Xenical (orlistat) was the first drug in a new class of non-systemically acting anti-obesity drugs known as lipase inhibitors.

Orlistat works in your intestines, where it blocks some of the fat you eat from being absorbed and digested. This undigested fat is then removed in your bowel movements.

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.

The effects of orlistat on weight loss, weight maintenance, and weight regain and on a number of obesity-related illnesses were assessed in seven long-term multicenter, clinical trials. These studies included about 2,800 patients treated with orlistat and 1,400 patients treated with a placebo. A well-balanced, reduced- calorie diet was recommended for all patient in the weight-loss and weight-maintenance study periods. The diet was intended to decrease caloric intake by 20 percent and to provide 30 percent of calories from fat. In addition, all patients were offered nutritional counseling.

Of the patients who completed one year of treatment, 57 percent of the patients treated with orlistat and 31 percent of the placebo-treated patients lost at least 5 percent of their baseline body weight.

The recommended dose of orlistat is one capsule with each main meal that includes fat. During treatment, the patient should be on a nutritionally balanced, reduced-calorie diet that contains no more than 30 percent of calories from fat. Orlistat is indicated for obese patients with a body mass index (BMI, a measure of weight in relation to height), of 30 or more, or for patients with a BMI of 27 or more who also have high blood pressure, high cholesterol, or diabetes. A person who is 5’5” in height and weighs 180 pounds would have a BMI of 30.

Because orlistat reduces the absorption of some fat-soluble vitamins and beta carotene, patients should take a supplement that contains fat soluble (A, D, E, and K) vitamins and beta carotene. The most common side effects of orlistat are oily spotting, gas with discharge, fecal urgency, fatty/oily stools and frequent bowel movements.

-- FDA Talk Paper