The starting dose of risperidone is 2 mg/day. After administration for 3 consecutive days (Days 1~3 of medication), the dose will be increased to 4 mg/day administered for additional 3 consecutive days (Days 4~6 of medication). From Day 7, the dose can be either increased to 6 mg/day or maintained at 4mg/day until the end of the double-blind treatment period.