How Does Alli Work?
Alli works in the gut to reduce the amount of fat
your body absorbs from a meal. It inhibits the action of the enzyme
lipase which is necessary for the absorption of fats in the small
intestine and stomach.
Undigested fats are not absorbed and therefore do not add to the caloric
balance of any particular meal. This may result in a reduced caloric
intake, and therefore, weight loss.

Of course, Alli only blocks the absorption of fat. If you're consuming
low fat meals, you don't need Alli, Xenical or Orlistat. It won't do
anything to inhibit the absorption of "carbohydrate" calories.
It's important to make note of this as there's been a continuing trend
of a reduced fat intake over the last few decades, while carbohydrate
intake has continued to increase.
In other words, if most of your "bad" calories come from sweets, and not
fats, Alli is not for you.
The good news is that like Xenical, very little if any Alli actually
enters the bloodstream. It works in the gut and the small intestine.
That means it won't effect the central nervous system like most diet
pills.
The bad news is that neither Alli or Xenical differentiate between
blocking the "bad" saturated fats and good, cholesterol-lowering poly
and monounsaturated fats.
Both drugs also inhibit the absorption of fat soluble vitamins and
beta-carotene making supplementation with a quality multi-vitamin
necessary when using either Alli or Xenical.

Buy Alli
What are the Alli side effects?
Read the Alli Discussion here
Ugh.
Prepare yourself for some unpleasantness. Because the fat in a meal
does not get absorbed, it has to leave your body somehow -- and that's
through the stool.
When taken with a high fat meal, possible side effects include
bloating, gas, "oily spotting," diarrhea, and possibly, "anal leakage."
The best way to reduce these nasty side effects is to limit the
amount of fat consumed in any meal -- no more than 30% of any meal's
calories should come from fat.
It's although worth noting that The Public Citizen's Health Research
Group (a non profit advocacy group) does not like Xenical, Alli, or
Orlistat at all, claiming they can cause gallstones and pre-cancerous
abnormalities.
What about Alli's interactions with other drugs? Alli interacts with
both warfarin (it increases its effect) and the antibiotic cyclosporine
(it decreases its effect).
Bottom line?
Although available over the counter, Alli is, for all intents and
purposes, a drug. It should be treated with respect and I would not
recommend you take it without first consulting with your physician --
especially if you are taking any other medication.
Is Alli Right For
You?