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.

Eligibility Criteria:
Inclusion Criteria:

* Participant has a diagnosis of schizophrenia (Code 295.90) or schizoaffective disorder (Code 295.70) according to Diagnostic and Statistical Manual of Mental Disorders, 5th edition (DSM 5), based on history and clinical assessment by the investigator
* Participant has current active medication management issues and has experienced a medication treatment modification within the 6 weeks prior to Screening
* Participant is currently taking one or more of the following antipsychotic medications for at least 1 week for oral antipsychotics and at least 1 injection cycle for long-acting injectable (LAI) antipsychotics. In addition, the treating clinician plans to continue the antipsychotic medication(s) for at least 4 weeks subsequent to the Screening visit. Participant may be taking more than one formulation of a particular medication (such as oral and LAI) at or above the minimum dose specified in protocol. Qualifying formulations of the antipsychotic medications are: Aripiprazole (oral formulation only), Olanzapine (oral formulation only), Paliperidone (oral and/or LAI formulations), Quetiapine (oral formulation only), and Risperidone (oral and/or LAI formulations)
* Participant has had no clinically significant suicidal behavior or ideation during the week prior to Screening, according to the investigator's judgment
* Participant is generally healthy and has no clinically significant or unstable medical problems as determined by the investigator, except for the indication for which the antipsychotic treatment is being prescribed. This determination must be recorded in the participant's source documents and initialed by the investigator

Exclusion Criteria:

* Participant has been attending the outpatient psychiatric clinic for more than 12 months since the last psychiatric hospitalization
* During Screening, participant has active alcohol or substance use disorder (except tobacco) of moderate or severe severity according to DSM 5 criteria
* Participant has a history of or currently has a clinically significant (particularly unstable) medical illness, other than the indication for which the participant is taking antipsychotic therapy, that the investigator considers should exclude the participant or that could interfere with the participant completing the study or with interpretation of the study results. Treated, stable, chronic medical problems are allowed, as long as these conditions do not interfere with the study assessments
* Participant is receiving clozapine
* Participant has donated blood or blood products or had substantial loss of blood (ie, blood loss of approximately more than 450 milliliter (mL) or blood loss that required a blood transfusion) within 1 month of Screening or has the intention to donate blood or blood products during the study