Compound for use in the treatment of diarrheal irritable bowel syndrome comprising, as an effective ingredient, a morphinan derivative having a nitrogen-containing cyclic substituent of the formula (I): ** Formula ** [in which R1 is hydrogen, C1-C5 alkyl, C4-C7 cycloalkylalkyl, C5-C8 cycloalkenyl alkyl, C6-C12 aryl, C7-C13 aralkyl, C3-C7 alkenyl, furanylalkyl alkyl (in which the number of carbon atoms in the alkyl moiety is 1 a 5), thienyl alkyl (in which the number of carbon atoms in the alkyl moiety is 1 to 5) or pyridyl alkyl (in which the number of carbon atoms in the alkyl moiety is 1 to 5)； R2 and R3 are independently hydrogen, hydroxy, C1-C5 alkoxy, C3-C7 alkenyloxy, C7-C13 aralkyloxy or C1-C5 alkanoyloxy； Y and Z independently represent valence bond or -C (>； = O) -； -X- represents C2-C7 alkylene, alkenylene or alkynylene (one or more of the carbon atoms therein may be substituted by an atom of nitrogen, oxygen and / or sulfur atoms) that constitutes a part of the ring structure； k is an integer from 0 to 8； R4 is or is a substituent or substituents in number of k in the ring containing nitrogen, which independently represents or represents fluorine, chlorine, bromine, iodine, nitro, C1-C5 alkyl, C1-C5 alkylidene, C7-C13 cycloalkylalkyl, aryl C6-C12, aralkyl C7-C13, aralkylidene C7-C13, trifluoromethyl, trifluoromethoxy, cyano, isothiocyanate, (CH2) pSR6, (CH2) pS (O) R6, (CH2) pS (O2) R6, (CH2) pR6, (CH2) pC (>； = O) R6, (CH2) pOC (>； = O) R6, (CH2) pCO2R6, (CH2) pS (O2) NR7R8, (CH2) pC (>； = O) NR7R8, (CH2) pNR7R8, (CH2) pN (R7) C (>； = O) R8, (CH2) pN (R7) S (O2) R8, or between R4 in number of k, two R4 linked to the same or at the same carbon atom Sulfur atom together represent an oxygen atom to form carbonyl or sulfoxide, or two R4 bonded to the same carbon atom together represent a sulfur atom to form thiocarbonyl, or four R4 bonded to the same sulfur atom together represent two oxygen atoms to form sulfone, or between R4 in number of k, two
