Is There a Link Between TSH Levels and Schizophrenia? A Systematic Review and Meta-Analysis

Background: Thyroid dysfunction and psychiatric disorders often coexist, raising interest in their potential interplay. In particular, the relationship between thyroid-stimulating hormone (TSH) levels and schizophrenia has been investigated, though findings remain inconsistent. We performed a systematic review and meta-analysis to clarify whether TSH levels differ in patients with schizophrenia compared with healthy controls. Methods: A systematic search of PubMed/MEDLINE, Scopus, and Web of Science was conducted up to May 2025. Eligible studies were selected based on predefined criteria according to the PICO framework: What are the TSH levels in first-episode, drug-naïve patients diagnosed with schizophrenia compared with healthy subjects, and do TSH levels influence different psychiatric phenotypes? PRISMA guidelines were followed. Study quality and risk of bias were assessed using QUADAS-2. Results: Of 2068 records screened, 35 studies met the inclusion criteria. Quality assessment revealed a generally unclear risk of bias, with few studies showing a high risk. The meta-analysis included 3669 patients and 1391 controls from ten Asian, eight European, and three North American studies. TSH levels were similar between patients and controls (SMD = -0.059 mIU/L; 95% CI: -0.260 to 0.141), with substantial heterogeneity (I² = 84%, p < 0.001). Conclusions: This meta-analysis found no significant association between TSH levels and schizophrenia, despite decades of research and methodological diversity.