I have never found any of the over the counter "bleaching" products to be particularly effective. Some of the whitening toothpastes are simply more coarse than the usual toothpastes and remove external staining (eg coffee, tea and red wine staining), but most people seem to be after an actual change in their tooth colour.

This can only really be achieved using strong bleaching agents, and should be done under the supervision of a trained professional.