This study is open to people aged 18 years or older with schizophrenia. People can join the study if they are willing to use a smartphone app called CT-155. This app is being developed to help people with schizophrenia manage their negative symptoms.

The purpose of this study is to gather new information on CT-155. Researchers want to see how well it works, how well participants use the study app, and how it affects the use of health care services.

Participants use the app for 16 weeks. They may continue using it for another 16 weeks. During the study, participants continue with their normal treatment for schizophrenia. Participants are in the study for about a year. During this time, they visit the study site every 2 months.

During this study, doctors regularly check participants' schizophrenia symptoms and overall quality of life. Researchers may also compare the healthcare data of study participants with a similar group of people with schizophrenia who are not part of the study. The doctors also regularly check participants' health and take note of any unwanted effects.

Inclusion Criteria

1. Has a primary diagnosis of schizophrenia using the diagnostic criteria for schizophrenia as defined in the Diagnostic and Statistical Manual of Mental Disorders, Fifth Edition, Text Revision (DSM-5 TR), and/or International Classification of Disease-10 (ICD-10) diagnosis code consistent with a schizophrenia diagnosis.
2. Has a Clinical Global Impression - Schizophrenia (CGI-SCH) negative symptoms score (item #2) ≥ 4 (moderately ill) at Screening.
3. 18 years of age or older at the time of informed consent.
4. Is willing and able to use CT-155 in English language regularly, to provide written informed consent to participate in the study and to be compliant with study-related assessments and activities.
5. Has outpatient treatment status at the time of screening, with no inpatient treatment for schizophrenia within 12 weeks prior to Screening.
6. Is on an antipsychotic medication(s) for at least 12 weeks prior to study entry.
7. Is the sole user of an iPhone with an iPhone operating system (iOS) 16+ or a smartphone with an Android operating system (OS) 12+ with a United States telephone number, and is willing to download and use the specified digital mobile application required by the protocol.
8. Is willing and able to receive SMS text messages and push notifications on their smartphone.

Further inclusion criteria apply.

Exclusion Criteria

1. Has a score of ≥3 (mildly ill) for CGI-SCH positive symptoms (item #1) at Screening.

2. Has active substance use disorder of any severity in the last 3 months, other than caffeine and nicotine. Patients are excluded if they fulfill criteria for moderate or severe substance use disorder for cannabis. Only mild substance use disorder for cannabis is allowed if considered by investigator to not impact ability of the patient to participate in the study.

3. Has suicidal ideation or behavior, as assessed by the Columbia Suicide Severity Rating Scale (C-SSRS):

   • Patients with a "yes" response to either Items #4 or #5 on the C-SSRS Suicidal Ideation Item within the last 3 months (12 weeks) prior to screening, or at Screening.
   • Patients with a "yes" response on the C-SSRS Suicidal Behavior Items within the last 6 months (26 weeks) prior to screening or at Screening.

4. Patients who, in the opinion of the investigator, present a risk of suicide.

5. Is currently enrolled or has participated in the last 3 months (12 weeks) in a mental health related clinical study (interventional or observational).

6. Has participated in previous studies of CT-155 or CT-156.

Once the criteria in section "Time Frame" are fulfilled, researchers can use the 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".

Furthermore, researchers can 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.

One year after the approval has been granted by major Regulatory Authorities and after the primary manuscript has been accepted for publication, or after termination of the development program.

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 the sponsor and/or the independent review panel, including checking that the planned analysis does not compete with sponsor's publication plan); 2. and upon signing of a legal agreement.