Clozapine: what you need to know before and after starting

Clozapine is the most effective medicine for treatment‑resistant schizophrenia, but it comes with special rules. If your doctor suggests clozapine, you’ll need regular blood tests, slow dose changes, and close symptom checks. This page gives clear, practical points so you and your caregiver know what to watch for and how to stay safe.

What to expect when starting clozapine

Your doctor usually starts clozapine low and slow — common first doses are 12.5–25 mg at night. The dose is raised over days to weeks to lower risks like low blood pressure, heavy sedation, and seizures. Many people reach 300–450 mg/day; some need more, but higher doses raise seizure risk. Don’t stop clozapine suddenly. Stopping quickly can cause withdrawal, rebound psychosis, or cholinergic symptoms.

Common side effects you may notice early: drowsiness, extra saliva (hypersalivation), constipation, weight gain, and dizziness. Constipation can be serious — tell your prescriber if you have fewer bowel movements, hard stools, or stomach pain. Also avoid driving until you know how the drug affects your alertness and coordination.

Safety checks, blood tests and drug interactions

Clozapine can rarely cause agranulocytosis — a dangerously low white blood cell count. That’s why blood monitoring is mandatory: baseline CBC with differential and absolute neutrophil count (ANC), then weekly checks for the first 6 months, every 2 weeks from months 7–12, and monthly after 12 months if counts stay stable (this is the standard monitoring schedule in many countries). If you get a fever, sore throat, mouth sores, or unexplained infections, contact your provider immediately and get a blood test.

Watch for myocarditis during the first month: rapid heartbeat, chest pain, shortness of breath, or persistent fever. Some clinics check CRP and troponin in the early weeks if symptoms appear or as part of routine monitoring. Also track weight, fasting glucose, and lipids at baseline and periodically — clozapine commonly causes metabolic changes.

Drug interactions matter. Smoking speeds up clozapine clearance (smoking induction of CYP1A2), so stopping smoking can suddenly raise clozapine levels — your dose may need to be cut. Strong CYP1A2 inhibitors like fluvoxamine and some antibiotics (e.g., ciprofloxacin) can raise levels a lot. Carbamazepine is usually avoided because it lowers levels and can increase blood problem risks. Tell your prescriber about all meds, including over‑the‑counter drugs, herbal supplements, and changes in smoking.

Practical tips: keep a log of blood tests and doses, learn early warning signs of infection or myocarditis, carry a note that you take clozapine (useful in emergencies), and involve a caregiver if possible to spot sedation or constipation early. If you have questions about dosing, side effects, or monitoring schedules, ask your psychiatrist or pharmacist — they can tailor advice to your situation.