The present invention provides a novel method for treatment of schizophrenia which can improve wide-ranging symptoms of schizophrenia, especially positive symptoms and negative symptoms without being accompanied by extrapyramidal symptoms, which comprises orally administering as an active compound (1R,2S,3R,4S)-N-Ä(1R,2R)-2-Ä4-(1,2-benzoisothiazol-3-yl)-1-piperazinylmethylÜ-1-cyclohexylmethylÜ-2,3-bicycloÄ2.2.1Üheptanedicarboxy imide or a pharmaceutically acceptable salt thereof (e.g., hydrochloride) at a daily dose of 5 mg to 120 mg once a day to a patient with schizophrenia, and a therapeutic agent to be used in said method.
