Are diet herbal medicines really effective?

I think proper diet control is the most important for effective dieting. I always have a lot of fat around my belly, sides, and other areas.
I'm worried, but I've never tried diet pills or diet herbal medicine, although I know many people around me who are taking diet herbal medicine.
I am curious about whether I am managing my diet well, if I am experiencing any yo-yo effects, and how much I need to eat to see results.