Additionally, a correlation analysis between HAMD scores and BDNF levels in MDD patients revealed a prominent negative correlation (P < 0.001, R2 = 0.8127), as illustrated in Fig. 2E. Intriguingly, drug-treated MDD patients with lower HAMD scores displayed significantly higher BDNF levels in their serum exosomes compared to those with higher HAMD scores, as shown in Fig. 2F. This suggests that BDNF-enriched targeted exosomes may have therapeutic potential for MDD. Here, BDNF is linked to major depressive disorder.