IL-4 decreased non-significantly following treatment in schizophrenia (g: −0.84; CI −1.86 to 0.18; p = 0.11; I2 = 97%) whereas in MDD IL-4 increased non-significantly (g: 1.47; CI −0.83 to 3.78; p = 0.210; I2 = 96%). Here, IL4 is linked to major depressive disorder.