The purpose of the present invention is to provide a solid preparation which contains a 4,5-epoxymorphinan derivative or a pharmacologically acceptable acid addition salt thereof, and which is stable against light without requiring a light-shielding coating. Provided by the present invention is a solid preparation that contains an active ingredient comprising a 4,5-epoxymorphinan derivative represented by formula (II) or a pharmacologically acceptable acid addition salt thereof, and at least one type of stabilizing agent selected from the group consisting of n-propyl gallate, sodium bisulfite, dibutylhydroxytoluene, butylated hydroxyanisole, tocopherol, and D-isoascorbic acid, wherein: the weight of the active ingredient accounts for 0.00001-0.01 wt% of the weight of the solid preparation； and the weight of the stabilizing agent accounts for 0.005-5 wt% of the weight of the solid preparation.本發明係以提供即使未進行遮光性包衣(coating)亦對光為穩定之含有4,5-環氧基嗎啡喃衍生物或其藥理學上可容許的酸加成鹽之固體製劑為目的。本發明係提供一種固體製劑，其含有包含以下所代表之4,5-環氧基嗎啡喃衍生物或其藥理學上可容許的酸加成鹽之有效成分；及選自包含沒食子酸正丙酯、亞硫酸氫鈉、二丁基羥基甲苯、丁基羥基苯甲醚、生育酚及D-異抗壞血酸的群組之1種以上之穩定化劑，其中上述有效成分之重量係每固體製劑重量的0.00001~0.01重量%，上述穩定化劑之重量係每固體製劑重量的0.005~5重量%。
