alli works by inhibiting some of the body’s absorption of dietary fat. Taken at meal times, it works by blocking the absorption of about 25% of fat in the foods you eat. Because of the way it works, alli must be used in conjunction with a reduced-calorie, low-fat diet containing about 15 grams of fat per meal. Eating a meal with too much fat while taking alli can result in bowel changes, such as loose stools, more frequent stools that may be hard to control, or gas with oily spotting. These changes, called treatment effects, may occur in the first weeks of treatment, are not harmful and can generally be managed by following a reduced-calorie, low-fat diet that does not exceed 15 grams of fat per meal.
alli works in the gut; it is nonsystemically acting, which means it does not affect the central nervous system (CNS) and has no effect on the heart or the brain. Some weight-loss drugs and supplements that are systemically absorbed can be associated with CNS side effects (e.g., seizure, stroke and anxiety) or systemic side effects (e.g., heart palpitations, elevated blood pressure and heart problems). alli, a nonsystemic weight-loss aid, is not associated with these side effects, and its safety and efficacy are well established.
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