The primary objective of this study is to determine if NAC, added to existing antipsychotic treatment, is superior to placebo for cortical erosion in patients with early stage psychosis. The primary hypothesis is that there will be significantly less cortical erosion as measured by cortical thickness, cortical volume and cortical white matter density (assessed by DTI) in patients treated for 12 months with NAC as compared to those treated with placebo. The secondary objectives of this study are to determine if 12 months of NAC add-on treatment is superior to placebo for fMRI determined working memory and semantic memory tasks, cortical MR spectroscopy measures (glutathione, N-acetylaspartate, and glutamine/glutamate levels), electrophysiologically determined attention measures (e.g., mismatch negativity, P300), symptoms, functional measures and cognitive functioning.