A drug that is useful for treating schizophrenia. In particular, a therapeut ic agent for schizophrenia comprising as an active ingredient a 4-acylamino- 5,6,7,8-tetrahydrofuro[2,3-b]quinoline derivative, or its optical enantiomor ph or acid adduct salt, or a hydrate or solvate thereof.
THERAPEUTIC AGENT FOR SCHIZOPHRENIA