Medication Guide
Clozapine (Clozaril) Side Effects and Uses
A plain-language guide to Clozapine, an atypical antipsychotic. Learn how it helps, what it treats, how to take it and which side effects to know about.
Quick answer. Clozapine (Clozaril) is an atypical antipsychotic. Common clozapine side effects include sleepiness, heavy drooling, constipation and weight gain and bigger appetite. The rare but serious ones, and when to get help, are listed under clozapine side effects below. Never stop or change your dose on your own.
How Clozapine Can Help You
Clozapine is the gold standard for treatment-resistant schizophrenia. That means schizophrenia that has not gotten better after at least two other drugs. Clozapine helps many of these people, sometimes a great deal. It is also the only drug of its kind approved to lower suicidal behavior. That use covers schizophrenia and schizoaffective disorder.
The dose is raised slowly for safety. So benefits build over time. Some calm may come within weeks. Fuller gains come over several months. Some people have lived with voices or paranoia for years. For them, clozapine can bring quiet, clear thinking and a chance to rebuild. It also causes fewer movement side effects than most drugs like it.
Uses for Clozapine
- Treatment-resistant schizophrenia
- Lowering suicidal behavior in schizophrenia
- Schizoaffective disorder (off-label)
- Hard-to-treat bipolar disorder (off-label)
- Psychosis in Parkinson's disease (off-label)
- Severe aggression with psychosis (off-label)
How to Take Clozapine
Clozapine is started at a very low dose. It is raised slowly over weeks. Your prescriber decides each step. The slow start guards against low blood pressure, heavy sleepiness and seizures. It is taken once or twice a day, with or without food.
If you miss clozapine for two days or more, do not restart at your usual dose. Call your prescriber first. Your body loses its tolerance fast. The dose often has to be built back up from a low start.
Clozapine needs regular blood tests of your white cells. These are called ANC tests. Tests are more frequent at first and less frequent over time. Your prescriber will also watch weight, blood sugar and cholesterol. They will watch for heart symptoms and constipation too. Report fever, sore throat, chest pain or severe constipation right away.
Clozapine Side Effects
Common Side Effects
- Sleepiness
- Heavy drooling, mostly at night
- Constipation, which must be treated
- Weight gain and bigger appetite
- Dizziness when standing
- Fast heartbeat
- Fever in the first weeks
- Bedwetting at night
- Higher blood sugar or cholesterol
Serious: Get Medical Help Promptly
- Severe neutropenia, a big drop in white cells that fight germs (boxed warning)
- Seizures, more likely at higher doses (boxed warning)
- Myocarditis and cardiomyopathy, which harm the heart muscle (boxed warning)
- Low blood pressure and fainting, mostly at the start (boxed warning)
- Death risk in older adults with dementia and psychosis (boxed warning)
- Severe constipation that can block the bowel
How Clozapine Works
Clozapine acts on many brain receptors at once. It holds dopamine D2 receptors more loosely than most drugs like it. It also acts on serotonin, histamine and other receptors. Experts do not fully know why it helps when others fail. Its broad action is thought to be part of the answer.
Its loose hold on dopamine is why it causes fewer movement side effects. Its effects on histamine and other receptors cause sleepiness, weight gain, drooling and constipation. These side effects are real. But they can often be managed with planning and support.
Before You Start Clozapine
Clozapine takes teamwork. You will need regular blood draws in person. So plan how you will get to a lab. Tell your prescriber about seizures, heart disease, diabetes and bowel problems. Say if you ever had a low white cell count. Share every medicine you take, since some change clozapine levels.
Smoking tobacco lowers clozapine levels. Quitting raises them. So tell your prescriber before you start or stop smoking. Caffeine and some antibiotics can also change levels. Avoid alcohol, which adds to sleepiness and dizziness.
Clozapine can lower suicidal behavior. But warning signs still need care. If you are thinking about harming yourself, call or text 988, or call 911. You can read about schizophrenia care and our crisis resources.
Is Clozapine Right for You?
Only a full evaluation with a prescriber can tell you if Clozapine fits your symptoms, history and goals. Harpal Singh, PMHNP-BC offers psychiatric evaluations and ongoing medication management by telehealth anywhere in California.
SCHEDULE AN APPOINTMENT CALL (888) 457-8124
Related Medication Guides
Other guides in the same group, written the same simple way. Being in one group does not mean you can swap one medicine for another.
- Haloperidol (Haldol), typical (first-generation) antipsychotic
- Lurasidone (Latuda), atypical antipsychotic
- Olanzapine (Zyprexa), atypical antipsychotic
- Paliperidone (Invega), atypical antipsychotic
- Quetiapine (Seroquel), atypical antipsychotic
- Risperidone (Risperdal), atypical antipsychotic
FAQ
Questions About Clozapine
Why does clozapine require so many blood tests?
A small share of people on clozapine develop severe neutropenia, a drop in the white cells that fight infection. Regular ANC tests catch this early, when it can be reversed. Testing is more frequent at first and spaces out as time passes safely.
Is clozapine worth the extra effort?
When schizophrenia has not gotten better with other drugs, clozapine often helps. It is also the only drug of its kind approved to lower suicidal behavior. The monitoring is real work, and many patients and families feel the benefit is worth it.
What symptoms should make me call right away?
Call right away for fever, sore throat or flu-like illness, which can mean low white cells. Also call for chest pain, shortness of breath or a racing heart, severe constipation or belly pain, or a seizure. These are rare but need prompt care, and when in doubt, call.
What happens if I miss my clozapine doses for a couple of days?
If you have missed two days or more, do not restart at your usual dose. Your body loses tolerance quickly, and a full dose could cause dangerous drops in blood pressure or heavy sleepiness. Call your prescriber, who will restart you low and build back up.
How is the drooling managed?
Drooling at night is common and bothersome. A towel on the pillow helps, and your prescriber may suggest other options. It often improves as your body adjusts, so mention it rather than suffering quietly.
Why is constipation such a big deal on clozapine?
Clozapine slows the gut, and severe constipation can lead to a blocked bowel. Drink fluids, stay active and tell your prescriber about fewer bowel movements. Belly pain, swelling or vomiting needs care right away.
Does smoking affect clozapine?
Yes. Tobacco smoke speeds up how fast your body clears clozapine. Quitting can raise levels and side effects, so tell your prescriber before you start or stop smoking.
Can I get clozapine care by telehealth?
Clozapine needs regular blood tests in person at a lab, so it cannot be managed by video alone. Ask your prescriber whether telehealth fits your treatment plan and how lab tests would be arranged.