FazaClo Side Effects Center

Last updated on RxList: 9/21/2022
FazaClo Side Effects Center

What Is FazaClo?

FazaClo (clozapine) is an antipsychotic medication used to treat severe schizophrenia symptoms in people who have not responded to other medications. FazaClo is also used to help reduce the risk of suicidal behavior in people with schizophrenia or similar disorders.

What Are Side Effects of FazaClo?

FazaClo may cause serious side effects including:

  • hives,
  • difficulty breathing,
  • swelling of your face, lips, tongue, or throat,
  • fever,
  • sore throat,
  • burning eyes,
  • skin pain,
  • red or purple skin rash with blistering and peeling,
  • flu-like symptoms,
  • extreme weakness,
  • mouth sores,
  • skin sores,
  • new or worsening cough,
  • trouble breathing,
  • pain or burning when you urinate,
  • vaginal itching or discharge,
  • uncontrolled muscle movements in your face (chewing, lip smacking, frowning, tongue movement, blinking or eye movement),
  • seizure,
  • severe constipation,
  • dry or hard bowel movements,
  • painful gas,
  • nausea,
  • vomiting,
  • stomach pain or bloating,
  • chest pain,
  • fast or pounding heartbeats,
  • fluttering in your chest,
  • slow or irregular heartbeats,
  • shortness of breath,
  • sudden dizziness,
  • loss of appetite,
  • stomach pain (upper right side),
  • tiredness,
  • itching,
  • dark urine,
  • clay-colored stools,
  • yellowing of the skin or eyes (jaundice),
  • very stiff (rigid) muscles,
  • high fever,
  • sweating,
  • confusion,
  • tremors,
  • sudden cough,
  • wheezing,
  • rapid breathing, and
  • coughing up blood

Get medical help right away, if you have any of the symptoms listed above.

The most common side effects of FazaClo include:

  • weight gain,
  • dizziness,
  • tremor,
  • fast heart rate,
  • headache,
  • drowsiness,
  • nausea,
  • constipation,
  • dry mouth,
  • increased salivation,
  • vision problems,
  • fever, and
  • increased sweating

Tell the doctor if you have any side effect that bothers you or that does not go away.

Common side effects of FazaClo include:

  • drooling (especially at night),
  • drowsiness,
  • dizziness,
  • spinning sensation,
  • headache,
  • shaking (tremor),
  • vision problems (e.g., blurred vision),
  • dry mouth, constipation,
  • increased sweating,
  • weight gain, or
  • sleep problems

Many of these side effects (especially drowsiness) lessen as the body gets used to the medication.

Seek medical care or call 911 at once if you have the following serious side effects:

  • Serious eye symptoms such as sudden vision loss, blurred vision, tunnel vision, eye pain or swelling, or seeing halos around lights;
  • Serious heart symptoms such as fast, irregular, or pounding heartbeats; fluttering in your chest; shortness of breath; and sudden dizziness, lightheartedness, or passing out;
  • Severe headache, confusion, slurred speech, arm or leg weakness, trouble walking, loss of coordination, feeling unsteady, very stiff muscles, high fever, profuse sweating, or tremors.

This document does not contain all possible side effects and others may occur. Check with your physician for additional information about side effects.

Dosage for FazaClo

It is recommended that treatment with FazaClo begin with a 12.5 mg dose once or twice daily. The dosing should be continued with daily dosage increments of 25-50 mg/day, if well-tolerated, to achieve a target dose of 300-450 mg/day by the end of 2 weeks.

What Drugs, Substances, or Supplements Interact with FazaClo?

FazaClo may interact with cimetidine, citalopram, lithium, rifampin, blood pressure medications, heart rhythm medications, seizure medicines, antibiotics, atropine, belladonna, clidinium, dicyclomine, scopolamine, or diazepam or similar medicines. Tell your doctor all medications and supplements you use.

FazaClo During Pregnancy and Breastfeeding

During pregnancy, FazaClo should be used only when prescribed. Do not stop taking this medication unless directed by your doctor. Babies born to mothers who have used this drug during the last 3 months of pregnancy may infrequently develop symptoms including muscle stiffness or shakiness, drowsiness, feeding/breathing difficulties, or constant crying. If you notice symptoms in your newborn during their first month, tell the doctor. This medication may pass into breast milk and have undesirable effects on a nursing infant. Breastfeeding is not recommended while taking this drug.

Additional Information

Our FazaClo (clozapine) Side Effects Drug Center provides a comprehensive view of available drug information on the potential side effects when taking this medication.

This is not a complete list of side effects and others may occur. Call your doctor for medical advice about side effects. You may report side effects to FDA at 1-800-FDA-1088.


Schizophrenia: Symptoms, Types, Causes, Treatment See Slideshow
FazaClo Consumer Information

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Get emergency medical help if you have signs of an allergic reaction (hives, difficult breathing, swelling in your face or throat) or a severe skin reaction (fever, sore throat, burning eyes, skin pain, red or purple skin rash with blistering and peeling).

You may get infections more easily, even serious or fatal infections. Call your doctor right away if you have signs of infection such as:

  • fever, flu-like symptoms, extreme weakness;
  • mouth sores, skin sores;
  • new or worsening cough, trouble breathing;
  • pain or burning when you urinate; or
  • vaginal itching or discharge.

Further doses may be delayed until your infection clears up.

High doses or long-term use of clozapine can cause a serious movement disorder that may not be reversible. The longer you use clozapine, the more likely you are to develop this disorder, especially if you are a woman or an older adult.

Clozapine can increase your risk of seizure, especially at high doses. Avoid any activity that could be dangerous if you have a seizure or lose consciousness.

Call your doctor at once if you have:

  • uncontrolled muscle movements in your face (chewing, lip smacking, frowning, tongue movement, blinking or eye movement);
  • a seizure (blackout-out or convulsions);
  • severe constipation;
  • dry or hard bowel movements, or painful gas;
  • nausea, vomiting, stomach pain or bloating;
  • heart problems--chest pain, fast or pounding heartbeats, fluttering in your chest, slow heartbeats, shortness of breath, and sudden dizziness (like you might pass out);
  • liver problems--loss of appetite, stomach pain (upper right side), tiredness, itching, dark urine, clay-colored stools, jaundice (yellowing of the skin or eyes);
  • severe nervous system reaction--very stiff (rigid) muscles, high fever, sweating, confusion, fast or uneven heartbeats, tremors, feeling like you might pass out; or
  • signs of a blood clot in the lung--chest pain, sudden cough, wheezing, rapid breathing, coughing up blood.

Untreated constipation may lead to serious bowel complications, hospitalization, or death. Tell your doctor right away if you are not having bowel movements at least 3 times per week.

Common side effects may include:

  • weight gain;
  • dizziness, tremor;
  • fast heart rate;
  • headache, drowsiness;
  • nausea, constipation;
  • dry mouth, or increased salivation;
  • vision problems; or
  • fever, increased sweating.

This is not a complete list of side effects and others may occur. Call your doctor for medical advice about side effects. You may report side effects to FDA at 1-800-FDA-1088.


Schizophrenia is the most disabling mental illness. See Answer
FazaClo Professional Information


The following adverse reactions are discussed in more detail in other sections of the labeling:

  • Severe Neutropenia [see WARNINGS AND PRECAUTIONS]
  • Orthostatic Hypotension, Bradycardia, and Syncope [see WARNINGS AND PRECAUTIONS]
  • Myocarditis and Cardiomyopathy [see WARNINGS AND PRECAUTIONS]
  • Increased Mortality in Elderly Patients with Dementia-Related Psychosis [see WARNINGS AND PRECAUTIONS]
  • Gastrointestinal Hypomotility with Severe Complications [see WARNINGS AND PRECAUTIONS]
  • Eosinophilia [see WARNINGS AND PRECAUTIONS]
  • QT Interval Prolongation [see WARNINGS AND PRECAUTIONS]
  • Metabolic Changes (Hyperglycemia and Diabetes Mellitus, Dyslipidemia, and Weight Gain) [see WARNINGS AND PRECAUTIONS]
  • Neuroleptic Malignant Syndrome [see WARNINGS AND PRECAUTIONS]
  • Hepatotoxicity [see WARNINGS AND PRECAUTIONS]
  • Pulmonary Embolism [see WARNINGS AND PRECAUTIONS]
  • Anticholinergic Toxicity [see WARNINGS AND PRECAUTIONS]
  • Interference with Cognitive and Motor Performance [see WARNINGS AND PRECAUTIONS]
  • Tardive Dyskinesia [see WARNINGS AND PRECAUTIONS]
  • Patients with Phenylketonuria [see WARNINGS AND PRECAUTIONS]
  • Cerebrovascular Adverse Reactions [see WARNINGS AND PRECAUTIONS]
  • Recurrence of Psychosis and Cholinergic Rebound after Abrupt Discontinuation [see WARNINGS AND PRECAUTIONS]

Clinical Trials Experience

Because clinical trials are conducted under widely varying conditions, adverse reaction rates observed in the clinical trials of a drug cannot be directly compared to rates in the clinical trials of another drug and may not reflect the rates observed in clinical practice.

The most commonly reported adverse reactions (≥5%) across clozapine clinical trials were: CNS reactions, including sedation, dizziness/vertigo, headache, and tremor; cardiovascular reactions, including tachycardia, hypotension, and syncope; autonomic nervous system reactions, including hypersalivation, sweating, dry mouth, and visual disturbances; gastrointestinal reactions, including constipation and nausea; and fever. Table 9 summarizes the most commonly reported adverse reactions (≥5%) in clozapine-treated patients (compared to chlorpromazine-treated patients) in the pivotal, 6-week, controlled trial in treatment-resistant schizophrenia.

Table 9: Common Adverse Reactions (≥5%) in the 6-Week, Randomized, Chlorpromazine - controlled Trial in Treatment-Resistant Schizophrenia

Adverse ReactionClozapine
(N=126) (%)
(N=142) (%)
Fever (hyperthermia)134
Dry mouth520

Table 10 summarizes the adverse reactions reported in clozapine-treated patients at a frequency of 2% or greater across all clozapine studies (excluding the 2-year InterSePT™ Study). These rates are not adjusted for duration of exposure.

Table 10: Adverse Reactions (≥2%) Reported in Clozapine-treated Patients (N=842) across all Clozapine Studies (excluding the 2-year InterSePT™ Study)

Body System
Adverse Reaction
N=842 Percentage of Patients
Central Nervous System
Disturbed Sleep/Nightmares4
Seizures (convulsions)3†
Abdominal Discomfort/Heartburn4
Urinary Abnormalities2
Autonomic Nervous System
Dry Mouth6
Visual Disturbances5
Leukopenia/Decreased WBC/Neutropenia3
Weight Gain4
† Rate based on population of approximately 1700 exposed during premarket clinical evaluation of clozapine.

Table 11 summarizes the most commonly reported adverse reactions (≥10% of the clozapine or olanzapine group) in the InterSePT™ Study. This was an adequate and well-controlled, two-year study evaluating the efficacy of clozapine relative to olanzapine in reducing the risk of suicidal behavior in patients with schizophrenia or schizoaffective disorder. The rates are not adjusted for duration of exposure.

Table 11: Incidence of Adverse Reactions in Patients Treated with Clozapine or Olanzapine in the InterSePT™ Study (≥10% in the clozapine or olanzapine group)

Adverse ReactionsClozapine
N=479 % Reporting
N=477 % Reporting
Salivary hypersecretion48%6%
Weight increased31%56%
Dizziness (excluding vertigo)27%12%


Class Effect

Symptoms of dystonia, prolonged abnormal contractions of muscle groups, may occur in susceptible individuals during the first few days of treatment. Dystonic symptoms include: spasm of the neck muscles, sometimes progressing to tightness of the throat, swallowing difficulty, difficulty breathing, and/or protrusion of the tongue. While these symptoms can occur at low doses, they occur more frequently and with greater severity with high potency and at higher doses of first generation antipsychotic drugs. An elevated risk of acute dystonia is observed in males and younger age groups.

Postmarketing Experience

The following adverse reactions have been identified during post-approval use of clozapine. Because these reactions are reported voluntarily from a population of uncertain size, it is not always possible to reliably estimate their frequency or establish a causal relationship to drug exposure.

Central Nervous System

Delirium, EEG abnormal, myoclonus, paresthesia, possible cataplexy, status epilepticus, obsessive compulsive symptoms, and post-discontinuation cholinergic rebound adverse reactions.

Cardiovascular System

Atrial or ventricular fibrillation, ventricular tachycardia, QT interval prolongation, Torsades de Pointes, myocardial infarction, cardiac arrest, and periorbital edema.

Endocrine System


Gastrointestinal System

Acute pancreatitis, dysphagia, salivary gland swelling, megacolon, intestinal ischemia or infarction.

Hepatobiliary System

Cholestasis, hepatitis, jaundice, hepatotoxicity, hepatic steatosis, hepatic necrosis, hepatic fibrosis, hepatic cirrhosis, liver injury (hepatic, cholestatic, and mixed), and liver failure.

Immune System Disorders

Angioedema, leukocytoclastic vasculitis.

Urogenital System

Acute interstitial nephritis, nocturnal enuresis, priapism, and renal failure.

Skin And Subcutaneous Tissue Disorders

Hypersensitivity reactions: photosensitivity, vasculitis, erythema multiforme, skin pigmentation disorder, and Stevens-Johnson Syndrome.

Musculoskeletal System And Connective Tissue Disorders

Myasthenic syndrome, rhabdomyolysis, and systemic lupus erythematosus.

Respiratory System

Aspiration, pleural effusion, pneumonia, lower respiratory tract infection.

Hemic And Lymphatic System

Mild, moderate, or severe leukopenia, agranulocytosis, granulocytopenia, WBC decreased, deep vein thrombosis, elevated hemoglobin/hematocrit, erythrocyte sedimentation rate (ESR) increased, sepsis, thrombocytosis, and thrombocytopenia.

Vision Disorders

Narrow-angle glaucoma.


Creatine phosphokinase elevation, hyperuricemia, hyponatremia, and weight loss.

Read the entire FDA prescribing information for FazaClo (Clozapine)

© FazaClo Patient Information is supplied by Cerner Multum, Inc. and FazaClo Consumer information is supplied by First Databank, Inc., used under license and subject to their respective copyrights.

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