This invention provides a storage-stable dosage form of a thyroxine active drug composition which exhibits an improved stability. The formulation contains a thyroxine active drug substance, an alditol, and a saccharide, and, optionally, additional pharmaceutically accepted excipients. Levothyroxine sodium is the preferred active drug substance, mannitol is the preferred alditol, and sucrose is the9 preferred saccharide. Additional preferred excipients include, for example, microcrystalline cellulose, crospovidone, magnesium stearate, colloidal silicon dioxide, and sodium lauryl sulfate.