BDNF and major depressive disorder: Ketamine, an anesthetic with psychedelic proprieties, have been tested in MD patients and animal models (Haile et al., 2014; Lepack et al., 2014; Allen et al., 2015; Ly et al., 2018), and patients with treatment resistant depression exhibited increased plasma BDNF after a ketamine session only in responders between 4 h after intake until 1 week later (Haile et al., 2014; Allen et al., 2015).