SoulBliss is absolutely right.
If you look in the fine print for any of those diet pills, they all say you have to diet and exercise along with the pill in order to get results. In other words, it's the diet and exercise, not the pill, that works. So why not skip the pill and save the money?
Seriously, I'm the moderator of the Maintainers forum here at 3FC for members who have reached their goals and are maintaining. We have many successful losers here and I can tell you that not a one of them did it with diet pills. Because diet pills don't work. Lifestyle changes incorporating healthy eating and exercise are what will get you to your goal and keep you there.