Alli is an over-the-counter weight loss supplement that contains orlistat. Orlistat belongs to a class of medications called lipase inhibitors. Lipase inhibitors work in the intestines. They block the fatty foods that you eat from being absorbed in your digestion tract. Instead, the fats pass through your system and never have a chance to turn into added weight on your body. Orlistat is the only ingredient in Alli, which comes in the form of a 60-milligram pill. If you are looking for more orlistat, you are going to have to get a prescription for Xenical, which comes in a 120-milligram dose.