A Study to Assess the Clinical Utility of Antipsychotic Medication Levels in Plasma as Determined by Liquid Chromatography-Tandem Mass Spectrometry

The purpose of this study is to determine the number of Medication Treatment Modifications (MTMs) made by the clinician at every visit when antipsychotic medication plasma levels (AMPL) results are available compared to when AMPL results are not available.

This is a naturalistic, open-label (all people know the identity of the intervention), multicenter (when more than one hospital or medical school team work on a medical research study), pilot clinical utility study with a sequential and parallel cohort design in participants with a diagnosis of schizophrenia or schizoaffective disorder. The study consists of up to 3 Phases: Screening Phase (Screening and first assessment visit should preferably take place on the same day), active assessment phase (12 weeks, An optional 12 week extension phase. Participants will be assigned to Cohort 1, or randomized to Cohort 2 or Cohort 3. Participants in cohorts 2 and 3 who are receiving long acting injectable (LAI) formulations of paliperidone and/or risperidone and complete participation in the active assessment phase) will have the option of continuing into the extension phase. The duration of study participation will be approximately 12 weeks. Participants in the optional extension phase will have an additional 12 weeks of study participation. The primary outcome will be measured by the number of Medication Treatment Modifications (MTMs) made by the clinician at every visit. Participants' safety will be monitored throughout the study.