Orlistats primary function is preventing the absorption of fats from the human diet by acting as a lipase inhibitor, thereby reducing caloric intake. It is intended for use in conjunction with a healthcare provider-supervised reduced calorie diet.
It is the saturated derivative of lipstatin, a potent natural inhibitor of pancreatic lipases isolated from the bacterium Streptomyces toxytricini. However, due to its relative simplicity and stability, orlistat was chosen over lipstatin for development as an anti obesity drug.
The effectiveness of orlistat in promoting weight loss is definite but modest. Pooled data from clinical trials suggest that people given orlistat in addition to lifestyle modifications, such as diet and exercise, lose about 2 to 3 kilograms (4.4 to 6.6 lb) more than those not taking the drug over the course of a year.
Orlistat also modestly reduces blood pressure and appears to prevent the onset of type 2 diabetes, whether from the weight loss itself or other effects. It reduces the incidence of diabetes type II in people who are obese around the same amount that lifestyle changes do.
