As with a lot of diet pills(not all) I think all this pill could offer is a bit of a "placebo effect", making the people taking them subconciously(or even conciously) make better food choices and maybe eat less causing them to lose some weight, and then they belive it was because of the diet pill.
When you think of it you don't often see ladies start taking diet pills WITHOUT also being like "I'll try eat healthier and walk more", so I belive that's where the results in most cases actually come from.