Skip to Content

FazaClo Side Effects

Generic Name: clozapine

Note: This page contains information about the side effects of clozapine. Some of the dosage forms included on this document may not apply to the brand name FazaClo.

Not all side effects for FazaClo may be reported. You should always consult a doctor or healthcare professional for medical advice. Side effects can be reported to the FDA here.

For the Consumer

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

In addition to its needed effects, some unwanted effects may be caused by clozapine (the active ingredient contained in FazaClo). In the event that any of these side effects do occur, they may require medical attention.

You should check with your doctor immediately if any of these side effects occur when taking clozapine:

More common
  • Blurred vision
  • confusion
  • dizziness, faintness, or lightheadedness when getting up suddenly from a lying or sitting position
  • fainting
  • fast, pounding, or irregular heartbeat or pulse
  • fever
  • shakiness in the legs, arms, hands, or feet
  • sleepiness or unusual drowsiness
  • sweating
  • trembling or shaking of the hands or feet
  • unusual tiredness or weakness
Less common
  • Anxiety
  • black, tarry stools
  • chest pain
  • chills
  • convulsions
  • cough or hoarseness
  • decrease in the frequency of urination
  • decrease in urine volume
  • difficult or labored breathing
  • difficulty in passing urine (dribbling)
  • discouragement
  • dry mouth
  • feeling sad or empty
  • fever with or without chills
  • frequent strong or increased urge to urinate
  • general feeling of tiredness or weakness
  • headache
  • hyperventilation
  • irritability
  • lack of appetite
  • loss of bladder control
  • loss of interest or pleasure
  • lower back or side pain
  • muscle spasm or jerking of all extremities
  • painful or difficult urination
  • pounding in the ears
  • restlessness or need to keep moving
  • severe or continuing headache
  • shakiness and unsteady walk
  • slurred speech
  • sore throat
  • sores, ulcers, or white spots on the lips or in the mouth
  • sudden jerky movements of the body
  • sudden loss of consciousness
  • swollen glands
  • throat discomfort
  • tightness in the chest
  • trouble concentrating
  • trouble sleeping
  • unsteadiness, trembling, or other problems with muscle control or coordination
  • Absence of or decrease in movement
  • change in appetite
  • dark urine
  • decreased sexual ability
  • difficult or fast breathing or sudden shortness of breath
  • increased sweating
  • increased thirst
  • increased urination
  • lip smacking or puckering
  • muscle stiffness (severe)
  • nausea
  • puffing of the cheeks
  • rapid or worm-like movements of the tongue
  • swelling or pain in the leg
  • uncontrolled chewing movements
  • uncontrolled movements of the arms and legs
  • unusual bleeding or bruising
  • unusually pale skin
  • vomiting
  • weakness
  • yellow eyes or skin
Incidence not known
  • Abdominal or stomach pain
  • bloating
  • burning, crawling, itching, numbness, prickling, "pins and needles", or tingling feelings
  • clay-colored stools
  • confusion as to time, place, or person
  • constipation
  • diarrhea
  • epileptic seizure that will not stop
  • feeling that others are watching you or controlling your behavior
  • feeling that others can hear your thoughts
  • feeling, seeing, or hearing things that are not there
  • holding false beliefs that cannot be changed by fact
  • inability to move the eyes
  • increased blinking or spasms of the eyelid
  • indigestion
  • itching
  • joint pain
  • light-colored stools
  • muscle twitching
  • pains in the stomach, side, or abdomen, possibly radiating to the back
  • rhythmic movement of the muscles
  • severe mood or mental changes
  • skin rash
  • sticking out of the tongue
  • swelling around the eyes
  • swelling of the body or feet and ankles
  • trouble with speaking
  • unpleasant breath odor
  • unusual behavior
  • unusual excitement, nervousness, or restlessness
  • unusual facial expressions
  • unusual weight gain
  • upper right abdominal or stomach pain
  • vomiting of blood

Some of the side effects that can occur with clozapine may not need medical attention. As your body adjusts to the medicine during treatment these side effects may go away. Your health care professional may also be able to tell you about ways to reduce or prevent some of these side effects. If any of the following side effects continue, are bothersome or if you have any questions about them, check with your health care professional:

More common
  • Acid or sour stomach
  • belching
  • feeling of constant movement of self or surroundings
  • heartburn
  • relaxed and calm sensation of spinning
  • sleepiness
Less common
  • Blurred or loss of vision
  • change or problem with discharge of semen
  • disturbed color perception
  • double vision
  • halos around lights
  • inability to sit still
  • increase in body movements
  • muscle pain or ache
  • muscle weakness
  • night blindness
  • nightmares
  • overbright appearance of lights
  • pain in the back, neck, or legs
  • pain in the chest below the breastbone
  • severe muscle stiffness
  • sore tongue
  • stuffy nose
  • tunnel vision
  • unusual drowsiness, dullness, tiredness, weakness, or feeling of sluggishness
Incidence not known
  • Blistering, peeling, or loosening of the skin
  • hives
  • increased sensitivity of the skin to sunlight
  • painful or prolonged erection of the penis
  • red skin lesions, often with a purple center
  • red, irritated eyes
  • reddening of the skin, especially around the ears
  • severe stomach pain
  • severe sunburn
  • sores, welting, or blisters
  • swelling of the eyes, face, or inside of the nose
  • swelling of the salivary glands

For Healthcare Professionals

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


The most serious adverse reactions include agranulocytosis, seizure, cardiovascular effects, and fever. The most common side effects include drowsiness/sedation, dizziness, tachycardia, constipation, and hypersalivation.[Ref]


Common (1% to 10%): Leukopenia/decreased WBC/neutropenia, leukocytosis
Uncommon (0.1% to 1%): Eosinophilia, agranulocytosis
Rare (less than 0.1%): Anemia
Postmarketing reports: Elevated hemoglobin/hematocrit, increased erythrocyte sedimentation rate, thrombocytosis, thrombocytopenia[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 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]


Very common (10% or more): Weight gain (up to 31%)
Rare (less than 0.1%): Diabetes mellitus, impaired glucose tolerance
Very rare (less than 0.01%): Hyperosmolar coma, ketoacidosis, severe hyperglycemia, hypercholesterolemia, hypertriglyceridemia
Postmarketing reports: Hyperuricemia, hyponatremia, weight loss[Ref]

Pooled data from 8 studies in patients with schizophrenia found the mean change in fasting blood glucose in clozapine 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]

Nervous system

Very common (10% or more): Drowsiness/sedation (39%), dizziness (up to 27%), headache (10%)
Common (1% to 10%): Tremor, syncope, hypokinesia/akinesia, seizures, rigidity, akathisia, vertigo, dysarthria, extrapyramidal symptoms
Frequency not reported: Dystonia, neuroleptic malignant syndrome, tardive dyskinesia
Postmarketing reports: Delirium/abnormal EEG, myoclonus, paresthesia, possible cataplexy, status epilepticus, cholinergic syndrome[Ref]

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; 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.[Ref]


Very common (10% or more): Salivation (31%), hypersalivation (up to 48%), constipation (up to 25%), vomiting (up to 17%), nausea (up to 17%), dyspepsia (up to 14%)
Common (1% to 10%): Dry mouth, abdominal discomfort/heartburn, diarrhea, anorexia
Rare (less than 0.1%): Dysphagia
Very rare (less than 0.01%): Ileus, parotid gland enlargement
Postmarketing reports: Acute pancreatitis, dysphagia, salivary gland swelling, colitis[Ref]


Very common (10% or more): Tachycardia (25%), hypotension (13%), hypertension (12%)
Common (1% to 10%): ECG changes
Rare (less than 0.1%): Circulatory collapse, arrhythmia, myocarditis, pericarditis/pericardial effusion
Very rare (less than 0.01%): Cardiomyopathy, cardiac arrest
Frequency not reported: Deep vein thrombosis
Postmarketing reports: Atrial or ventricular fibrillation, ventricular tachycardia, QT interval prolongation, Torsades de pointes, myocardial infarction, deep vein thrombosis, chest pain/angina pectoris[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.

Collective data gathered from 17 placebo-controlled clinical studies (n=5106) involving the use of atypical antipsychotic agents for the treatment of behavioral disorders in the elderly patient with dementia showed a risk of death 1.6 to 1.7 times greater in the drug-treated patient than in the placebo-treated patient. The average length of duration for the trials was 10 weeks with the cause of death in the majority of cases, though not all, reported as either cardiovascular (e.g., heart failure, sudden death) or infectious (e.g., pneumonia) in nature. Although clozapine was not included in these studies, the consistent findings across all three relevant chemical classes support the opinion that these findings are likely to be applicable to all atypical antipsychotic agents. Clozapine is not indicated for use in the treatment of behavioral disorders in elderly patients with dementia.[Ref]


Common (1% to 10%): Liver enzyme elevations
Postmarketing reports: Cholestasis, hepatitis, jaundice, hepatotoxicity, hepatic steatosis, hepatic necrosis, hepatic fibrosis, hepatic cirrhosis, liver injury (hepatic, cholestatic, and mixed), liver failure, liver transplant[Ref]


Very common (10% or more): Insomnia (up to 20%)
Common (1% to 10%): Disturbed sleep/nightmares, agitation, confusion
Uncommon (0.1% to 1%): Dysphemia
Postmarketing reports: Obsessive compulsive symptoms, post-discontinuation cholinergic rebound adverse reactions[Ref]


Postmarketing reports: Hypersensitivity reactions including photosensitivity, vasculitis, erythema multiforme, skin pigmentation disorder, Stevens-Johnson Syndrome[Ref]


Postmarketing reports: Pseudopheochromocytoma[Ref]


Postmarketing reports: Myasthenic syndrome, rhabdomyolysis, systemic lupus erythematosus, muscle weakness, muscle spasms, muscle pain[Ref]


Postmarketing reports: Sepsis[Ref]


Common (1% to 10%): Visual disturbances
Postmarketing reports: Periorbital edema, narrow-angle glaucoma[Ref]


Very common (10% or more): Fever (13%)
Common (1% to 10%): Fatigue
Postmarketing reports: Creatine phosphokinase elevations[Ref]


Common (1% to 10%): Urinary abnormalities, urinary retention, urinary incontinence
Postmarketing reports: Nocturnal enuresis, priapism[Ref]


Common (1% to 10%): Sweating, rash
Postmarketing reports: Angioedema, leukocytoclastic vasculitis, pigmentation disorder[Ref]


Very rare (less than 0.01%): Respiratory depression or arrest, 1 case of allergic asthma
Frequency not reported: Pulmonary embolism
Postmarketing reports: Aspiration, pleural effusion, pneumonia, lower respiratory tract infection, nasal congestion[Ref]


Postmarketing reports: Acute interstitial nephritis, renal failure[Ref]


1. "Product Information. FazaClo (cloZAPine)." Jazz Pharmaceuticals, Palo Alto, CA.

2. "Product Information. Versacloz (cloZAPine)." Jazz Pharmaceuticals, Palo Alto, CA.

3. "Product Information. Clozaril (clozapine)." Novartis Pharmaceuticals, East Hanover, NJ.

4. Cerner Multum, Inc. "Australian Product Information." O 0

5. Cerner Multum, Inc. "UK Summary of Product Characteristics." O 0

Disclaimer: Every effort has been made to ensure that the information provided is accurate, up-to-date and complete, but no guarantee is made to that effect. In addition, the drug information contained herein may be time sensitive and should not be utilized as a reference resource beyond the date hereof. This material does not endorse drugs, diagnose patients, or recommend therapy. This information is a reference resource designed as supplement to, and not a substitute for, the expertise, skill , knowledge, and judgement of healthcare practitioners in patient care. The absence of a warning for a given drug or combination thereof in no way should be construed to indicate safety, effectiveness, or appropriateness for any given patient. does not assume any responsibility for any aspect of healthcare administered with the aid of materials provided. The information contained herein is not intended to cover all possible uses, directions, precautions, warnings, drug interactions, allergic reactions, or adverse effects. If you have questions about the substances you are taking, check with your doctor, nurse, or pharmacist.