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Clozaril Side Effects

Generic name: clozapine

Medically reviewed by Last updated on Nov 20, 2023.

Note: This document contains side effect information about clozapine. Some dosage forms listed on this page may not apply to the brand name Clozaril.

Applies to clozapine: oral suspension, oral tablet, oral tablet disintegrating.


Oral route (Suspension; Tablet; Tablet, Disintegrating)

Severe NeutropeniaClozapine treatment has caused severe neutropenia, defined as an absolute neutrophil count (ANC) less than 500/mcL. Severe neutropenia can lead to serious infection and death. Prior to initiating treatment with clozapine a baseline ANC must be at least 1500/mcL for the general population; and must be at least 1000/mcL for patients with documented Benign Ethnic Neutropenia (BEN). During treatment, patients must have regular ANC monitoring. Advise patients to immediately report symptoms consistent with severe neutropenia or infection (eg, fever, weakness, lethargy, or sore throat).Because of the risk of severe neutropenia, clozapine is available only through a restricted program under a Risk Evaluation Mitigation Strategy (REMS) called the Clozapine REMS Program.Orthostatic Hypotension, Bradycardia, SyncopeOrthostatic hypotension, bradycardia, syncope, and cardiac arrest have occurred with clozapine treatment.The risk is highest during the initial titration period, particularly with rapid dose escalation. These reactions can occur with the first dose, with doses as low as 12.5 mg per day , or when restarting patients who have had even a brief interruption in treatment with clozapine.Initiate treatment at 12.5 mg once or twice daily; titrate slowly; and use divided dosages. Use clozapine cautiously in patients with cardiovascular or cerebrovascular disease or conditions predisposing to hypotension (eg, dehydration, use of antihypertensive medications).SeizuresSeizures have occurred with clozapine treatment. The risk is dose-related. Initiate treatment at 12.5 mg, titrate gradually, and use divided dosing. Use caution when administering clozapine to patients with a history of seizures or other predisposing risk factors for seizure (CNS pathology, medications that lower the seizure threshold, alcohol abuse). Caution patients about engaging in any activity where sudden loss of consciousness could cause serious risk to themselves or others.Myocarditis, Cardiomyopathy and Mitral Valve IncompetenceFatal myocarditis and cardiomyopathy have occurred with clozapine treatment. Discontinue clozapine and obtain a cardiac evaluation upon suspicion of these reactions. Generally, patients with clozapine-related myocarditis or cardiomyopathy should not be rechallenged with clozapine. Consider the possibility of myocarditis or cardiomyopathy if chest pain, tachycardia, palpitations, dyspnea, fever, flulike symptoms, hypotension, or ECG changes occur.Increased Mortality in Elderly Patients with Dementia-Related PsychosisElderly patients with dementia-related psychosis treated with antipsychotic drugs are at an increased risk of death. Clozapine is not approved for use in patients with dementia-related psychosis.

Serious side effects of Clozaril

Along with its needed effects, clozapine (the active ingredient contained in Clozaril) may cause some unwanted effects. Although not all of these side effects may occur, if they do occur they may need medical attention.

Check with your doctor immediately if any of the following side effects occur while taking clozapine:

More common

Less common


Incidence not known

Other side effects of Clozaril

Some side effects of clozapine may occur that usually do not need medical attention. These side effects may go away during treatment as your body adjusts to the medicine. Also, your health care professional may be able to tell you about ways to prevent or reduce some of these side effects.

Check with your health care professional if any of the following side effects continue or are bothersome or if you have any questions about them:

More common

Less common

Incidence not known

For Healthcare Professionals

Applies to clozapine: oral suspension, oral tablet, oral tablet disintegrating.


The most commonly reported side effects included salivary hypersecretion, somnolence, and weight gain.[Ref]


Very common (10% or more): Salivary hypersecretion/hypersalivation (up to 48%), salivation (up to 31%), constipation (up to 25%), nausea (up to 17%), vomiting (up to 17%), dyspepsia (up to 14%)

Common (1% to 10%): Abdominal discomfort/dyspepsia/heartburn, diarrhea, dry mouth

Rare (0.01% to 0.1%): Acute pancreatitis, Dysphagia, ileus impaction, pancreatitis

Very rare (less than 0.01%): Fecal impaction/intestinal obstruction/paralytic ileus, parotid gland enlargement

Frequency not reported: Colitis, swallowing difficulty, tongue protrusion

Postmarketing reports: Intestinal infarction/ischemia/fatal intestinal infarction/ischemia, megacolon/fatal megacolon, salivary gland swelling[Ref]

Nervous system

The cumulative incidence of seizure at 1 year is approximately 5% based on pre-marketing testing. The risk is dose-related.

Extrapyramidal symptoms that occur appear to be milder and less frequent than other antipsychotic drugs. There have been no reports of tardive dyskinesia directly attributable to clozapine (the active ingredient contained in Clozaril) however, the syndrome has been reported in a few patients who were treated with other antipsychotics prior to receiving clozapine. A causal relationship can neither be established nor excluded.

Cholinergic syndrome occurred after abrupt withdrawal.[Ref]

Very common (10% or more): Somnolence (up to 46%), drowsiness/sedation (up to 39%), dizziness (up to 27%), vertigo (up to 19%), headache (up to 10%)

Common (1% to 10%): Akathisia, akinesia, convulsions/myoclonic jerks/seizures, dysarthria, extrapyramidal symptoms, hypokinesia, syncope, tremor

Uncommon (0.1% to 1%): Neuroleptic malignant syndrome

Very rare (less than 0.01%): Tardive dyskinesia

Frequency not reported: Dystonia

Postmarketing reports: Abnormal EEG, cholinergic syndrome, clozapine-induced seizures, EEG changes, motor instability, myasthenic syndrome, myoclonus, paresthesia, pleurothotonus, possible cataplexy, post-discontinuation cholinergic rebound adverse reactions, sensory instability, status epilepticus[Ref]


Diabetes mellitus occurred in patients without a history of hyperglycemia or diabetes mellitus.

Pooled data from 8 studies in patients with schizophrenia found the mean change in fasting blood glucose in clozapine (the active ingredient contained in Clozaril) treated patients was +11 mg/dL; pooled data from 10 studies revealed clozapine treatment was associated a mean increase of 13 mg/dl in total cholesterol; pooled data from 11 studies showed a weight gain of 7% or greater relative to baseline body weight occurred in 35% of patients with a mean weight gain of 3.7 kg.[Ref]

Very common (10% or more): Increased weight/weight gain (up to 31%)

Common (1% to 10%): Anorexia

Rare (0.01% to 0.1%): Aggravated diabetes, diabetes mellitus, hyperosmolar coma, impaired glucose tolerance, ketoacidosis, severe hyperglycemia

Very rare (less than 0.01%): Hypercholesterolemia, hypertriglyceridemia

Frequency not reported: Pseudopheochromocytoma

Postmarketing reports: Hypernatremia, hyperuricemia, obesity, weight loss[Ref]


Isolated cases of cardiac arrhythmias, pericarditis/pericardial effusion, and myocarditis have been reported. Postmarketing, very rare events of ventricular tachycardia, cardiac arrest, and QT prolongation which may be associated with Torsades de pointes have been observed, although there is no conclusive causal relationship to use of this drug.[Ref]

Very common (10% or more): Tachycardia (up to 25%), hypotension (up to 13%), hypertension (up to 12%)

Common (1% to 10%): ECG changes, postural hypotension

Rare (0.01% to 0.1%): Arrhythmias, circulatory collapse, myocarditis, pericardial effusion, pericarditis, thromboembolism, ventricular arrhythmia, ventricular fibrillation, ventricular tachycardia

Very rare (less than 0.01%): Cardiac arrest, cardiomyopathy/clozapine-related cardiomyopathy, QT prolongation, skin reactions, Torsade de pointes

Frequency not reported: Angina pectoris/chest pain, myocardial infarction/fatal myocardial infarction, pigmentation disorder, venous thromboembolism

Postmarketing reports: Atrial fibrillation, deep vein thrombosis, mitral valve incompetence, palpitations[Ref]


Very common (10% or more): Insomnia (up to 20%)

Common (1% to 10%): Agitation, confusion, disturbed sleep/nightmares, restlessness

Uncommon (0.1% to 1%): Dysphemia

Rare (0.01% to 0.1%): Delirium, dream activity intensification

Very rare (less than 0.01%): Obsessive compulsive disorder/symptoms

Frequency not reported: Neonatal drug withdrawal syndrome[Ref]


Very common (10% or more): Fever/hyperthermia (up to 13%)

Common (1% to 10%): Benign hyperthermia, fatigue, temperature regulation disturbance

Very rare (less than 0.01%): Sudden unexplained death

Postmarketing reports: Falls, polyserositis, sepsis[Ref]


During pre-marketing testing, the cumulative incidence of agranulocytosis at one year was reported to be 1.3%. Based on Clozaril National Registry (US patients) data collected up to April 1995, a hematologic risk analysis found the incidence of agranulocytosis rises steeply during the first 2 months, peaks at approximately the third month, and decreases at 6 months of therapy; after 6 months, the incidence decreases further, however, it never reaches zero. Individuals with an initial episode of moderate leukopenia (WBC of at least 2000/mm3 and less than 3000/mm3) are at an increased risk of having a subsequent episode of agranulocytosis.

In the UK, agranulocytosis occurred within the first 18 weeks in approximately 70% of patients who developed the condition.

In clinical trials, eosinophil counts of greater than 700/mm3 occurred in approximately 1% of patients. Eosinophilia has been co-reported with some cases of myocarditis (approximately 14%) and pericarditis/pericardial effusion, although it is unknown whether eosinophilia is a reliable predictor of carditis.[Ref]

Common (1% to 10%): Decreased white blood cells, eosinophilia, leukocytosis, leukopenia, neutropenia

Uncommon (0.1% to 1%): Agranulocytosis

Rare (0.01% to 0.1%): Anemia

Very rare (less than 0.01%): Thrombocythemia, thrombocytopenia

Postmarketing reports: Elevated hematocrit, elevated hemoglobin, granulocytopenia, increased erythrocyte sedimentation rate, mild leukopenia, moderate leukopenia, severe leukopenia, thrombocytosis[Ref]


Common (1% to 10%): Urinary abnormalities, urinary incontinence, urinary retention

Very rare (less than 0.01%): Dysmenorrhea, ejaculation change, impotence, priapism

Postmarketing reports: Nocturnal enuresis, retrograde ejaculation[Ref]


Common (1% to 10%): Rash, sweating/sweating disturbance

Frequency not reported: Leukocytoclastic vasculitis

Postmarketing reports: Erythema multiforme, photosensitivity, skin pigmentation disorder, Stevens-Johnson syndrome[Ref]


Common (1% to 10%): Blurred vision, visual disturbances

Postmarketing reports: Narrow angle glaucoma, periorbital edema[Ref]


Common (1% to 10%): Elevated liver enzymes

Rare (0.01% to 0.1%): Cholestasis, cholestatic jaundice, hepatitis

Very rare (less than 0.01%): Fulminant hepatic necrosis

Postmarketing reports: Cholestatic injury, hepatic cirrhosis, hepatic fibrosis, hepatic injury, hepatic necrosis, hepatic steatosis, hepatotoxicity, jaundice, liver failure, liver transplant, mixed injury[Ref]


Common (1% to 10%): Rigidity

Rare (0.01% to 0.1%): Creatine phosphokinase elevation

Frequency not reported: Muscle pain, muscle spasms, muscle weakness, neck muscle spasm, systemic lupus erythematosus

Postmarketing reports: Rhabdomyolysis[Ref]


Rare (0.01% to 0.1%): Aspiration of ingested food, lower respiratory tract infection/fatal lower respiratory tract infection, pneumonia, pulmonary embolism, respiratory arrest, respiratory depression, respiratory depression/arrest with/without circulatory collapse

Very rare (less than 0.01%): Allergic asthma

Frequency not reported: Difficulty breathing, nasal congestion, throat tightness

Postmarketing reports: Pleural effusion, sleep apnea/sleep apnea syndrome[Ref]

Aspiration of ingested food usually occurred in patients with dysphagia or in acute overdose.[Ref]


Very rare (less than 0.01%): Acute interstitial nephritis/interstitial nephritis

Postmarketing reports: Renal failure[Ref]


Frequency not reported: Angioedema

Postmarketing reports: hypersensitivity reactions[Ref]


Postmarketing reports: Pseudopheochromocytoma[Ref]


1. (2001) "Product Information. Clozaril (clozapine)." Novartis Pharmaceuticals

2. Cerner Multum, Inc. "UK Summary of Product Characteristics."

3. Cerner Multum, Inc. "Australian Product Information."

4. (2015) "Product Information. FazaClo (clozapine)." Jazz Pharmaceuticals

5. (2015) "Product Information. Versacloz (clozapine)." Jazz Pharmaceuticals

Further information

Always consult your healthcare provider to ensure the information displayed on this page applies to your personal circumstances.

Some side effects may not be reported. You may report them to the FDA.