it blocks the break down and absorbtion of fats, so cuts down your calorie intake.
However, you have to use it with a low fat diet. the undigested and unabsorbed fat will end up in your poo, and you can get 'ahem' leakage and flatulance if you don't limit the fats. In other words if you pork out , you'll have the shits.
It isn't an amphetamine.
It can seriously help weight loss, but on if used in conjunction with a low fat , healthy diet. But it does help people along, IYSWIM