Clinical Trial of BI 425809 Effect on Cognition and Functional Capacity in Schizophrenia

Inclusion criteria: * Men or women who are 18-50 years (inclusive) of age at time of consent * Established schizophrenia with the following clinical features: * Outpatient, with no hospitalization for worsening of schizophrenia within 3 months prior to randomisation * Medically stable over the prior 4 weeks and psychiatrically stable without symptom exacerbation within 3 months prior to randomisation * patients who have no more than a moderate severe rating on the Positive and Negative Symptom Scale (PANSS) positive items P1, P3-P7 and no more than a moderate rating on the PANSS positive item P2 * Current antipsychotic and concomitant psychotropic medications as assessed at Visit 1 must meet the criteria below: * patients may have up to 2 antipsychotics (typical and/or atypical) * patients must be maintained on current typical and/or atypical antipsychotics other than Clozapine and on current dose for at least 4 weeks prior to randomisation and/or maintained on current long acting injectable antipsychotics and current dose for at least 3 months prior to randomization * patients must be maintained on current concomitant psychotropic medications, anticholinergics, antiepileptics and/or lithium for at least 3 months prior to randomisation and on current dose for at least 4 weeks prior to randomisation * Women of child-bearing potential must be ready and able to use highly effective methods of birth control that result in a low failure rate of less than 1% per year when used consistently and correctly. * Patients must exhibit reliability, physiologic capability, and an educational level sufficient to comply with all protocol procedures, in the investigator´s opinion * Patients must have an identified informant who will be consistent throughout the study. * Further inclusion criteria apply Exclusion criteria: * Patients who have a categorical diagnosis of another current major psychiatric disorder * Diseases of the central nervous system that may impact cognitive test performance * Movement disorder not currently controlled * Patients receiving another investigational drug or procedure within 30 days or 6 half-lives (whichever is longer) or recent participation in another trial with any cognitive enhancing therapy * Recent participation in formal cognitive remediation program * Recent electroconvulsive therapy * Patients who have been on BI 409306, encenicline or other investigational drug testing effects on cognition in schizophrenia within the last 6 months prior to randomisation or who have previously been on bitopertin * Participation in a clinical trial with repeated Measurement and Treatment Research to Improve Cognition in Schizophrenia (MATRICS) Consensus Cognitive Battery (MCCB) assessments within the last 6 months * Patients who required change in ongoing stable benzodiazepine or sleep medication regimen within the last 4 weeks prior to randomisation * Treatment with Clozapine within 6 months prior to randomisation * Treatment with medical devices (e.g. Transcranial Magnetic Stimulation (TMS), neurofeedback) for any psychiatric condition within the last 3 months prior to randomisation * Patients taking strong or moderate Cytochrome P450 (CYPA4) inhibitors or inducers within the last 30 days prior to randomization * Any suicidal behavior in the past 2 years (i.e. actual attempt, interrupted attempt, aborted attempt, or preparatory acts or behavior) prior to randomisation * Any suicidal ideation of type 4 or 5 in the Columbia Suicidal Severity Rating Scale (C-SSRS) in the past 3 months (i.e. active suicidal thought with intent but without specific plan, or active suicidal thought with plan and intent) prior to randomisation * Known history of Human Immunodeficiency Virus (HIV) infection and/or a positive result for ongoing Hepatitis B or C infection on the Visit 1 central lab report * Hemoglobin less than 120 g/L (12g/dL) in men or 115 g/L (11.5 g/dL) in women * History of hemoglobinopathy such as thalassemia major or sickle-cell anemia * Women who are pregnant, nursing, or who plan to become pregnant while in the trial or men who are able to father a child, unwilling to be abstinent or use adequate contraception for the duration of the study participation and for at least 28 days after treatment has ended * Significant history of drug abuse disorder (including alcohol) within the last 6 months prior to informed consent or a positive urine drug screen at screening (except for Benzodiazepines taken according to prescription and as an ongoing, stable regimen) * Further exclusion criteria apply