A potent antagonist of NPY receptor Y5 (Kis = 1.3, 0.79, 0.74, and 1.4 nM for human, rhesus monkey, mouse, and rat receptors, respectively); >7,500-fold selective for Y5 over other NPY receptors and lacks activity in a panel of 180 receptors, enzymes, and ion channels at concentrations up to 1 μM; increases intracellular calcium in CHO cells expressing the human Y5 receptor in a concentration-dependent manner; reduces body weight gain in wild-type and diet-induced obese mice when administered at a dose of 30 mg/kg; reduces retroperitoneal fat pad weight, epididymal and mesenteric fat pad weights, leptin levels, and food intake in lean mice fed a high-fat diet