Typically, enzymes in your intestines break down fat from food so your body can absorb the fat. But, the active ingredient in alli attaches to some of these enzymes and prevents them from digesting about a quarter of the fat you eat. Because undigested fat can’t be absorbed, it passes out of your body naturally.



The main side effect occurs when you eat a meal with too much fat while taking alli. If so much fat is blocked that your stool can’t absorb it, you might have side effects. Because they are not harmful, we call them “treatment effects”. They include loose or more frequent stools, an urgent need to go to the bathroom, or gas with an oily discharge. The excess fat that passes out of your body is in no way harmful. In fact, you may recognize it as something that looks like the oil on top of a pizza. Treatment effects can be lessened if you stick to reduced-calorie, low-fat meals that average 15 grams of fat per meal.

• Don’t use alli if you are pregnant or breastfeeding, if you have had an organ transplant, or if you are taking warfarin.
• Do not take alli if you are taking cyclosporine, or if you are allergic to any of the ingredients in alli capsules.
• Do not take alli if you are not overweight.
• You can take up to three alli capsules per day, one with each meal containing fat.