, headache, tremor, or nausea. Clozapine can affect your alertness or coordination. It can also cause serious side effects, including low blood pressure or fainting, seizures, or a blood disorder that can lead to infections. It is important that you keep all of your appointments, including blood work or other testing, while taking clozapine.

Uses

What is clozapine used for?

Clozapine is commonly used for the following mental health conditions.

Clozapine may also be used for other conditions as determined by your health care provider.

How does clozapine work (mechanism of action)?

Clozapine belongs to a group of medicines called second-generation (atypical) antipsychotics. It is thought to work by balancing brain chemicals called serotonin and dopamine. These chemicals are known to affect thoughts and mood. Clozapine also acts on other receptors in your body.

How is clozapine supplied (dosage forms)?

Brands and other names

  • Clozaril 
  • FazaClo
  • Versacloz

Dosage forms and strengths

  • 50 mg/mL oral suspension
  • 25 mg, 50 mg, 100 mg, 200 mg oral tablets
  • 12.5 mg, 25 mg, 100 mg, 150 mg, 200 mg orally disintegrating tablets

How should I store clozapine?

Oral Tablet. Clozapine oral tablet should be stored at a temperature not to exceed 86 F (30 C). 

Orally Disintegrating Tablet. Clozapine orally disintegrating tablet should be stored at room temperature, between 68 F to 77 F (20 C to 25 C). It can be exposed to temperatures between 59 F to 86 F (15 C to 30 C) for shorter periods of time, such as when transporting it. Store in a cool, dry place. Protect from light and moisture.

Oral Liquid. Clozapine oral liquid should be stored at or below 77 F (25 C). It can be used for up to 100 days after opening the bottle. Store in a cool, dry place. Protect from light. Do not put in the refrigerator or freezer.

Side Effects

What are the most common side effects of clozapine?

The most common side effects of clozapine are listed below. Tell your health care provider if you have any of these side effects that bother you.

  • Drowsiness
  • Dizziness or feeling off balance (vertigo)
  • Headache
  • Tremor
  • Fast heartbeat
  • Low blood pressure or fainting (see below)
  • Excess saliva in your mouth or dry mouth
  • Sweating
  • Vision changes
  • Constipation or nausea
  • Fever (see below)

There may be other side effects of clozapine that are not listed here. Contact your health care provider if you think you are having a side effect of a medicine. In the U.S., you can report side effects to the FDA at www.fda.gov/medwatch or by calling 800-FDA-1088. In Canada, you can report side effects to Health Canada at www.health.gc.ca/medeffect or by calling 866-234-2345.

What are the serious side effects of clozapine?

While less common, the most serious side effects of clozapine are described below, along with what to do if they happen.

Severe Allergic Reactions. Clozapine may cause allergic reactions, including a specific type of allergic reaction called DRESS. DRESS stands for drug reaction with eosinophilia and systemic symptoms. It is also sometimes called multi-organ hypersensitivity. This is a reaction that can affect multiple parts of the body including your liver, kidneys, and heart. Stop taking clozapine and get help right away if you have any of the following symptoms of a serious allergic reaction.

  • Breathing problems or wheezing
  • Racing heart
  • Fever or general ill feeling
  • Swollen lymph nodes
  • Swelling of the face, lips, mouth, tongue, throat, feet, ankles, or legs
  • Shortness of breath, trouble swallowing, or throat tightness
  • Itching, skin rash, or pale red bumps on the skin called hives
  • Nausea or vomiting
  • Dizziness, feeling lightheaded, or fainting
  • Stomach cramps
  • Joint pain
  • Dark-colored pee
  • Your skin or the whites of your eyes turning yellowish in color (also called jaundice)

Severely Low Neutrophil Levels (Severe Neutropenia). Clozapine may cause low levels of a type of white blood cell (called neutrophils), which is known as neutropenia. Neutrophils help prevent infection. Having a low level of neutrophils may increase your risk of serious infections. Tell your health care provider right away if you have any of the following symptoms of low neutrophil levels or an infection. You may need to have blood work right away if you have any of these symptoms.

  • Fever, chills, or sweats
  • Feeling very tired or weak
  • Sore throat, cough, or shortness of breath
  • Sores in your mouth, throat, skin, or rectum
  • Swollen lymph nodes
  • Burning or pain when you pee
  • Unusual vaginal itching or discharge

Metabolism Changes. Clozapine can cause high blood sugar levels or diabetes, high cholesterol levels, and weight gain. Keep all appointments with your health care provider to check your blood work and weight. Call your health care provider if you gain weight or develop the following symptoms of high blood sugar.

  • Thirsty more than usual
  •  Peeing more than usual
  •  Increase in hunger
  •  Tiredness
  •  Feeling sick to your stomach
  •  Confusion
  •  Fruity-smelling breath

Uncontrolled Movements. Clozapine can cause some people to have movements that they cannot control. This condition, called tardive dyskinesia (TD), can cause jerky movements of the face, tongue, or body. TD can be permanent. Call your health care provider right away if you have any of the following symptoms of TD.

  • Tongue sticking out
  • Lip smacking or puckering
  • Grimacing
  • Rapid eye blinking
  • Jerking or twisting motion of the arms, legs, or trunk

Low Blood Pressure Upon Standing (Orthostatic Hypotension), Slow Heartbeat, and Falls. Clozapine may cause a sudden drop in blood pressure when standing up from a seated or lying position. It can also make your heart beat slower than normal (bradycardia). This could lead to fainting or falling, or could cause the heart to stop beating (cardiac arrest). To help prevent low blood pressure, be careful not to get up too quickly. If you feel dizzy, sit or lie down right away until the dizziness stops, then take your time getting up again. Tell your health care provider right away if you have any of the following symptoms.

  • Dizziness, feeling lightheaded, or fainting upon standing
  • Slow heart rate
  • Blurred vision
  • Confusion
  • Feeling weak

Seizures. Some people who have used clozapine have reported having seizures. There are many different types of seizures and some of them are not easy to recognize. Stop taking clozapine and call your health care provider if you have any of the following signs that a seizure is happening or could happen.

  • Muscle twitching, jerking, spasms, tremors, or other uncontrolled movements
  • Stiffening of your arms and legs
  • Feeling anxious, nervous, confused, or a sense of dread
  • Feeling dizzy or lightheaded
  • Falling or losing consciousness

Decreased Alertness or Coordination. Clozapine can affect your alertness or coordination. Do not drive or do other activities that require alertness or coordination until you know how clozapine affects you.

Neuroleptic Malignant Syndrome (NMS). Antipsychotic medicines, like clozapine, may cause a rare but serious condition called neuroleptic malignant syndrome. NMS can lead to death. Stop taking clozapine and contact your health care provider right away if you have any of the following symptoms.

  • High fever
  • Muscle stiffness or rigidity, where it is hard to move
  • Confusion 
  • Changes in your breathing or heart rate
  • Increased sweating

Heart Rhythm Changes. Clozapine may cause a rare, dangerous heart rhythm problem called QT prolongation and torsade de pointes. It could also cause the heart to stop beating (cardiac arrest) or lead to death. Some people have a higher risk of this, including people who are older, have other people in their family who have had these conditions, have low potassium or magnesium levels, or who take medicines that prolong the QT interval. Tell your health care provider right away if you faint or have changes in your heart rate or rhythm, such as a fast or skipping heartbeat.

Heart Muscle Problems. Clozapine may cause myocarditis, which is when your heart muscle becomes inflamed. It may also cause cardiomyopathy, which is when your heart becomes enlarged, thickened, or stiffened. This can affect how well your heart pumps blood. Stop taking clozapine and get emergency help if you have chest pain, shortness of breath, or trouble breathing.

Slowed Gut Movement. Clozapine may cause slowed movement of your digestive tract. This could lead to severe constipation or other serious problems, such as a fecal impaction, gut blockage, or a tear in your gut (perforation). Tell your health care provider right away if you have any of the following symptoms.

  • Hard or dry stools (poop), trouble pooping, or not pooping as much as usual
  • Nausea or vomiting
  • Stomach pain, bloating, or trouble passing gas

Liver Damage. Liver damage, also called hepatotoxicity, can happen when taking clozapine. Keep all your appointments to have your blood checked. Call your health care provider right away if you have any of the following symptoms of liver damage.

  • Nausea or vomiting
  • Stomach or belly pain
  • Fever
  • Weakness or unusual tiredness
  • Itching
  • Loss of appetite
  • Light-colored poop
  • Dark-colored urine (pee)
  • Your skin or the whites of your eyes turning yellowish in color (also called jaundice)

Fever. Some people taking clozapine have developed a fever. This usually happens within the first three weeks of starting the medicine. The fever typically goes away on its own, but some people may need to stop clozapine. A fever can also be a sign of other serious side effects. Tell your health care provider right away if you develop a fever while taking clozapine.

Blood Clot. Clozapine may cause a blood clot in the lungs (pulmonary embolism) or veins (deep vein thrombosis). Stop taking clozapine and get emergency help if you have any of the following signs of a blood clot. 

  • Chest pain or pressure
  • Trouble breathing
  • Pain, swelling, warmth, or tenderness in your arm or leg
  • Skin turning pale or blue

Warnings & Precautions

Who should not use clozapine?

Allergies to Ingredients. People who are allergic to any of the following should not take clozapine.

  • Clozapine
  • Clozaril
  • Versacloz
  • Any of the ingredients in the specific product dispensed

Your pharmacist can tell you all of the ingredients in the specific clozapine products they stock.

What should I know about clozapine before using it?

Do not take clozapine unless it has been prescribed to you by a health care provider. Take it as prescribed.

Do not share clozapine with other people, even if they have the same condition as you. It may harm them.

Keep clozapine out of the reach of children.

It is important that you keep all of your appointments, including labs or other testing, while taking clozapine.

Do not stop taking clozapine without talking to your health care provider. Stopping clozapine suddenly can cause a worsening of mental health conditions or other symptoms, such as sweating, headache, nausea, vomiting, or diarrhea. If you need to stop taking clozapine, your health care provider will give you instructions on how to stop the medicine.

Clozapine may cause constipation. It is important to stay hydrated and get enough fiber and physical activity to help prevent constipation. See the Serious Side Effects section for more details. 

If you are prescribed clozapine oral liquid, use the dosing syringe that comes with your medicine to measure your dose. A household spoon is not an accurate measuring device and may cause you to take the wrong dose. Shake the bottle for at least 10 seconds before measuring out your dose. Ask your pharmacist how to measure and take your medicine properly. 

If you are prescribed clozapine orally disintegrating tablets, do not remove the tablet from its blister pack or bottle until you are ready to take it. You should peel back the foil to open the blister pack. Do not push the tablet through the foil because doing so could damage the tablet. Place the tablet on your tongue and let it melt (no water is needed). The tablet can be allowed to dissolve, or it may be chewed. 

People who are 65 or older can be at greater risk for some side effects from clozapine. Talk to your health care provider about your risks if you are in this age group.

What should I tell my health care provider before using clozapine?

Tell your health care provider about all of your health conditions and any prescription or over-the-counter (OTC) medicines, vitamins/minerals, herbal products, and other supplements you are using. This will help them determine if clozapine is right for you.

In particular, make sure that you discuss any of the following.

Current and Past Health Conditions. Tell your health care provider if you have or have had any of the following.

Psychosis Related to Dementia. There is a higher risk of death, stroke, and mini-stroke in older adults who take clozapine or another antipsychotic and have memory loss or psychosis related to dementia. Clozapine is not approved to treat dementia-related psychosis.

Smoking Tobacco. Tell your health care provider if you smoke tobacco. Smoking tobacco while taking clozapine can make the medicine not work as well. Quitting smoking may increase clozapine levels in your body and may increase the risk of side effects. Talk with your health care provider if you plan to quit smoking. 

Phenylketonuria (PKU). Clozapine orally disintegrating tablets contain phenylalanine, which can be dangerous for people with phenylketonuria (PKU). Tell your pharmacist and other health care providers if you have PKU and are prescribed clozapine orally disintegrating tablets.

Other Medicines and Supplements. Clozapine may interact with other medicines and supplements. Before taking clozapine, tell your health care provider about any prescription or over-the-counter (OTC) medicines, vitamins/minerals, herbal products, and other supplements you are using. See the Interactions section for more details.

Pregnancy. Clozapine taken later in pregnancy may lead to an increased risk of certain problems in your newborn.  Tell your health care provider if you are or plan to become pregnant while taking clozapine. Your health care provider will advise you if you should take clozapine while you are pregnant or trying to get pregnant. If you become pregnant while taking clozapine, you can register with the National Pregnancy Registry for Atypical Antipsychotics by calling 866-961-2388 or at womensmentalhealth.org/research/pregnancyregistry. This registry collects safety information about the use of psychiatric medicines during pregnancy.

Breastfeeding. Clozapine passes into breast milk. Tell your health care provider if you are breastfeeding or plan to breastfeed. Your health care provider will advise you if you should stop breastfeeding or stop clozapine.

Interactions

Does clozapine interact with foods or drinks?

Caffeine may interact with clozapine. Talk with your health care provider if you consume caffeine. Your dose of medicine may need to be changed.

You should not drink alcohol while taking clozapine. Drinking alcohol while taking clozapine could increase your risk of sleepiness, dizziness, feeling lightheaded, or fainting upon standing.

Does clozapine interact with other medicines (drug interactions)?

Always tell your health care provider about any prescription or over-the-counter (OTC) medicines, vitamins/minerals, herbal products, and other supplements you are using.

In particular, make sure that you discuss if you are using any of the following before taking clozapine.

  • Any other medicine for mental health conditions
  • Carbamazepine (Carbatrol, Tegretol, and others) or phenytoin (Dilantin, Phenytek, and others), which is a medicine commonly used to treat seizures or nerve pain
  • Rifampin (Rifadin), which is a medicine commonly used to treat an infection called tuberculosis
  • Any medicine that can cause QT prolongation, which is a potentially dangerous heart rhythm problem, such as amiodarone, chlorpromazine, erythromycin, iloperidone, moxifloxacin, pimozide, quinidine, sotalol, tacrolimus, thioridazine, ziprasidone, and others
  • St. John’s wort, which is a supplement that may be used for depression
  • A medicine for high blood pressure
  • A diuretic, also called a water pill, which is a medicine used to reduce edema (fluid retention) and blood pressure
  • A birth control medicine
  • An antibiotic, which is a medicine to treat infections
  • An anticholinergic medicine, which includes antihistamines and medicines commonly used for overactive bladder, Parkinson’s disease, or stomach problems
  • Any product that contains caffeine, which is often found in medicines for reducing water weight (diuretics), staying awake, headaches, and hangover relief
  • Cimetidine (Tagamet HB), which is a medicine used for heartburn
  • Chemotherapy, which is used to treat certain cancers
  • Any other medicine that causes dizziness and sleepiness, such as prescription pain medicines, sleep medicines, and medicines for anxiety

Many other medicines may alter the blood levels of clozapine, and vice versa. Tell your health care provider about all medicines that you take or have recently taken.

This is not a complete list of medicines that can interact with clozapine. Always check with your health care provider.

Does interact with other drugs you are taking?

Enter your medication into the WebMD interaction checker

Overdose/Missed Dose

What should I do if I accidentally use too much clozapine?

If you or someone else has used too much clozapine, get medical help right away, call 911, or contact a Poison Control center at 800-222-1222.

What should I do if I miss a dose of clozapine?

If you miss a dose, take it as soon as you remember. If it has been more than two days since your last dose, contact your health care provider for advice. You may need to take a different dose. Do not take double or extra doses.