Therapeutic duplication (TD) is frequently reported inappropriate drug use in healthcare settings in Korea. This study was aimed to develop TD criteria for psycho-nervous system drugs (KFDA classification 117 and 119). ATC classification was used to determine therapeutic and/or chemical similarities among the 93 ingredients reviewed. Clinical practice guidelines, textbooks and product labels were referenced for principles and evidences of possible drug combination usage. 16 groups that listed ingredients to be considered as TD were established and the criteria would be helpful to prevent TDs.