A Clinical Study that will look at an investigational medication, SEP-363856 (called "study medication") in patients with schizophrenia, and assess wether it affectsbody-weight associated parameters. This study is accepting male and female participants age 18 years to 65 years. This study will be conducted in approximately 6 study sites in the United States. Participation could last up to 13 weeks.

This is a double-blind, randomized, multiple dose study in male and female adult subjects with schizophrenia. Subjects will undergo structural magnetic resonance abdominal imaging (MRI) scans as well as hyperinsulinemic euglycemic clamp (HEC) also known as "glucose clamp", after the check-in and towards the end of the treatment phase. Subjects will be randomized to SEP-363856 or their prior antipsychotic (PA). Subjects randomized to SEP-363856 will undergo blinded wash out of their PA, subsequent SEP-363856 blinded titration and 15 day of well tolerated SEP-363856 exposure. Subjects randomized to their prior antipsychotic (PA), will undergo pseudo PA washout, followed by pseudo-titration and 15 day of well tolerated PA exposure. Subjects will be discharged after subject is stable. All subjects will return to the clinic 7 + 2 days post discharge for follow-up assessments.

Inclusion Criteria: This is not an all inclusive list

• Male or female subjects between 18 and 65 years of age, inclusive at time of consent.
• Subject meets Diagnostic and Statistical Manual of Mental Disorders (DSM-5) criteria for a primary diagnosis of schizophrenia as established by clinical interview, using the DSM-5 as a reference and confirmed using the Structured Clinical Interview for DSM-5, Clinical Trials Version [SCID-CT]).
• Subject must have a Positive and negative symptoms scale (PANSS) total score ≤ 80 at Screening and a score of ≤ 4 on the following PANSS items at Screening: P7 (hostility) and G8 (uncooperativeness)
• Subject must have a Clinical Global Impressions - Severity (CGI-S) score ≤ 4 (normal to moderately ill) at Screening.
• Subject must be receiving risperidone, olanzapine, quetiapine or aripiprazole as treatment for schizophrenia at the time of Screening.

Exclusion Criteria: This is not an all inclusive list

• Subject has a DSM-5 diagnosis or presence of symptoms consistent with a DSM-5 diagnosis other than schizophrenia or intellectual disability (IQ < 70).
• Subject has attempted suicide within 12 months prior to Screening.
• Subject answers "yes" to "Suicidal Ideation" Items 4 (active suicidal ideation with some intent to act, without specific plan) or Item 5 (active suicidal ideation with specific plan and intent) on the C-SSRS at Screening (ie. in the past 1 month) or at any subsequent C-SSRS assessment prior to dosing (ie, since last visit).
• Subject is at risk of harming him/herself or others according to the Investigator's judgment.

Anonymized Individual participant data (IPD) that underlie the results of this study will be shared with researchers to achieve aims pre-specified in a methodologically sound research proposal. Small studies with less than 25 participants are excluded from data sharing.

Data will be available after marketing approval in global markets, or beginning 1-3 years following article publication. There is no end date to the availability of the data.

Otsuka will share data on the Vivli data sharing platform which can be found here: https://vivli.org/ourmember/Otsuka/

Double Blind