Study to Evaluate Safety & Efficacy of NaBen® as Add-on Treatment for Schizophrenia in Adults

This is an adaptive, phase IIb/III, multi-center, prospective, randomized, placebo-controlled study, in which adult subjects with schizophrenia will be enrolled. The study will include four parts: a 2 week Screening part, a 4 week run-in part, and 8 week double-blind treatment part, and a 52 week Open-Label Extension part. Screening part of the study: The subjects will be evaluated for eligibility during the Screening part of the study. Enrichment run-in part of the study: Subjects who are determined to be eligible will enter the Run-in part of the study. A total of 348 Subjects will be randomized. The randomized subjects will receive 4 weeks of NaBen® or Placebo accordingly. The subjects who have completed 4 weeks of randomized treatment in both groups (NaBen® or Placebo) will be assessed and categorized intoresponders and non-responders, based on 20% or more reduction from baseline in their PANSS total scores as per the evaluations at Visit 2 and Visit 4. Double-Blind treatment part of the study : * Subjects who have successfully completed the Enrichment Run-in part will enter the Double- Blind treatment part of the study per below: NaBen® treated subjects: Subjects will continue receiving NaBen® for another 8 weeks. * Placebo treated subjects: * Placebo Responders: Subjects will continue receiving Placebo for another 8 weeks. * Placebo Non-responders: Subjects will be re-randomized to receive NaBen® or Placebo in a 1:1 ratio for another 8 weeks. Open-Label Extension part of the study: All subjects who have completed the Double-Blind part of the study will continue with the Open-Label Extension part of the study to receive NaBen® for an additional 52 weeks, plus a 2 week follow-up.