BDNF and depressive symptom measurement: A randomized clinical trial compared plasma BDNF in patients with treatment-resistant depression receiving intravenous ketamine (N = 15) versus midazolam (N = 7) and found that ketamine responders had increased BDNF levels peaking at 240 min post-infusion compared to non-responders, while no association between BDNF was found in controls receiving midazolam [20].