HCRT and major depressive disorder: The meta-analysis revealed significantly decreased plasma orexin-A levels in schizophrenia (SMD = -0.38; 95% CI: -0.72 to -0.05; p = 0.03) and increased levels in major depressive disorder (SMD = 0.38; 95% CI: 0.15 to 0.60; p = 0.001) compared to healthy controls.