The trade name for an inhibitor of the pancreatic enzyme LIPASE, which breaks down fats in food to their constituent parts. By inhibiting lipase, the drug reduces the amount of dietary fat absorbed from the INTESTINE. It is sometimes prescribed in conjunction with a low-calorie diet and an exercise programme in people with a BODY MASS INDEX of 30 kg/m2 or more (or 28 if they have other risk factors such as DIABETES INSIPIDUS, DIABETES MELLITUS or HYPERTENSION). Orlistat may cause oily, liquid faeces, urgency to defecate, excessive wind and, sometimes, headaches, tiredness and anxiety. (See OBESITY.)