I think they all in the same "category" of weight loss drugs which is appetite surpressant. I have heard (and read) that Didrex is supposed to be the strongest. I don't know if that is true. I do know that Phentermine works wonders. Yes it give you energy. But as with all of them after a while they lose their effectivness. So you need to break with them every now and then for a couple of weeks.