The weight ratio of the immediate-release drug to the prolonged-release drug is about 0.01:1 or less, preferably from about 0.001:1 to about 0.01:1. [0013] In certain preferred embodiments of the invention, the supporting matrix in controlled-release portion of the tablet is a material that swells upon contact with gastric fluid to a size that is large enough to promote retention in the stomach wh