This study aims to compare total tau and phosphorylated tau levels in plasma, serum (collectively referred to as peripheral blood), and cerebrospinal fluid (CSF) between individuals with schizophrenia and healthy controls, and to further examine total tau levels in BD.<h4>Methods</h4>Employing a meticulous search strategy across PubMed, Embase, Medline and Web of Science, this study adheres to PRISMA guidelines. Here, MAPT is linked to schizophrenia.