A Study of the Feasibility, Safety and Tolerability of Aticaprant as Adjunctive Treatment 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