Study to Determine the Safety, Tolerability, and Efficacy of Evenamide in Patients With Chronic Schizophrenia

Inclusion Criteria: Demographics * Age - 18 years, or older * Sex - male, or non-childbearing potential female unless practicing adequate contraception Psychiatric * Has a current diagnosis of schizophrenia in accordance with DSM-5. * Has been treated with antipsychotics for at least 2 years. * Has a total score on the PANSS \< 80. * Has a Clinical Global Impression - Severity of disease (CGI-S) rating of mildly, moderately or moderately severely ill (score of 3, 4 or 5). * Needs antipsychotic treatment and is currently receiving a stable dose (minimally for 4 weeks prior to screening) of aripiprazole, clozapine, quetiapine, olanzapine, paliperidone, or risperidone (at least 2 mg risperidone dose-equivalent) * Current symptoms have been stably present for at least one month Procedural * Patient resides at home or in a residential care facility * If taking clozapine, patient agrees to blood monitoring Exclusion Criteria: Psychiatric * Severity of current episode of psychosis requires that the patient be hospitalized. Patients who are chronically hospitalized or in psychiatric day-care, whose hospitalization is for logistic reasons and not due to the severity of their illness, will be eligible for the study. * Severity of psychosis is rated severe or higher (CGI-S of 6 or greater). * Known suicidal risk. A "yes" response on the C-SSRS Suicidal Ideation Item 4 or Item 5, or a "yes" response on any of the five C-SSRS Suicidal Behavior items, at screening, or a suicide attempt within the past 6 months, excludes the patient from the study. * Patients with a diagnosis of Treatment resistance * History of neuroleptic malignant syndrome, priapism. * Current moderate or severe tardive dyskinesia. Medical Status * Abnormal epileptiform phenomena (3 per second spike and slow wave discharges) observed on screening EEG. History or current diagnosis of epilepsy or seizure disorder (other than febrile seizures in childhood) * Insulin-dependent diabetes mellitus * History or current diagnosis of any neurodegenerative illnesses * Loss of 500 ml or more of blood during the 3-month period before study enrollment, e.g. as a donor Cardiovascular * A current diagnosis of severe or unstable cardiovascular disease * Any clinically significant ECG abnormality * Abnormal vital signs Laboratory abnormalities * Clinically significant abnormalities in routine laboratory examinations * History and/or presence of hepatitis B and/or C * Positive results from the HIV serology. * Positive results of the drug and alcohol tests * Clinically significant or unstable hypothyroidism or hyperthyroidism Concomitant therapy * Treatment with SSRIs that are moderate/potent inhibitors of CYP2D6 (e.g. fluoxetine) * Treatment with drugs capable of inducing/inhibiting hepatic enzyme metabolism * Current treatment with sodium channel blockers * Exposure to any investigational drug within 5 weeks or 5 half-lives (whichever is longer) prior to screening * A known exaggerated pharmacological sensitivity or hypersensitivity to drugs similar to evenamide (e.g. lamotrigine, carbamazepine, oxcarbazepine, topiramate, etc.), or any components of the evenamide or matching placebo capsules * Treatment with a drug or treatment known to cause major organ system toxicity, e.g. tamoxifen, within 4 weeks, or received radiation therapy or a drug with cytotoxic potential, e.g. chemotherapy, during the past year * Electroconvulsive therapy (ECT) or treatment with a transcranial magnetic stimulation (TMS) device within 6 months prior to screening