Tobacco smoke, not nicotine, induces the liver enzyme CYP1A2, which metabolises clozapine and olanzapine. When a patient stops smoking, including on admission to a smoke-free ward, that induction wears off over one to two weeks and clozapine levels can rise substantially. Sedation, hypersalivation, constipation and, at high levels, seizures can follow.
The reverse also applies: a patient who restarts smoking after discharge may see levels fall and symptoms return. Nicotine replacement does not induce CYP1A2, so it does not prevent the rise.
- Ask about smoking at every clozapine review and record changes.
- Check a clozapine level about a week after a patient stops smoking, and consider a dose reduction guided by it.
- Warn patients and families about drowsiness, drooling and constipation after quitting.
- Recheck the level if the patient restarts smoking after discharge.
Why it matters
Smoke-free admissions quietly raise clozapine levels, and the toxicity is often blamed on something else.
Read the rest in the app
You have read your two free briefings this month. The app carries all 27 specialties, every morning, free — and this finding is waiting in it.
Scan to keep reading on your phone. No account needed to start.
Tomorrow morning, before your first patient
One edition a day for psychiatry, written by the desk, every claim tied to its paper. Six minutes.
Get the app — free