A powdered, dispersible composition having stable dispersibility over time is provided. The composition exhibits a characteristic glass transition temperature (T.sub.g) and a recommended storage temperature (T.sub.s), wherein the difference between T.sub.g and T.sub.s is at least about 10.degree. C. (i.e. T.sub.g -T.sub.s is greater than 10.degree. C.). The composition comprises a mixture of a pharmaceutically-acceptable glassy matrix and at least one pharmacologically active material within the glassy matrix. It may be further mixed with a powdered, pharmaceutically-acceptable carrier. It is particularly valuable in unit dosage form having a moisture barrier, in combination with appropriate labelling instructions. A process for producing a powdered dispersible composition is also provided, wherein the process comprises removing the solvent from a solution comprising a solvent, a glass former and a pharmacologically active material under conditions sufficient to form a glassy matrix having the pharmacologically active material within the matrix.