What it is: The only over-the-counter weight-loss supplement approved by the U.S. Food and Drug Administration.
How it works: The active ingredient, orlistat, blocks an enzyme that breaks down fat in the gut, preventing about 25 percent of fat calories from being absorbed. So with Alli you can lose 20 to 50 percent more weight than with diet and exercise alone. “Results aren’t dramatic, but it can help,” says Caroline Apovian, M.D., director of the Nutrition and Weight Management Center at Boston University Medical Center.
Good to know: Alli can block the absorption of important fat-soluble vitamins, like vitamins A, D, E, and K, so take those supplements two hours before or after taking Alli.