To evaluate the possible effect of suicidal behavior on plasma BDNF concentration in TRD patients, we compared baseline plasma BDNF in patients who tried to attempt suicide (0.53 ng/mL) vs. TRD patients without suicidal attempt (0.30 ng/mL), and plasma BDNF concentration did not differ significantly (U = 77.00; p = 0.185; Mann–Whitney test). Here, BDNF is linked to treatment resistant depression.