This is a study in adults with schizophrenia. The study tests whether a medicine called BI 425809 together with brain training improves mental abilities.

Participants take study medication once a day for 12 weeks. At the start of the study, the participants are put into 2 groups. It is decided by chance who gets into which group. One group gets BI 425809 tablets every day. The other group gets placebo tablets every day. Placebo tablets look like the BI 425809 tablets, but contain no medicine. During the study, all participants do brain training using a computer.

The doctors regularly test mental abilities of the participants. The results of the mental ability tests are compared between the groups. The doctors also check the general health of the patients.

Inclusion Criteria:

• Signed and dated written informed consent in accordance with ICH Harmonized Tripartite Guideline for Good Clinical Practice (ICH-GCP) and local legislation prior to admission to the trial.

• Male or female patients who are 18-50 years (inclusive) of age at time of consent.

• Established schizophrenia (as per DSM-5) with the following clinical features:

  • Outpatient, with no hospitalization for worsening of schizophrenia within 3 months prior to randomization
  • Psychiatrically stable without symptom exacerbation within 3 months prior to randomization
  • PANSS score ≤ 5 on positive items P1, P3-P7 and ≤ 4 on positive item P2 at Visit 1, and confirmed at Visit 2

• Patients must be on stable antipsychotic treatment; also, current antipsychotic medications and concomitant anticholinergics, antiepileptics, lithium and allowed antidepressants must meet the criteria below:

  • Patients must take 1 and may take up to 2 antipsychotics (typical and/or atypical), except for clozapine
  • Patients must be stable on current antipsychotics, anticholinergics, antiepileptics, lithium and allowed antidepressants for at least 3 months prior to randomization and be on current dose for at least 30 days prior to randomization o Patients on Long-Acting Injectable (LAI) antipsychotics should be on the same medication and dose for at least 3 months prior to randomization

• Women of childbearing potential (WOCBP)2 must be ready and able to use highly effective methods of birth control per Non-Clinical Safety Studies for the Conduct of Human Clinical Trials and Marketing Authorization for Pharmaceuticals (ICH M3 (R2)) that result in a low failure rate of less than 1% per year when used consistently and correctly. A list of contraception methods meeting these criteria is provided in Section 4.2.2.3. Such methods should be used throughout the trial, and for a period of at least 35 days after last trial drug intake, and the patient must agree to periodic pregnancy testing during participation in the trial.

• Patients must demonstrate their ability to properly use the CCT device and program, as well as be compliant with CCT run-in (defined as completing at least 2 hours per week for two weeks, totalling 4 hours CCT, during the screening period)3.

• Patients must be able to comply with all protocol procedures, in the investigator's opinion.

• Patients must have a study partner who will preferably be consistent throughout the study. It is recommended that the study partner should interact (in-person or telephone) with the subject at least 2 times a week.

Exclusion Criteria:

• Patients who have a categorical diagnosis of another current major psychiatric disorder on the Mini-International Neuropsychiatric Interview (M.I.N.I.).

• Diseases of the central nervous system (CNS) that may impact the assessment of the cognitive tests as per investigator's opinion. A movement disorder due to antipsychotic treatment not currently controlled with anti- EPS treatment or another movement disorder (e.g. Parkinson´s disease).

• Patients with a history of participating in any formal cognitive remediation program for 10 or more training sessions.

• Patients who were treated with any of the following medications within the last 6 months prior to randomization:

  • Bitopertin, BI 409306, encenicline or other investigational drug testing effects on cognition in schizophrenia
  • Clozapine (atypical antipsychotic medication)
  • Sarcosine, cycloserine, serine and glycine
  • Stimulants (e.g. methylphenidate, dextroamphetamine, modafinil)
  • Tricyclic antidepressants

• Patients receiving any other investigational drug (other than a potential cognitive enhancing drug) within 30 days or 6 half-lives (whichever is longer) prior to randomization. For investigational LAI antipsychotics, the last injection must be at least 3 months or two administration cycles (i.e. 6 months if administration is every 3 months) prior to randomization, whichever is longer.

• Patients who have participated in a clinical trial with repeated assessments (i.e. a single assessment is not exclusionary) with the MATRICS Consensus Cognitive Battery (MCCB) within the last 6 months prior to randomization.

• Patients who required a change in ongoing benzodiazepine or sleep medication dose or regimen within the last 30 days prior to randomization.

• Patients with known active infection with SARS-CoV-2 within the last 30 days prior to randomization.

• Other exclusion criteria apply

After the study is completed and the primary manuscript is accepted for publishing, researchers can use this following link https://www.mystudywindow.com/msw/datasharing to request access to the clinical study documents regarding this study, and upon a signed "Document Sharing Agreement".

Also, Researchers can use the following link https://www.mystudywindow.com/msw/datasharing to find information in order to request access to the clinical study data, for this and other listed studies, after the submission of a research proposal and according to the terms outlined in the website.

The data shared are the raw clinical study data sets.

After all regulatory activities are completed in the US and EU for the product and indication, and after the primary manuscript has been accepted for publication.

For study documents - upon signing of a 'Document Sharing Agreement'. For study data - 1. after the submission and approval of the research proposal (checks will be performed by both the independent review panel and the sponsor, including checking that the planned analysis does not compete with sponsor's publication plan); 2. and upon signing of a 'Data Sharing Agreement'.