The purpose of this study is to see how feasible it is to enroll participants with schizophrenia and for them to complete the study/assessments. It will also assess how safe and tolerable aticaprant is when compared with placebo in participants with schizophrenia.

Inclusion criteria:

• Clinically stable with a diagnosis of schizophrenia confirmed by the mini international neuropsychiatric interview [MINI] for psychotic disorders
• The participant must be on a stable dose of only one atypical antipyschotic medication
• Must be receiving outpatient treatment for schizophrenia from a psychiatric provider at the time of screening
• At the Baseline visit, must have a presence of permitted background antipsychotic medication based on blood samples drawn at the screening visit
• If taking an antidepressant or anxiolytic, no dose changes are allowed to have occurred within 8 weeks prior to screening or throughout the double blind treatment phase

Exclusion criteria:

• Has one or more of the current or prior (lifetime) diagnostic and statistical manual of mental disorders (5th edition) (DSM-5) diagnoses (based on the MINI for psychotic disorders): intellectual disability, schizoaffective disorder, schizophreniform disorder, brief psychotic disorder, delusional disorder, psychotic disorder not otherwise specified (NOS), substance-induced psychotic disorder, bipolar disorder, major depressive disorder (recurrent or current episode)
• Has a history of moderate-to-severe substance use disorder, including alcohol use disorder, according to DSM-5 criteria within 6 months before screening except for nicotine or caffeine (based on the MINI and clinical judgment)
• Current cannabis (marijuana, pot, grass, hash, etcetera) use exceeds 3 to 5 times over the past 30 days as measured by items from the national survey on drug use and health (NSDUH) questionnaire
• Has a history in the past 6 months of a peptic ulcer, or lifetime history of upper gastrointestinal bleeding, or known untreated helicobacter pylori infection, or has a diagnosis of zollinger-ellison syndrome (ZES)
• Has current homicidal ideation/intent, per the investigator's clinical judgment

The data sharing policy of Johnson & Johnson Innovative Medicine is available at www.innovativemedicine.jnj.com/our-innovation/clinical-trials/transparency. As noted on this site, requests for access to the study data can be submitted through Yale Open Data Access (YODA) Project site at yoda.yale.edu