Please don't use diet pills! They sound great but really, the best way is still a healthy eating plan and a little more exercise.
The advertising for these things is completely false and misleading. But there is a much more important reason not to use them.
They could lead to health issues later down the road. Some ingredients have caused heart conditions like Pulmonary Hypertension. Some of these we know about, but how many other ingredients out there are causing problems we DONT know about yet? Don't gamble on your health.
I have Pulmonary Hypertension, and while mine was not caused by diet pills, since I never used them, I have gotten the point. Every consultation I go to, the first question is always the same. Did I ever use diet pills. Its not worth the risk. Trust me, PPH is NOT FUN. And there is no cure.
Edited to add:
Notice how many people SELLING these things were quick to chime in? It is a moneymaking venture that preys on women's societal conditioning to be their most attractive and ornamental for the menz who have to look at us. (Not your fiance, just men and society in general)
These things also completely mess up your metabolism. They raise it while you're using it, then when you stop your body doesn't know what its supposed to do and can just go completely out of whack because it forgets what it was doing before you messed with it. It messes with other body processes and can be hard to recover from.
Use common sense instead of tricks and shortcuts. You only have one body, take care of it.