High Quality Content by WIKIPEDIA articles! Orlistat is marketed as a prescription under the trade name Xenical by Roche in most countries, or over-the-counter as Alli by GlaxoSmithKline in the United Kingdom and the United States), also known as tetrahydrolipstatin, is a drug designed to treat obesity. Its primary function is preventing the absorption of fats from the human diet, thereby reducing caloric intake. It is intended for use in conjunction with a physician-supervised reduced-calorie diet. Orlistat is the saturated derivative of lipstatin, a potent natural inhibitor of pancreatic lipases isolated from the bacterium Streptomyces toxytricini. However, due to simplicity and stability, orlistat rather than lipstatin was developed into an anti-obesity drug.