What breast enhancement pills actually works?

None to my knowledge: I am not aware of any oral medications that will increase the breast size.

From nil to many: The effects will vary from virtually no side effects or results to more extensive effects particularly if they are hormonal analogues, with similar effects to oral contraceptives or estrogen replacement with head aches, weight or fluid gain, tenderness, masses, increased clotting tendencies, etc.

None: There is no safe way to grow or reduce breasts... Whether with supplements or medications. Augmentation with a plastic surgeon is the only safe way.