The invention relates to a solid oral extended release pharmaceutical dosage form comprising an extended release matrix formulation. The extended release matrix fomiulation comprises (1) at least one active agent, (2) at least one anionic surfactant, and (3) at least about 40% by weight (based on the weight of the extended release matrix formulation) of at least one polyethylene oxide. In certain embodiments, the molar ratio of the at least one anionic surfactant to the at least one active agent is from about 1 :2 to about 10: 1.
