Clozaril (clozapine)

Clozaril (clozapine)

Brand name: Clozaril®.
Active ingredient name: Clozapine.
Type of medication: Atypical antipsychotic.
Available in Canada from: HLS Therapeutics Inc.
Form: Oral tablets.
Generic: Yes: AA-Clozapine (AA Pharma Inc.); Gen-Clozapine (Mylan Pharmaceuticals ULC).
Listed on Ontario formulary: No – Special Drugs Program; off-formulary interchangeable.
OHIP+ coverage: No – Special Drugs Program.

What is Clozaril used for?

Clozaril is most often used to treat the symptoms of treatment-resistant schizophrenia in adults over 18 years old. Treatment-resistant schizophrenia is diagnosed in individuals who do not respond to or experience serious side effects with at least 2 other antipsychotic medications. In these individuals Clozaril is considered to be more effective at improving symptoms. Clozaril can also be used to treat other mental illnesses. Talk to your doctor to understand why you are taking Clozaril.

How should I take Clozaril?

  • You can take Clozaril with or without food. It can be taken once daily, usually in the evening as it can make people very sleepy. In people who take doses greater than 500 mg per day, the dose is often split into twice daily dosing to decrease the risk of having a seizure.
  • Clozaril is available in 25 mg and 100 mg tablets. The usual dose is 300 mg - 450 mg per day. Most people start with half of a 25 mg tablet once or twice on the first day. Your doctor will gradually increase the dose until your ideal dose is established, to a maximum of 900 mg per day. In some cases, doses can go above 900 mg per day. If your dose is higher than 900 mg discuss the reasons with your doctor.

What are the most common side effects seen with Clozaril? 

The most common side effects of Clozaril include:

  • Drowsiness

  • Increased heart rate

  • Constipation

  • Weight gain

  • Drooling (mostly at night)

Other Side Effects that may occur with Clozaril:

  • Wetting the bed (nocturnal enuresis)
  • Orthostatic hypotension

What are rare but potentially serious side effects seen with Clozaril?

  • Clozaril may cause a potentially life-threatening decrease in white blood cell count. This is important because white blood cells help fight infections and keep us healthy. If your white blood cell count drops too low, you could develop an infection and your body may not be able to fight it off. While you are using Clozaril, you will undergo regular blood tests to ensure your white blood cell levels remain healthy.
  • Clozaril has also been associated with potentially serious heart problems and should not be used in people with a history of heart disease unless discussed with your psychiatrist and a heart doctor. Your doctor will assess your risk and monitor as needed.
  • Clozaril can also reduce the seizure threshold, increasing likelihood of seizures. This is a dose-related side effect; hence the risk is higher at higher doses. In order to minimize the risk, doses larger than 500 mg will be divided into 2 - 3 times per day.
  • Diabetic ketoacidosis (DKA)
  • Neuroleptic malignant syndrome (NMS)


Elderly individuals with dementia-related psychosis treated with antipsychotic medication are at an increased risk of death compared to individuals not receiving antipsychotics. Most deaths appear to be either cardiovascular or infectious. Clozaril is not approved for the treatment of dementia-related psychosis. Some individuals with dementia may, however, be treated with this medication. Discuss the potential risks and benefits of this medication with your doctor for this indication.

What medications interact with Clozaril?

Tell all your doctors, pharmacists and dentist that you are taking Clozaril. You should also tell your doctor or pharmacist if you are taking any other medications, including those obtained without a prescription, and herbal and vitamin products.
The following medications or types of medication may interact with Clozaril:
  • Certain medications for allergies (e.g., Benadryl [diphenhydramine])
  • Certain medications for sleep (e.g., lorazepam, zopiclone)
  • Certain medications for pain (e.g., fentanyl)
  • Certain antibiotics (e.g., ciprofloxacin)
  • Certain anti-convulsants (e.g., carbamazepine)


The following types of medications may interact with Clozaril:

Smoking cigarettes also interacts with Clozaril by decreasing the Clozaril levels in the blood. If you smoke regularly, inform your healthcare provider and indicate approximately how many cigarettes you smoke per day. If you decide to quit and/or reduce the number of cigarettes you smoke, it is important to tell your doctor or pharmacist as your Clozaril dose may need to be adjusted.
Avoid drinking alcohol or using illegal drugs while taking Clozaril.