A Study to Assess the Safety, Tolerability, Pharmacodynamics and Pharmacokinetics of ASP6981 in Subjects With Schizophrenia

This study will evaluate ASP6981 in stable participants with schizophrenia on stable doses of up to 2 second generation antipsychotic drugs for at least 2 months prior to screening. Participants will be enrolled and randomized into 1 of 4 treatment sequences: AB, BA, CD, DC. Screening period: After a screening period of up to 29 days prior to study drug administration, eligible participants will be admitted to the clinical unit on day -3. Investigational period: Enrolled participants will be randomized to receive either ASP6981 or Placebo first and then will be crossed over to receive the opposite intervention. The study will consist of two treatment periods of 14 days separated by a washout period of 14 days. Participants will be discharged from the clinical unit on day 15 for the washout period. Washout may be extended up to a maximum of 21 days depending on the participant's availability. Follow up: Participants will return to the clinical unit for an End of Study Visit (ESV) on day 28 of period 2 or, if the participant terminated early from the study, 14 days after the last dose of study drug.