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

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.