Alli can help people lose a modest amount of weight. People who take Alli are sometimes able to lose a few more pounds than they were able to lose through lifestyle modifications alone. In most cases, the use of Alli alone does not result in significant weight loss.
Alli works by reducing the amount of fat the body can absorb. Taking Alli results in fewer calories absorbed by the body. When Alli is taken with a high-fat meal, side effects such as diarrhea or gas that results in underwear spotting may occur. Alli is available over the counter and is intended only for individuals who are overweight.