Similarly, BDNF levels remained decreased with a large effect size in individuals in depression irrespective of them being drug-free (g = −1.24, 95 % CI −1.88 to −0.61, P = 0.001, 3 between-group comparisons, n = 257) or on psychiatric medication (g = −0.90, 95 % CI −1.59 to −0.55, P = 0.001, 13 between-group comparisons, n = 839; Table 1, Fig. 1b). Here, BDNF is linked to major depressive disorder.