The morphinan derivatives represtented by the following general formula (I), tautomers, isostereoners or pharmaceutical acceptable salt thereof or solvate thereof are used as anxiolytics, antidepressants and the like. (wherein, R1 represents hydrogen, C1-10 alkyl, cycloalkylalkyl having a carbon numbers of 3 to 6 at cycloalkyl part and having a carbon numbers of 1 to 5 at alkylene part, and the like, R2 represents a hetero ring containing 1 to 4 hetero atoms selected from N, O and S and at least one carbon atom as the ring constituting atoms, having a double bond in at least one set of the adjacent ring constituting atoms, and further being substituted by at least one oxo group, Y binds with a carbon atom which is a ring constituting atoms of R2, R3, R4 and R5 represent hydrogen, hydroxyl and the like, R6a and R6b represent hydrogen and the like, R7 and R8 represent hydrogen and the like, R9 and R10 are the same or different, represent hydrogen and the like, X represents O or CH2, and Y represents C(=O)).使用以下通式(I)所表示之嗎啡喃衍生物、該化合物之互變異構物、立體異構物、或其藥學上可容許之鹽或彼等之溶劑合物作為抗焦慮藥、抗憂鬱藥等。(式中，R1表示氫、C1-10烷基、環烷基部分之碳原子數為3至6且伸烷基部分之碳原子數為1至5之環烷基烷基等；R2表示以選自N、O及S之1至4個雜原子及至少1個碳原子作為環構成原子，而且鄰接之環構成原子的至少1組具有雙鍵，並進一步經至少1個側氧基取代的雜環；其中，Y與為R2之環構成原子的碳原子鍵結；R3、R4及R5表示氫、羥基等；R6a及R6b表示氫等；R7及R8表示氫等；R9及R10為相同或相異，表示氫等；X表示O或CH2；再者，Y表示C(=O))。
