A Study to Compare Disease Progression and Modification Following Treatment With Paliperidone Palmitate Long-Acting Injection or Oral Antipsychotics in Participant's With Recent-onset Schizophrenia or Schizophreniform

The purpose of the study is to compare effectiveness of paliperidone palmitate (PP: paliperidone palmitate once-monthly and 3-month injections) versus oral antipsychotic (OAP \[that is oral paliperidone extended release {ER}, oral risperidone, or another OAP\]) in delaying time to treatment failure. The study will also evaluate changes in cognition, functioning, brain intracortical myelin (ICM) volume following treatment with PP compared with OAP in participants with recent-onset schizophrenia or schizophreniform disorder.

A Prospective, matched-control, Randomized (assignment of study drug by chance), open-label, flexible-dose, study in participants with recent-onset schizophrenia or schizophreniform disorder to compare disease progression and disease modification following treatment with PP long-acting injection (once-monthly followed by 3-month injections) or OAP (Any of the following 7 OAPs are permitted: aripiprazole, haloperidol, olanzapine, paliperidone ER, perphenazine, quetiapine, and risperidone). The study consists of 3 parts. Part-1 (Oral Run-In Phase), Part-2 (Disease Progression) and Part-3 (Extended Disease Progression and Disease Modification) with unique endpoints. Screening period will be up to 4 Weeks. Duration of Parts will be as: 2 months for Part-1, 9 months for Part-2 and Part-3. All participants will initially receive oral paliperidone ER or oral risperidone in Part-1. After paliperidone/risperidone treatment in Part-1, participants will be randomized into 1:2 ratio to receive PP or OAP in Part-2. Participants who complete Part-2 will enter into Part-3 wherein OAP group participants of Part-2 will be re-randomized into 1:1 ratio to OAP-OAP group and OAP-PP group, and PP group will continue without further randomization. Treatment failures will be evaluated in Part-2 and Part-3 of the study. Also changes in cognition, functioning, brain intracortical myelin (ICM) volume will be evaluated in the study. Participants' safety will be monitored throughout. Healthy controls (comparable in age, sex, race, and highest parental education to the treated participants) were recruited at each of the 3 MRI centers as controls for the MRI machine calibration for the duration of the study. These healthy controls were to undergo MRI assessments, but were not otherwise involved with the study and did not receive study medication. No safety or efficacy data were collected for these healthy controls.

Eligibility Criteria:
Inclusion Criteria:

* Participant must have a current diagnosis of schizophrenia (295.90) or schizophreniform disorder (295.40) as defined by Diagnostic and Statistical Manual of Mental Disorders, 5th edition (DSM-5) and confirmed by the Structured Clinical Interview for DSM-5 Disorders (SCID) with a first psychotic episode within the last 24 months prior to the screening visit
* Participant requires treatment with an antipsychotic medication
* Participant must sign an informed consent form (ICF) indicating that he or she understands the purpose of and procedures required for the study and are willing to participate in the study
* Participant must have available a designated individual (example, family member, significant other, friend) who has knowledge of the participant and is generally aware of the participants daily activities, and who agrees to let the study site personnel know of changes in the participants circumstances when the participant is not able to provide this information. The designated individual must sign an informed consent form
* Participant is anticipated to have a stable place of residence for the duration of the trial

Exclusion Criteria:

* Participant has a current DSM-5 diagnosis of dissociative disorder, bipolar disorder, major depressive disorder, schizoaffective disorder, autistic disorder, or intellectual disabilities
* Participant meets the DSM-5 definition of moderate or severe substance use disorder (except for nicotine) within 2 months prior to Screening
* Participant has a history of neuroleptic malignant syndrome
* Participant has received long-acting injectable (LAI) medication within 2 injection cycles prior to the Screening visit
* Participant has mental retardation, defined as pre-morbid intelligence quotient (IQ) as measured by Wechsler Test of Adult Reading at Screening less than (\<) 70