This is an ascending multiple oral dose, open-label study assessing the safety, tolerability, and pharmacokinetics of SEP-363856 in male and female subjects with schizophrenia. Subjects will have up to two visits, including a screening visit, and a 17-day in-clinic period. Eligible subjects will be admitted to the clinic on Day -4 to start or complete a taper/washout of their prior antipsychotic medication(s) under the supervision of the Investigator. On Day 1, after subjects have successfully completed the taper/washout of prior medication, subjects will be administered SEP 363856, and dosing with SEP 363856 will continue once-daily for 10 days in-clinic dosing. From Day 11 through Day 13, inclusive, subjects will be restabilized on their adequate antipsychotic medication(s) before clinic discharge on Day 14. Some subjects may require a longer restabilization process based on Investigator judgment. Subjects who discontinue the study prior to Day 13 will require an in-clinic stay for 3 days (or longer based on Investigator judgment) for restabilization on prior medications.