A
morphinan derivative represented by the following general formula (I): (wherein R1 represents
hydrogen, C1-10
alkyl, cycloalkylalkyl where the cycloalkyl
moiety has 3 to 6 carbon atoms, and the alkylene
moiety has 1 to 5 carbon atoms, etc., R2 represents heterocyclic ring containing 1 to 4 heteroatoms selected from N, O and S and at least one
carbon atom as ring-constituting atoms, containing at least one set of adjacent ring-constituting atoms bound by a
double bond, and further substituted with at least one oxo group, Y binds to a
carbon atom as a ring-constituting atom of R2, R3, R4, and R5 represent
hydrogen; hydroxy, etc., R6a and R6b represent
hydrogen, etc., R7 and R8 represent hydrogen, etc., R9 and R10, which are the same or different, represent hydrogen, etc., X represents O or CH2, and Y represents C(=O)), a
tautomer or stereoisomer of the compound, or a pharmaceutically acceptable salt thereof, or a solvate thereof is used as an
anxiolytic drug,
antidepressant, etc.