A method for treatment of a systemic wasting disease, by administering, to a subject in need thereof, an effective amount of a 3,8-diaminotetrahydroquinoline derivative represented by formula (Ia) (wherein X represents CH2, C═O, CH—OR, CH—SR, or CH—NRR′; m is a number of 1 or 2; Ar represents a phenyl group, a naphthyl group, a 5-membered or 6-membered aromatic heterocyclic group having one or two elements selected from S, N, and O, or a similar group; R1 and R2, which may be identical to or different from each other, each represent a hydrogen atom or a methyl group; R3 represents a C1 to C6 alkyl group or a similar group; n is a number of 0 or 1; R4 and R5, which may be identical to or different from each other, each represent a hydrogen atom, or a C1 to C6 alkyl group, etc.; and R6, R7, R, and R′, which may be identical to or different from one another, each represent a hydrogen atom or a C1 to C6 alkyl group), or a salt thereof.