WE CLAIM:
1. A solid preparation comprising an active ingredient composed of a
4,5-epoxymorphinan derivative represented by the general formula (I) below or a
pharmaceutically acceptable acid addition salt thereof, and one or more stabilizing
agents selected from the group consisting of /i-propyl gallate, sodium hydrogensulfite,
dibutylhydroxytoluene, butylhydroxyanisole, tocopherol and D-isoascorbic acid,
wherein the amount of the active ingredient is 0.00001 to 0.01% by weight of the solid preparation, and
wherein the amount of the stabilizing agent is 0.005 to 5% by weight of the solid preparation
[wherein R represents cyclopropylmethyl or allyl; R represents hydrogen, hydroxy, acetoxy, or methoxy; R represents hydrogen, hydroxy, acetoxy, or methoxy; A represents -N(R4 )C(=0)- or -N(R4 )C(=0)0-; R4 represents hydrogen or a C1.5 linear or branched alkyl; B represents a C1.3 linear alkylene, -CH=CH-, or -C=C-; R5 represents hydrogen, phenyl, furyl, or thienyl, provided that a hydrogen(s) in the phenyl, the furyl and the thienyl is/are optionally substituted with one or more groups selected from the group consisting of C1.5 alkyl, C1.5 alkoxy, C1.5 alkanoyloxy, hydroxy, fluorine, chlorine, bromine, iodine, amino, nitro, cyano, isothiocyanato, trifluoromethyl, trifluoromefhoxy and methylenedioxy].
2. The solid preparation according to claim 1, wherein the stabilizing agent is ^-propyl gallate.
3. The solid preparation according to claim 1 or 2, which contains sodium

thiosulfate.
4. The solid preparation according to any one of claims 1 to 3, which contains yellow ferric oxide, red feme oxide, or black iron oxide.
5. The solid preparation according to any one of claims 1 to 4, which contains a carbohydrate.
6. The solid preparation according to any one of claims 1 to 5, which is in a dosage form selected from the group consisting of tablet, granule, fine granule, hard capsule, dry syrup, powder, pill and troche.