IL6 and bipolar disorder: IL-6 was found to be increased in mania (SMD 1.07, 95% CI 0.29 to 1.84, P = 0.007, I2 = 93%, k = 6, n = 695) and euthymia (SMD 0.71, 95% CI 0.07 to 1.34, P = 0.03, I2 = 92%, k = 6, n = 734) but not significantly elevated in bipolar depression (SMD 0.67, 95% CI −0.08 to 1.42, P = 0.08, I2 = 91%, k = 6, n = 601) (Fig. 2(b)).