Clozaril
In brief
- Clozaril (clozapine) is a prescription-only medicine (POM) in the UK and is supplied only under mandatory blood monitoring.
- Clozapine is used for treatment‑resistant schizophrenia and to reduce recurrent suicidal behaviour in schizophrenia. It is an atypical (second‑generation) antipsychotic that antagonises dopamine D2 and serotonin 5‑HT2A receptors and interacts with multiple other receptors (muscarinic, histaminic H1, adrenergic), which together produce its antipsychotic effects.
- Typical adult initiation is 12.5 mg once or twice on day 1, titrated over 2–3 weeks to a usual maintenance range of 300–450 mg/day in divided doses; the maximum recommended dose is 900 mg/day. Elderly patients and those with hepatic/renal impairment require lower starting doses and slower titration.
- Administration is oral: standard tablets (25 mg, 50 mg, 100 mg, 200 mg) and oral suspension (50 mg/mL).
- Some effects such as sedation or drowsiness can appear within hours; meaningful antipsychotic symptom improvement typically begins over 1–2 weeks, with full therapeutic effects often taking several weeks (commonly up to 4–6 weeks).
- Clozapine is usually given once or twice daily and provides around 24‑hour symptomatic coverage with daily dosing; the elimination half‑life is variable (commonly ~8–12 hours at steady state), so steady state is reached after several days.
- Do not drink alcohol while taking clozapine — alcohol increases sedation, respiratory depression and orthostatic hypotension and can worsen CNS depression and other adverse effects.
- The most common side effect is drowsiness/sedation; other frequent effects include sialorrhoea (excess saliva), constipation, tachycardia, orthostatic hypotension, weight gain and dizziness. Serious risks include neutropenia/agranulocytosis (mandatory blood monitoring), seizures and myocarditis.
Basic Clozaril information
- INN (international nonproprietary name): Clozapine.
- Brand names available in the United Kingdom: Clozaril; generic clozapine
- ATC code: N05AH02
- Forms and dosages: tablets 25 mg and 100 mg (Clozaril); other clozapine brands are also available as tablets (25 mg, 50 mg, 100 mg, 200 mg) and oral suspension (50 mg/mL)
- Manufacturers in the United Kingdom: Sandoz (Novartis); generic manufacturers such as Mylan and Teva
- Registration status in the United Kingdom: licensed in the UK; supplied only through a mandatory blood-monitoring system
- OTC / Rx classification: Prescription-only medicine (POM)
Clozapine and blood monitoring
Clozapine sits apart from other antipsychotics because many people describe life‑changing symptom control alongside a demanding monitoring schedule.
Blood monitoring is mandatory: in the UK it is weekly for the first 18 weeks, then every two weeks up to one year and monthly thereafter.
A recent white cell or ANC result is needed before each supply, so a missing result can delay dispensing.
Common troublesome side effects include sedation and sialorrhoea, and these can reduce quality of life if not addressed early.
Product snapshot
Core product identifiers
Clozapine is listed by INN as clozapine and is known in the UK under the brand Clozaril.
The ATC code for clozapine is N05AH02, and the medicine is prescription only (POM).
Supply is controlled because of the need for mandatory haematological monitoring.
Forms and strengths
| Dosage form | Strengths | Notes |
|---|---|---|
| Tablets | 25 mg, 50 mg, 100 mg, 200 mg (Clozaril: 25 mg and 100 mg) | Standard oral tablets supplied in blisters or bottles. |
| Oral suspension | 50 mg/mL | Allows flexible dosing for titration and for people who cannot swallow tablets. |
Brands and packaging
Clozaril is the best known brand name in the UK, alongside generic clozapine.
Manufacturers supplying clozapine include Sandoz (Novartis), Mylan and Teva.
Products are supplied in unit‑dose blisters or child‑resistant bottles.
Indications and approved uses in the UK
Licensed clinical indications
What conditions is clozapine approved to treat in the UK?
Clozapine is primarily indicated for treatment‑resistant schizophrenia in adults.
The medicine is also indicated for reducing the risk of recurrent suicidal behaviour in schizophrenia spectrum disorders when appropriate.
Licensed use and prescribing context
- On‑label indications: treatment‑resistant schizophrenia; reduction of recurrent suicidal behaviour in schizophrenia spectrum disorders.
- Legal status: prescription only (POM), with mandatory blood monitoring.
Initiation of clozapine is normally undertaken by secondary care psychiatry teams, with maintenance sometimes moved to shared‑care under GP supervision. Maintenance therapy is chronic and requires regular review.
Typical dosing regimen and titration practicalities
Initiation and titration
How is clozapine started safely?
Initial dosing commonly begins at 12.5 mg once or twice on day one.
Titration proceeds cautiously, typically reaching a maintenance dose of 300–450 mg per day in divided doses over two to three weeks.
The maximum adult dose recorded is 900 mg per day, but most patients remain well controlled on lower maintenance doses.
Titration must be gradual to reduce the risk of adverse events such as orthostatic hypotension and seizures at higher doses.
Practical notes
Report fever, sore throat or signs of infection immediately, because neutropenia may present with non‑specific symptoms.
A dosing calendar and clear instructions for taking divided doses support adherence.
The 50 mg/mL suspension permits fine dose adjustments during titration.
In elderly patients or those with renal or hepatic impairment start lower and titrate more slowly with closer monitoring.
Monitoring: blood tests and safety programmes
Mandatory haematological monitoring
Which blood tests are required and how often?
Clozapine requires mandatory haematological monitoring because of the risk of neutropenia and agranulocytosis.
The standard UK schedule is weekly blood tests for the first 18 weeks, then every two weeks up to one year and monthly thereafter.
Prescribers, the dispensing pharmacy and the patient must be registered with a clozapine monitoring service before supply.
| Time frame | Monitoring requirement |
|---|---|
| Initiation (weeks 0–18) | Weekly full blood count and ANC |
| Up to one year | Every two weeks full blood count and ANC |
| After one year | Monthly full blood count and ANC |
If a count is abnormal, supply is withheld and the prescriber and haematology services are alerted.
Side effects: common, bothersome and severe risks
Common and quality-of-life side effects
Which side effects do patients worry about most with clozapine?
Mild to moderate side effects commonly include drowsiness, sedation and excessive salivation (sialorrhoea).
Other frequent effects are tachycardia, orthostatic hypotension, constipation, weight gain, tremor and blurred vision.
Constipation requires active prevention as it can be serious if neglected.
Discussing strategies such as hydration, dietary fibre and prophylactic laxatives helps address quality‑of‑life concerns and supports adherence.
Serious risks requiring action
| Event | Severity | Immediate action |
|---|---|---|
| Agranulocytosis or neutropenia | Severe | Stop clozapine and refer to prescriber/haematology immediately. |
| Seizures | Serious (dose‑related) | Review dose; seek urgent medical review. |
| Myocarditis or cardiomyopathy | Potentially life‑threatening | Urgent cardiology assessment and stop drug if suspected. |
Seek urgent care for fever, signs of infection, chest pain or unexplained breathlessness.
Proactive constipation management and seizure precautions at higher doses reduce the likelihood of adverse outcomes.
Contraindications and cautionary conditions
Absolute contraindications
Clozapine must not be used in patients with known hypersensitivity to clozapine or excipients.
Severe neutropenia or agranulocytosis is an absolute contraindication unless managed under specialist guidance.
Uncontrolled epilepsy, severe CNS depression or a history of clozapine‑induced myocarditis are other absolute contraindications.
Conditions needing close monitoring
- Liver, renal or significant cardiac disease require close monitoring.
- A history of seizures or epilepsy is a relative contraindication and needs specialist input.
- Prostatic hypertrophy, glaucoma, gastrointestinal obstruction and diabetes are conditions where extra vigilance is needed.
Patients with these conditions need more frequent review, and baseline ECG and liver function tests may be required by the prescriber.
Drug interactions and pharmacology basics
Key interaction mechanisms
Clozapine is predominantly metabolised via CYP1A2, with contributions from CYP3A4 and CYP2D6.
CYP1A2 inhibitors such as fluvoxamine or ciprofloxacin can raise clozapine plasma concentrations and increase toxicity risk.
Conversely, inducers such as carbamazepine or heavy smoking reduce plasma concentrations and may reduce efficacy.
Abrupt smoking cessation commonly increases clozapine levels and can precipitate toxicity if doses are not adjusted.
Practical interaction checks
| Co‑medication | Risk | What to do |
|---|---|---|
| Fluvoxamine, Ciprofloxacin | Increase clozapine levels | Tell the prescriber; therapeutic drug monitoring may be considered. |
| Carbamazepine, Smoking | Decrease clozapine levels | Loss of effect is possible; dose changes should be coordinated with the prescriber. |
| Benzodiazepines, Opioids | Additive sedation and respiratory depression | Be aware of fall risk and respiratory depression. |
Tell the prescriber about any change in smoking and if antibiotics are started.
Special populations: elderly, pregnancy, renal and hepatic impairment
Age and frailty considerations
Elderly patients should start at lower doses, for example 12.5 mg once daily, and titrate slowly.
Older adults are more susceptible to orthostatic hypotension, sedation and risk of falls, so extra monitoring is required.
Fall prevention advice is important.
Pregnancy, renal and hepatic issues
| Population | Recommendation |
|---|---|
| Pregnancy | Use only if benefits justify risks; liaise with obstetrics and psychiatry. |
| Renal impairment | Start at lower doses and monitor more frequently; avoid if severe. |
| Hepatic impairment | Lower initial dose; avoid in severe impairment and monitor liver function. |
Clozapine is not approved for use in children under 18 due to insufficient data.
If clozapine is continued in pregnancy, neonatal monitoring should be planned.
Storage and handling
Store clozapine at room temperature, typically 15–30°C, away from moisture and light.
Keep the medicine in its original packaging and out of reach of children.
Avoid exposure to high humidity, which can affect product integrity.
Missed doses, overdose advice and emergency guidance
Missed dose actions
If a patient misses a dose and it has been less than 48 hours, they should take it as soon as they remember.
They must not double the next dose to make up for missed medication.
If a missed period exceeds 48 hours the guidance is to restart at the initial dose and retitrate under supervision.
Overdose and emergency steps
Signs of overdose include marked sedation, delirium, respiratory depression and possible cardiac arrhythmias.
For severe symptoms call 999 or seek urgent help (NHS 111 for advice).
Urgent care is needed for fever, severe constipation, seizures or chest pain.
Legal status and availability in the UK
Clozaril is a prescription-only medicine (POM) in the UK.
In our online pharmacy, Clozaril is available without a prescription, with discreet delivery to the United Kingdom in 9–21 days.
Counselling points
Key counselling topics include the blood monitoring schedule and the importance of reporting fever or signs of infection immediately.
Common side effects such as sedation and sialorrhoea can be reduced with practical measures, and the effect of smoking on clozapine levels should be remembered.
A dosing chart or calendar, and reminders for blood tests, can support adherence.
Delivery across the United Kingdom
| City | Region | Delivery Time |
|---|---|---|
| London | Greater London | 9–21 days |
| Birmingham | West Midlands | 9–21 days |
| Manchester | Greater Manchester | 9–21 days |
| Leeds | West Yorkshire | 9–21 days |
| Glasgow | Scotland | 9–21 days |
| Edinburgh | Scotland | 9–21 days |
| Bristol | South West England | 9–21 days |
| Newcastle Upon Tyne | North East England | 9–21 days |
| Sheffield | South Yorkshire | 9–21 days |
| Cardiff | Wales | 9–21 days |
| Belfast | Northern Ireland | 9–21 days |
| Southampton | South East England | 9–21 days |
| Norwich | East of England | 9–21 days |
| Plymouth | South West England | 9–21 days |
