Xenical is a medicine used to treat obesity. It works in your digestive system to block about one-third of the fat in the food you eat from being digested. Xenical attaches to the enzymes in your digestive system (lipases) and blocks them from breaking down some of the fat you have eaten during your meal. The undigested fat cannot be absorbed and is eliminated by your body. Xenical is indicated in the treatment of obesity in conjunction with a low calorie intake diet.