Starting Clozapine: The Titration Schedule and the First Weeks

Creator: Ryan S. Sultan, MD
Published: 2026-11-12

By Ryan S. Sultan, MD
Psychiatrist · Columbia University Irving Medical Center
Published November 12, 2026 · 6-minute read

The Clozaril label starts clozapine at 12.5 mg once or twice daily. If that's tolerated, the total daily dose goes up by 25 mg to 50 mg per day toward a target of 300 mg to 450 mg per day, in divided doses, by the end of two weeks.¹ This is the schedule prescribers work from, and the prescriber sets the dose and pace for each patient.

The start is low because clozapine can cause orthostatic hypotension, a slow heart rate, and fainting. The label states that these reactions can occur with the first dose, at doses as low as 12.5 mg, and that the risk is highest during the initial titration, particularly with rapid dose escalation.¹

The titration schedule in the label

Clozapine titration in the US prescribing information
Step	What the label states
Starting dose	12.5 mg once or twice daily
Increases in the first two weeks	25 mg to 50 mg per day in total daily dose, if well tolerated
Target by the end of two weeks	300 mg to 450 mg per day, given as 150 mg to 225 mg twice daily
Later increases	Up to 100 mg, once or twice weekly
Maximum	900 mg per day, given as 450 mg twice daily

Source: Clozaril prescribing information, sections 2.2 and 5.2, revised June 2025.¹ This is the schedule prescribers work from. The dose and pace for a given patient are the prescriber's decision.

The label tells prescribers to consider reducing the dose if hypotension occurs.¹ After a gap in treatment the dose is stepped back down, which is covered on the page about missed clozapine doses.

Tests before the first dose

The label calls for these before clozapine is started:¹

A baseline absolute neutrophil count, the start of the blood test schedule
A physical examination, a medical history, and a review of other medications
Serum potassium and magnesium
A lipid evaluation, which the label recommends at baseline and periodically
Fasting blood glucose for patients with risk factors for diabetes
An ECG and a serum chemistry panel, which the label says to consider

The label's text mentions neither C-reactive protein (CRP) nor troponin.¹ The international guideline adds CRP testing.³ Cardiac monitoring is laid out on the clozapine myocarditis page.

The international guideline is slower and based on ancestry

A 2022 international guideline with 104 authors from 50 countries and regions proposed six titration schedules for adult inpatients. The schedules are grouped by ancestry and by whether clozapine metabolism is expected to be lower, which the guideline ties to obesity, valproate, or oral contraceptives.^{2, 3}

In the first author's summary table, the day 1 dose runs from 6.25 mg to 25 mg per day depending on the group, the day 7 dose from 25 mg to 100 mg, and the day 14 dose from 50 mg to 200 mg. Final targets range from 75 mg to 150 mg per day in the lowest group to 300 mg to 600 mg per day in the highest.³ The label's two-week target is 300 mg to 450 mg per day.¹ As with the label, the prescriber chooses the schedule.

The guideline was written for inpatients, and the author describes the schedules for Black patients as extrapolated from US schedules.³

Does slower titration prevent fever and myocarditis?

Two observational studies associate faster titration with early inflammatory reactions. In an Australian case-control study of 105 myocarditis cases and 296 controls, each additional 250 mg of clozapine given in the first nine days was associated with 26% higher odds of myocarditis (odds ratio 1.26, 95% CI 1.02 to 1.55). Thirty-three of the cases had received less than 920 mg in those nine days, took no valproate, and were under 40.⁴ These are study totals, and the titration pace is set by the prescriber.

In a chart review of Japanese patients at 21 hospitals, with 512 included in the analysis, the outcome was a fever of 37.5°C or higher lasting at least 2 days. The faster titration group had higher odds of fever than the slowest group (adjusted odds ratio 4.05), and the middle group showed no significant difference from the slowest (1.10).⁵

One small study points the other way. In a single-center review of 43 inpatients, most of them White men, the authors concluded that more aggressive titrations did not increase adverse drug reactions.⁶

Can clozapine be started outside the hospital?

The label is silent on the setting.¹ In Danish national registers from 1996 to 2015, 3,262 of 7,932 patients (41.12%) began clozapine as outpatients. One of them (0.03%) developed myocarditis within 2 months, and 26 died within 2 months, with pneumonia and stroke as the main causes of death. The authors estimated the maximum rate of fatal myocarditis at 0.28%.⁷

In a UK service, 65.4% of community initiations were successful, compared with 58.82% of inpatient initiations, a difference that was not statistically significant. That study did not assess safety during the titration period.⁸ A comparison of two monitoring schedules in community initiations, with 16 patients on the lower-frequency schedule, reported no syncope, infection, or deaths in either group, and no clozapine-related side effects requiring hospitalisation.⁹

A PubMed search on November 12, 2026 found no randomized comparison of inpatient and outpatient initiation.

Side effects in the first weeks

The label reports adverse reactions as whole-trial rates, without a week-by-week breakdown. In a 6-week trial of 126 patients on clozapine, sedation was reported in 21%, tachycardia in 17%, constipation in 16%, dizziness in 14%, and hypotension, fever, and hypersalivation in 13% each. Across clozapine studies with 842 patients, the rates were 39% for drowsiness or sedation, 31% for salivation, 19% for dizziness, and 6% for syncope.¹

The label places the peak incidence of clozapine-related fever within the first 3 weeks.¹ Fever, chest pain, or fainting during titration means contacting the prescriber the same day. The side effects page covers the longer term, with separate pages on drooling and constipation.

Limitations of the evidence

This evidence has limitations. First, the studies of titration speed are retrospective, and a PubMed search on November 12, 2026 found no randomized trial comparing a slow titration with a fast one. Second, the outpatient data cited here come from a Danish register and small UK series. Nevertheless, the label and the guideline agree on a low first dose and stepwise increases, and the pace for a given patient is set by the prescriber, who needs to hear about fever, fainting, or chest pain the day it happens.

Frequently asked questions

What is the starting dose of clozapine?

The Clozaril label gives a starting dose of 12.5 mg once or twice daily, because low blood pressure, a slow heart rate, and fainting can occur with the first dose. The prescriber sets the dose and every increase.¹

How long does clozapine titration take?

The label describes reaching a target of 300 mg to 450 mg per day by the end of two weeks if each step is tolerated. A 2022 international guideline for adult inpatients is slower, reaching 50 mg to 200 mg per day at day 14 depending on the group. The prescriber sets the schedule for each patient.^{1, 3}

Can you start clozapine as an outpatient?

The label is silent on the setting. In Danish national registers, 3,262 of 7,932 patients (41.12%) began clozapine as outpatients, and one of them (0.03%) developed myocarditis within 2 months. A PubMed search on November 12, 2026 found no randomized comparison of inpatient and outpatient initiation.^{1, 7}

What blood tests are needed before starting clozapine?

The label calls for a baseline absolute neutrophil count and serum potassium and magnesium, recommends a lipid evaluation, and calls for fasting blood glucose in patients with risk factors for diabetes. It says to consider an ECG and a serum chemistry panel.¹

What side effects are common in the first weeks of clozapine?

In a 6-week trial of 126 patients described in the label, sedation was reported in 21%, tachycardia in 17%, constipation in 16%, dizziness in 14%, and hypotension, fever, and hypersalivation in 13% each. These are whole-trial rates. Fever, chest pain, or fainting during titration means contacting the prescriber the same day.¹

In a crisis: call or text 988, or go to the nearest emergency department. A first episode of psychosis belongs in a hospital-based or coordinated specialty care program.

I start and manage clozapine in an outpatient practice in Chelsea, Manhattan. Details are on the schizophrenia care in NYC page. Clozapine should not be stopped, skipped, or restarted without the prescriber. This page is general information and does not replace an evaluation.