The team tested the drug first on mice, and now on "spontaneously obese" rhesus monkeys. "Spontaneously obese" in this case means the monkeys in question became obese in the old-fashioned way: binge-eating and a lack of exercise. It's a naturally occurring behavior in this species, and it's convenient for testing. Compared with the control group, which saw no change, the rhesus monkeys treated with the drug saw reductions in body weight, body mass index, and even waistline measurements (scientific term: abdominal circumference). It's a big deal that the drug worked on primates as well--many weight-loss drugs fail in the move from rodent testing to primate testing.