Anti-obesity pills. Box and blister pack of Xenical pills used for treating obesity. Each pill contains 120 milligrams of the drug orlistat. This drug blocks the pancreatic enzyme lipase, which breaks down fat ready for digestion. Obesity is classified as a body weight 20% over that desirable for a person's height. It can lead to cardiovascular disease, osteoarthritis and diabetes. The primary treatment is a reduction in food intake, and Xenical should only be used when the patient is already on a diet and losing weight.