PROBLEM TO BE SOLVED : To provide a novel non-hygroscopic form of nalmefene hydrochloride for oral dosage forms. SOLUTION : The invention provides a solid dosage form including a crystal of nalmefene hydrochloride dihydrate represented by the formula. Particles of the crystal have following particle size distribution : D90 equal to or less than 400 μm, D50 equal to or less than 200 μm, and D10 equal to or less than 50 μm, with the ratio D90/D50 equal to or less than 2.5, where the D10, D50 and D90 are defined as values such that particles having diameters smaller than the indicated values account for 10%, 50% and 90% by volume, respectively. SELECTED DRAWING : None COPYRIGHT : (C)2019, JPO&INPIT