Since it's approval by the FDA, Xenical has become the fastest-selling diet medication on the market today — and for good reason.

Years of clinical testing have demonstrated that it is effective. People dieting with Xenical lost an average of 50 percent more weight than those dieting without it. And because Xenical works only in the intestines to block fat absorption by the body, it is unlikely to cause the side effects in other parts of the body that have been reported for some appetite-suppressing drugs that have been withdrawn from the market. But to be most effective, Xenical should be part of a diet-and-exercise program.  

Unlike other obesity drugs, orlistat prevents enzymes in the gastrointestinal tract from breaking down dietary fats into smaller molecules that can be absorbed by the body. Absorption of fat is decreased by about 30 percent. Since undigested triglycerides are not absorbed, the reduced caloric intake may have a positive effect on weight control.