Clozaril (Clozapine) Patient Information

Find out why Clozaril is prescribed, side effects of Clozaril, Clozaril warnings, effects of Clozaril during pregnancy, more - in plain English.

Generic name: Clozapine
Brand name: Clozaril

Pronounced: KLOH-zah-ril

Clozaril (clozapine) Full Prescribing Information

Why is Clozaril prescribed?

Clozaril is given to help people with severe schizophrenia who have failed to respond to standard treatments. Clozaril is not a cure, but it can help some people return to more normal lives.

Most important fact about Clozaril

Even though it does not produce some of the disturbing side effects of other antipsychotic medications, Clozaril may cause agranulocytosis, a potentially lethal disorder of the white blood cells. Because of the risk of agranulocytosis, anyone who takes Clozaril is required to have a blood test once a week for the first 6 months. The drug is carefully controlled so that those taking it must get their weekly blood test before receiving the following week's supply of medication. If your blood counts have been acceptable for the 6-month period, you will need to have your blood tested only every other week thereafter. Anyone whose blood test results are abnormal will be taken off Clozaril either temporarily or permanently, depending on the results of an additional 4 weeks of testing.

How should you take Clozaril?

Take e Clozaril exactly as directed by your doctor. Because of the significant risk of serious side effects associated with this drug, your doctor will periodically reassess the need for continued Clozaril therapy. Clozaril is distributed only through the Clozaril Patient Management System, which ensures regular white blood cell testing, monitoring, and pharmacy services prior to delivery of your next supply.

Clozaril may be taken with or without food.


--If you miss a dose...

Take it as soon as you remember. If it is almost time for your next dose, skip the one you missed and go back to your regular schedule. Do not take 2 doses at once.


If you stop taking Clozaril for more than 2 days, do not start taking it again without consulting your physician.

--Storage instructions... .

Store at room temperature.

What side effects may occur when taking Clozaril?

Side effects cannot be anticipated. If any develop or change in intensity, inform your doctor as soon as possible. Only your doctor can determine if it is safe for you to continue taking Clozaril.

The most feared side effect of Clozaril is agranulocytosis, a dangerous drop in the number of a certain kind of white blood cell. Symptoms include fever, lethargy, sore throat, and weakness. If not caught in time, agranulocytosis can be fatal. That is why all people who take Clozaril must have a blood test every week. About 1 percent develop agranulocytosis and must stop taking the drug.

Seizures are another potential side effect, occurring in some 5 percent of people who take Clozaril. The higher the dosage, the greater the risk of seizures.

  • More common side effects of Clozaril may include: Abdominal discomfort, agitation, confusion, constipation, disturbed sleep, dizziness, drowsiness, dry mouth, fainting, fever, headache, heartburn, high blood pressure, inability to sit down, loss or slowness of muscle movement, low blood pressure, nausea, nightmares, rapid heartbeat and other heart conditions, restlessness, rigidity, salivation, sedation, sweating, tremors, vertigo, vision problems, vomiting, weight gain n

  • Less common side effects may include: Anemia, angina (severe, crushing chest pain), anxiety, appetite increase, blocked intestine, blood clots, bloodshot eyes, bluish tinge in the skin, breast pain or discomfort, bronchitis, bruising, chest pain, chills or chills and fever, constant involuntary eye movement, coughing, delusions, depression, diarrhea, difficult or labored breathing, difficulty swallowing, dilated pupils, disorientation, dry throat, ear disorders, ejaculation problems, excessive movement, eyelid disorder, fast, fluttery heartbeat, fatigue, fluid retention, frequent urination, glaucoma (high pressure in the eye), hallucinations, heart problems, hives, hot flashes, impacted stool, impotence, inability to fall asleep or stay asleep, inability to hold urine, inability to urinate, increase or decrease in sex drive, involuntary movement, irritability, itching, jerky movements, joint pain, lack of coordination, laryngitis, lethargy, light-headedness (especially when rising quickly from a seated or lying position), loss of appetite, loss of speech, low body temperature, memory loss, muscle pain or ache, muscle spasm, muscle weakness, nosebleed, numbness, pain in back, neck, or legs, painful menstruation, pallor, paranoia, pneumonia or pneumonia-like symptoms, poor coordination, rapid breathing, rash, runny nose, shakiness, shortness of breath, skin inflammation, redness, scaling, slow heartbeat, slurred speech, sneezing, sore or numb tongue, speech difficulty, stomach pain, stuffy nose, stupor, stuttering, swollen salivary glands, thirst, throat discomfort, tics, twitching, urination problems, vaginal infection, vaginal itch, a vague feeling of being sick, weakness, wheezing, yellow skin and eyes

Why should this drug not be prescribed?

Clozaril is considered a somewhat risky medication because of its potential to cause agranulocytosis and seizures. It should be taken only by people whose condition is serious, and who have not been helped by more traditional antipsychotic medications such as Haldol or Mellaril.

You should not take Clozaril if:

You have a bone marrow disease or disorder;
You have epilepsy that is not controlled;
You ever developed an abnormal white blood cell count while taking Clozaril;
You are currently taking some other drug, such as Tegretol, that could cause a decrease in white blood cell count or a drug that could affect the bone marrow;
You have ever had an allergic reaction to any of its ingredients.

Special warnings about Clozaril

Clozaril can cause drowsiness, especially at the start of treatment. For this reason, and also because of the potential for seizures, you should not drive, swim, climb, or operate dangerous machinery while you are taking this medication, at least in the early stages of treatment.

Even though you will have blood tests weekly for the first 6 months of treatment and every other week after that, you should stay alert for early symptoms of agranulocytosis: weakness, lethargy, fever, sore throat, a general feeling of illness, a flu-like feeling, or ulcers of the lips, mouth, or other mucous membranes. If any such symptoms develop, tell your doctor immediately.

Especially during the first 3 weeks of treatment, you may develop a fever. If you do, notify your doctor.

While taking Clozaril, do not drink alcohol or use drugs of any kind, including over-the-counter medicines, without first checking with your doctor.

If you take Clozaril, you must be monitored especially closely if you have either the eye condition called narrow-angle glaucoma or an enlarged prostate; Clozaril could make these conditions worse.

On rare occasions, Clozaril can cause intestinal problems--constipation, impaction, or blockage--that can, in extreme cases, be fatal.

In very rare cases, Clozaril has been known to cause a potentially fatal inflammation of the heart. This problem is most likely to surface during the first month of treatment, but has also occurred later. Warning signs include unexplained fatigue, shortness of breath, fever, chest pain, and a rapid or pounding heartbeat. If you develop these symptoms, see your doctor immediately. Even a suspicion of heart inflammation warrants discontinuation of Clozaril.

Especially when you begin taking Clozaril, you may be troubled by a dramatic drop in blood pressure whenever you first stand up. This can lead to light-headedness, fainting, or even total collapse and cardiac arrest. Clozaril also tends to increase your heart rate. Both problems are more dangerous for someone with a heart problem. If you suffer from one, make sure the doctor knows about it.

Also, if you have kidney, liver, or lung disease, or a history of seizures or prostate problems, you should discuss these with your doctor before taking Clozaril. Nausea, vomiting, loss of appetite, and a yellow tinge to your skin and eyes are signs of liver trouble; call your doctor immediately if you develop these symptoms.

Drugs such as Clozaril can sometimes cause a set of symptoms called Neuroleptic Malignant Syndrome. Symptoms include high fever, muscle rigidity, irregular pulse or blood pressure, rapid heartbeat, excessive perspiration, and changes in heart rhythm. Your doctor will have you stop taking Clozaril while this condition is being treated.

There is also a risk of developing tardive dyskinesia, a condition of involuntary, slow, rhythmical movements. It happens more often in older adults, especially older women.

Clozaril has been known to occasionally raise blood sugar levels, causing unusual hunger, thirst, and weakness, along with excessive urination. If you develop these symptoms, alert your doctor. You may have to switch to a different medication.

In very rare instances, Clozaril may also cause a blood clot in the lungs. If you develop severe breathing problems or chest pain, call your doctor immediately.

Possible food and drug interactions when taking Clozaril

If Clozaril is taken with certain other drugs, the effects of either could be increased, decreased, or altered. It is especially important to check with your doctor before combining Clozaril with the following:

Antidepressants such as Paxil, Prozac, and Zoloft
Antipsychotic drugs such as Thorazine and Mellaril
Blood pressure medications such as Aldomet and Hytrin
Chemotherapy drugs
Cimetidine (Tagamet)
Digitoxin (Crystodigin)
Digoxin (Lanoxin)
Drugs that depress the central nervous system such as phenobarbital and Seconal
Drugs that contain atropine such as Donnatal and Levsin
Epilepsy drugs such as Tegretol and Dilantin
Epinephrine (EpiPen)
Erythromycin (E-Mycin, Eryc, others)
Fluvoxamine (Luvox)
Heart rhythm stabilizers such as Rythmol, Quinidex, and Tambocor
Rifampin (Rifadin)
Tranquilizers such as Valium and Xanax
Warfarin (Coumadin)

Special information if you are pregnant or breastfeeding

The effects of Clozaril during pregnancy have not been adequately studied. If you are pregnant or plan to become pregnant, inform your doctor immediately. Clozaril treatment should be continued during pregnancy only if absolutely necessary. You should not breastfeed if you are taking Clozaril, since the drug may appear in breast milk.

Recommended dosage for Clozaril


Your doctor will carefully individualize your dosage and monitor your response regularly.

The usual recommended initial dose is half of a 25-milligram tablet (12.5 milligrams) 1 or 2 times daily. Your doctor may increase the dosage in increments of 25 to 50 milligrams a day to achieve a daily dose of 300 to 450 milligrams by the end of 2 weeks. Dosage increases after that will be only once or twice a week and will be no more than 100 milligrams each time. Dosage is increased gradually because rapid increases and higher doses are more likely to cause seizures and changes in heart rhythm. The most you can take is 900 milligrams a day divided into 2 or 3 doses. s.

Your doctor will determine long-term dosage depending upon your response and results of the regular blood tests.


Safety and efficacy have not been established for children up to 16 years of age.


Any medication taken in excess can have serious consequences. If you suspect an overdose of Clozaril, seek emergency medical attention immediately.

  • Symptoms of Clozaril overdose may include: Coma, delirium, drowsiness, excess salivation, low blood pressure, faintness, pneumonia, rapid heartbeat, seizures, shallow breathing or absence of breathing

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Clozaril (clozapine) Full Prescribing Information

back to: Psychiatric Medication Patient Information Index

APA Reference
Staff, H. (2009, January 3). Clozaril (Clozapine) Patient Information, HealthyPlace. Retrieved on 2024, July 18 from

Last Updated: January 24, 2019

Medically reviewed by Harry Croft, MD

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