Abstract: AIM: To study the efficacy and side effects of both middle and low doses of risperidone in the treatment of first-episode schizophrenia, and to investigate the relationshiPbetween plasma concentration of RSP, 9-OH-RSPand the efficacy or side effects occurred during RSPtreatment.METHODS: Compared the patients treated with middle dosage of risperidone ( groupB, 40 cases) and the other 42 cases ( groupA) that are treated with very low dosage of risperidone.RESULTS: Two groups were in statistical difference ( P<0.05) by itself.But there were no significant difference between grouPA and grouPB ( P<0.05).GrouPA took effect later than grouPB.Total scores of the treatment emergent symptom scale ( TESS) were significantly lower in grouPA than in grouPB.The plasma concentration of 9-OH-RSPand the active moiety ( RSP+9-OH-RSP) after one week' s administration of risperidone were higher in grouPB than that in grouPA ( P<0.05).CONCLUSION: This assay suggested that low dosage of risperidone is effective,safe and beneficial in the treatment of first-episode schizophrenia.

Key words: risperidone, 9-hydroxyrisperidone, First-episode schizophrenia, efficacy, side effects