A monolithic sustained-release pharmaceutical composition comprising a therapeutically effective dose of metformin hydrochloride as an active substance and a hydrophobic polymer and/or other hydrophobic material, wherein the metformin hydrochloride is released no more than forty percent in gastric fluid having pH 1.2 and is released no less than ninety percent eight to ten hours after administration in simulated intestinal fluid (phosphate buffer) having pH 6.8, and wherein the metformin hydrochloride displays a peak plasma concentration, a systemic bioavailability over time, and a residual plasma concentration twenty-four hours after administration of an oral dosage form of the pharmaceutical composition, so that the metformin hydrochloride concentration remains therapeutically effective and once daily administration of the pharmaceutical composition is sufficient to be therapeutically effective throughout a day.
