- History of failure to respond to at least two previous sequential antipsychotic treatments different to clozapine, each attaining a chlorpromazine daily dose of≥ 400 mg for a duration ≥ 6 consecutive weeks.Long-acting antipsychotic treatment will not be allowed during the last trial prior to clozapine in order to avoid residual concentrations or effects.Failure of treatment will be defined by a Clinical Global Impression Severity (CGI-Severity) score of ≥4 and score of ≥4 on 2 Positive and Negative Syndrome Scale (PANSS) positive symptom items. The CGI-Severity or Global Assessment of Functioning (GAF) will be completed retrospectively based on information provided by the participant, participant's psychiatrist, medical chart, or other sources of available collateral information.