XENICAL (orlistat) is a lipase inhibitor for obesity management that acts by inhibiting the absorption of dietary fats. Pooled data from clinical trials suggests that people given orlistat in addition to lifestyle modifications, such as diet and exercise, lose about 4.4–6.6 lb more than those not taking the drug over the course of a year.The amount of weight loss achieved with orlistat varies. The primary side effects of the drug are gastrointestinal-related.The manual for Alli makes it clear that orlistat treatment involves aversion therapy, encouraging the user to associate eating fat with unpleasant treatment effects.Absorption of fat soluble vitamins and other fat-soluble nutrients is inhibited by the use of orlistat. A multivitamin tablet containing vitamins A,D,E,K and beta carotene should be taken once a day, at bedtime, when using orlistat.