Abstract: Treatment with several psychopharmacological agents has been associated with increased leptin plasma concentrations. We measured leptin plasma concentrations in 76 adult depressed patients after a 6-day washout phase and again after 35 days of treatment with amitriptyline or paroxetine, as well as in 73 depressed patients after 28 days of treatment with either mirtazapine or venlafaxine. Leptin plasma concentrations increased during treatment with amitriptyline and mirtazapine, even after controlling for increased body mass index and irrespective of response to treatment [14.5 (13.8) vs 20.3 (18.7) ng/mL, and 12.2 (15.8) vs 14.4 (16.5) ng/mL in the 2 cohorts, respectively]. In contrast, paroxetine and venlafaxine treatment was not associated with changes in leptin plasma concentrations [14.8 (12.0) vs 13.6 (10.6); 15.9 (17.3) vs 13.5 (14.6) ng/mL] nor with weight gain. We conclude that treatment with amitriptyline or mirtazapine is associated with an increase in leptin secretion beyond change in weight. Thus, high leptin levels apparently are ineffective in the control of weight gain, indicating leptin resistance. Leptin resistance may be mediated by an antihistaminergic effect on hypothalamic nuclei integrating signals relevant for energy balance.