Alli is an over-the-counter weight loss aid containing orlistat, a lipase inhibitor. It works by preventing the absorption of about 25% of the fat you consume. This undigested fat is then eliminated from the body through bowel movements. Alli is intended for overweight adults aged 18 and older who follow a reduced-calorie, low-fat diet.
Because Alli blocks fat absorption, it can also reduce the absorption of fat-soluble vitamins (A, D, E, and K). Taking a multivitamin at bedtime is recommended.
Common side effects, often related to the unabsorbed fat, include oily spotting, gas with discharge, loose stools, and more frequent bowel movements. These effects are generally mild and temporary, and more likely to occur when eating high-fat meals.
Alli is not a quick fix, but rather a tool to support weight loss when combined with diet and exercise.