Clozapine Side Effects

Medically reviewed by Drugs.com. Last updated on Nov 20, 2023.

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

Important warnings This medicine can cause some serious health issues

Oral route (suspension; tablet; tablet, disintegrating)

Severe Neutropenia. Clozapine 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, Syncope. Orthostatic 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).Seizures. Seizures 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 Incompetence. Fatal 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 Psychosis. Elderly 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 clozapine

Along with its needed effects, clozapine 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

• blurred vision
• confusion
• constipation
• dizziness, faintness, or lightheadedness when getting up suddenly from a lying or sitting position
• fainting
• fast, pounding, or irregular heartbeat or pulse
• fever
• nausea
• 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
• vomiting

Less common

• anxiety
• black, tarry stools
• chest pain or tightness
• chills
• 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 the arms or legs
• painful or difficult urination
• pounding in the ears
• restlessness or need to keep moving
• seizures
• 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
• trouble concentrating
• trouble sleeping
• unsteadiness, trembling, or other problems with muscle control or coordination

Rare

• 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)
• 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
• weakness
• yellow eyes or skin

Incidence not known

• bloating
• burning, crawling, itching, numbness, prickling, "pins and needles", or tingling feelings
• clay-colored stools
• confusion as to time, place, or person
• 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 or skin rash
• 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
• 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

Other side effects of clozapine

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

• 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 ache or pain
• 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, sores, welting, or blisters
• 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
• 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.

General

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

Gastrointestinal

• 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

• 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]

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.

Cholinergic syndrome occurred after abrupt withdrawal.^[Ref]

Metabolic

• 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]

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 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]

Cardiovascular

• 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]

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]

Psychiatric

• 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]

Other

• 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]

Hematologic

• 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]

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]

Genitourinary

• 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]

Dermatologic

• 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]

Ocular

• Common (1% to 10%): Blurred vision, visual disturbances
• Postmarketing reports: Narrow angle glaucoma, periorbital edema^[Ref]

Hepatic

• 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]

Musculoskeletal

• 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]

Respiratory

• 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]

Renal

• Very rare (less than 0.01%): Acute interstitial nephritis/interstitial nephritis
• Postmarketing reports: Renal failure^[Ref]

Hypersensitivity

• Frequency not reported: Angioedema
• Postmarketing reports: hypersensitivity reactions^[Ref]

Endocrine

• Postmarketing reports: Pseudopheochromocytoma^[Ref]

Further information

Clozapine side effects can vary depending on the individual. 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.

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