Potent and selective melanocortin MC4 receptor antagonist (Ki values are 3.16, 108, 54.4 and 694 nM for cloned human MC4, MC1, MC3 and MC5 receptors respectively). Increases food intake in rats and nociception in mice following central administration in vivo. Also inhibits IL-1β-induced Fos expression in the paraventricular hypothalamus.